Covalent Bond - chemya.weebly.comchemya.weebly.com/.../28974683/covalent_bonds_2018.pdf · Single Bond When Single covalent bonds Sometimes atoms need a single electron to reach an

Grade 10

Term nd2

20182017

تستخدم أوراق العمل للمساعدة على أداء األنشطة داخل الصف،

وال تغين عن الكتاب املدرسي

Covalent Bond

10th Grade

2nd Term, 2018

( 1 ) http://chemya.weebly.com/

Chemistry

Stability

All atoms are electrically neutral, because the number of positive protons forming the

nucleus is equal to the number of negative electrons rotating around the nucleus. In

repulsion, not all atoms are stable. Many atoms have high energy that makes them

unstable, forcing them to try to reach stability by reducing their energy. Chemical bonds

where the atom loses or acquires or shares valence electrons with other atoms.

Covalent bond: is the force of attraction that holds together two atoms that share a pair of

valence electrons.

Molecule: is the smallest particle of a covalent compound that still has the properties of the compound.

➢ As with ionic bonds, the electrons involved in covalent bond formation are those

occupy the last level of atoms (valence electrons)

➢ Covalent bonds often consist of non-metals.

➢ The covalent bond binds the atoms in diatomic molecules (H2, F2, O2, Cl2)

Why Covalent Bonds Form?

Covalent bonds form because they give atoms a more

stable arrangement of electrons. Look at the Oxygen

atoms in the Figure above. Alone, each Oxygen atom has

six valence electrons. By sharing two pairs of valence

electrons, each Oxygen atom has a total of eight valence

electrons. This fills its outer energy level, giving it the most

stable arrangement of electrons. The shared electrons are attracted to both Oxygen nuclei,

and this force of attraction holds the two atoms together in the Oxygen molecule.

Forces in molecules Fluorine atom (9F) has an electron configuration (1s22s22p5). Each Fluorine atom has seven

valence electrons and needs only one electron to reach the Octet. As the Fluorine

approaches each other, the electrical forces affect the state of the atoms.

The closer the two atoms are, the greater the attraction between the nucleus and the

electrons of the other atom until it reaches a point where the attraction forces between the

nuclei and electrons are greater than the repulsion forces between the nuclei, as well as

between the electrons in both atoms. Here the covalent bond is composed in the Fluorine

molecule (F2).

Attraction

The shared electrons are attracted to the nuclei of both atomsBetween The electrons

of both atoms

Between The nuclei

of both atoms

Repulsion

Forces

https://www.ck12.org/c/chemistry/compound

10th Grade

2nd Term, 2018


Chemistry

By sharing one pair of electrons the two atoms reach an electron configuration similar to the

electron configuration of the nearest noble gas.

For each Fluorine atom, one pair of shared electrons (bonded electrons) and three not shred

pairs (unbonded electrons).

Numbers of bonds

Single covalent bonds

Sometimes atoms need a single electron to reach an electron configuration similar to noble

gas, with the participation of one pair of electrons. These atoms reach the stability state, as

in Fluorine in the previous example, or as Hydrogen Molecule H: H or H-H

The atom does not necessarily have to be associated with another atom of the same kind to

stabilizes, two different atoms can make a covalent bond by the participation of the electrons.

Single Bond

When only one paire of electrons is shared

When three paires of electrons is shared

When two paires of electrons is shared

Multible Covalent Bonds

Trible Bonds Double Bonds

Covalent Bonds

10th Grade

2nd Term, 2018


Chemistry

Group 17 elements contain seven (7) valence electrons, they lack a single electron until

they reach stability. For example, the bond between Hydrogen and Fluorine is as follows,

H· + H ـــ

Group 16 elements, contain six (6) valence electrons, they need two electrons until the last

level complete with 8 electrons. Oxygen, for example, with electron configuration (1s22s22p4)

have two single covalent bonds with Hydrogen, one Oxygen atom shares a pair of electrons

with each Hydrogen atom to form a water molecule.

Group 15 elements, contain five (5) valence electrons, they need three electrons to reach

the last level complete with 8 electrons. Nitrogen , for example, its electron configuration

(1s22s22p3) have three single covalent bonds with Hydrogen, they share three pairs of

electrons, a pair with each Hydrogen atom to form the ammonia molecule.

Nitrogen can also combine with an element of group 17 such as Chlorine to form a Nitrogen

trichloride compound.

+

Group 14 elements, contain four (4) valence electrons, each one need four electrons until

it reaches the last level complete with 8 electrons. Carbon, for example, its electron

configuration (1s22s22p2) have four single bonds with atoms that share one pair of electrons,

it shares four pairs of electrons, a pair with each atom. For example, in a Chlorofluorocarbon

(CFC) used in refrigeration, the carbon atom is connected to four Chlorine and Fluorine

atoms,

· · · F :

· ·

· · F :

· ·

·

· N :

·

· ·

· Cl :

· ·

─ N :

· ·

: Cl :

│

· ·

: Cl

· ·

│

: Cl :

· ·

3

· · C ·

·

· · · Cl :

· ·

─ C

· · : Cl : │

· · : F

· · │

: Cl : · ·

· · · F :

· ·

· · ─ Cl :

· · 3 + +

10th Grade

2nd Term, 2018


Chemistry

1) How does the covalent bond form?

_____________________________________________________________________________________________________________________

2) What is the smallest unit of the Covalent Compound formed by the chemical bonding of two or more atoms?

_____________________________________________________________________________________________________________________

3) Which types of elements used to form covalent bonds?

_____________________________________________________________________________________________________________________

4) What is the result of the participation of two atoms of the same element in valence electrons?

_____________________________________________________________________________________________________________________

5) Why do molecules consist of atoms rather than being atoms alone?

_____________________________________________________________________________________________________________________

6) What types of forces influence the components of atoms in molecules?

_____________________________________________________________________________________________________________________

7) Complete the following table,

Influential Forces

Suitable situation to form the bond

8) Draw the shape of the fluorine molecule

a) How many pairs of electrons are involved in each atom? ______________________________

b) How many pairs of unconnected atoms per atom? _______________________________________

9) What is the bond formed by the participation of one pair of electrons?

_____________________________________________________________________________________________________________________

10) Sketch Hydrogen molecule using Lewis structure.

10th Grade

2nd Term, 2018


Chemistry

11) Complete the following tables.

Group 14 Group 15 Group 16 Group 17

# Valence electrons

# Electrons required for stability

# Electrons participate in the formation of the bond

# Created bonds

12) Draw the Lewis structure for

Cl2 HCl

13)

water H2O H2S

14)

NH3 phosphine PH3

15)

CH4 SiH4 CCl4

10th Grade

2nd Term, 2018


Chemistry

Hybridization The electron configuration in the carbon atom is (1s22s22p2). As it is clear, the carbon atom

ends with a (p) sub-level containing only two electrons, it is easy to conclude that only these

two electrons are involved in the bond formation. But we have studied that carbon has four

bonds, and the reason is hybridization.

Electronic configuration of carbon atom

Hybridization between level 2s and 3p levels

produces four hybrid levels sp3

Hybridization: mixing sub-levels to form new hybrid levels

The number of hybrid levels produced is equal to the total number of levels entered in the

hybridization process. In the previous example, one orbital of 2s with three orbitals of 2p was

hybridized to produce four sp3 hybrid levels.

The sublevel (s) consists of a single orbital and sublevel (p) of three orbitals, making three

possibilities of hybridization, and the number of orbitals resulting from the hybridization is

equal to the total number of hybridized orbitals.

Orbitals overlapping The shapes of the orbitals in the sub-levels are varied. The sub-level (s) has a spherical

shape, while the three orbitals of the sub-level (p) are pear shaped in each of the three

directions.

s orbital p orbital

Hyberdization between s,p

Sp3 sp

* Form when the sub-

level (s) is mixed with

one sub-level (p) orbital.

* Produces two hybrid

orbitals with two non-

hybridized (p) orbitals.

* Form when the sub-

level (s) is mixed with

three sub-level (p)

orbitals.

* Produces four

hybrid orbitals.

* Form when sub-level

(s) is mixed with two

sub-level (p) orbitals.

* Produces three hybrid

orbitals with a non-

hybridized (p) orbitals.

Sp2

10th Grade

2nd Term, 2018


Chemistry

Bonds are formed when orbitals overlap and there are two possibilities for such overlapping,

Multiple covalent bonds We have learned before that it is enough to some atoms to share one pair of electrons to

reach stability, such as bromine, while some atoms need to share more than one pair to be

stable like the elements in groups 14, 15 and 16 so the atoms of these elements make more

than one bond.

Double bonds

The Oxygen atom at the top of group 16 has 6 valence electrons, needs two electrons for a

noble-gas configuration. This is what happens when interacting with two Hydrogen atoms to

form a water molecule. But there is another way, by sharing two pairs of electrons with

another Oxygen atom. The two atoms are bound together by two bonds, one of them is

sigma (σ) and the other is pi (π).

Triple bonds

The elements in group 15, such as Nitrogen , have 5 valence electrons and need three

electrons for a noble-gas configuration, so they bonded by three pairs of electrons. The

Nitrogen atom can make three single bonds with other elements such as Hydrogen or a triple

bond with a similar Nitrogen atom.

Hed to hed (end to end) Side by side (parallel)

* The electronic density is low and

the bond is weak.

* The pi bond (π) is formed.

(s) with ( s)

(p) with ( p)

(s) with (p)

When hybrid levels

are involved in

association formation

* The electronic density is high and the

bond is strong.

* The sigma bond (σ) is formed

Orbitals overlaping

One σ bond, one π bond

One σ bond, two π bond

10th Grade

2nd Term, 2018


Chemistry

Covalent bond strength

Remember that there are forces of attraction and repulsion between the electrons and nuclei

of the atoms that participate together to form a covalent bond. The molecule stabilizes when

the forces of attraction overcome the forces of repulsion. To break these forces we need

energy, the forces of attraction and repulsion vary in the compound, so the energy values

that are needed to break the covalent bond vary.

Bond length

Covalent bond length: the distance between the two the two bonded nuclei at the position of

maximum attraction.

The strength of the bond depends on the length of the bond. The length of the bond depends

on the strength of the attraction between the charges involved in the composition of the bond

and depends on the number of charges, the greater the number of charges the stronger the

attraction between them and thus the length of the bond decreases and its energy increase.

Molecule Bond type Bond length Bond-Dissociation Energy

F2 Single bond 1.43 × 10-10 m 159 kJ /mol

O2 Double bond 1.21 × 10-10 m 498 kJ /mol

N2 Trible bond 1.10 × 10-10 m 945 kJ /mol

It is clear from the table that trible bonds are shorter and have higher energy than double

bonds as well as double bonds are shorter than single bonds and higher energy.

Energy and bonds

It emits energy when forming bonds and in contrast we need energy to break those bonds.

Bond-Dissociation Energy: energy needed to break the covalent bond.

From the above table, it is clear that the bond dissociation energy depends on its type as

well as the length of the bond, the shorter the bond the greater energy needed to break.

The chemical reaction is simply defined as the breaking down bonds and forming new bonds.

As we have already said, breaking bonds requires energy. While the formation of bonds

produces energy, the reaction finally has energy equals to the difference between the energy

value we need to break the bonds and the energy that results from the bonds formation.

Endothermic Reaction Exothermic Reaction

When the energy emitted by the bonds

in the outputs is lower than the energy

needed to break the bond in the

reactants.

When the energy emitted by the bonds

in the outputs is greater than the

energy needed to break the bond in

the reactants.

The difference between the energy generated by the bonds formation and the energy needed to break the bonds

10th Grade

2nd Term, 2018


Chemistry

16) Compare between the Sigma bond and the pi bond

Sigma bond σ pi bond π

How does it consist?

Bond energy

Number between two atoms

presence of electrons

17) What is the result when atoms share with more than one pair of electrons? _____________________________________________________________________________________________________________________

18) What is the result when atoms share with two pairs of electrons?

_____________________________________________________________________________________________________________________

19) Draw the Lewis structure of oxygen molecule O2

20) How many Sigma and Bi bonds are in the Oxygen molecule?

_____________________________________________________________________________________________________________________

21) What is the result when atoms share with three pairs of electrons?

_____________________________________________________________________________________________________________________

22) Draw the Lewis installation of the Nitrogen molecule N2

23) How many Sigma and Bi bonds are in the Nitrogen molecule? _____________________________________________________________________________________________________________________

24) How can I break the covalent bond? _____________________________________________________________________________________________________________________

25) Defined Covalent Bond Length. _____________________________________________________________________________________________________________________

26) Draw the Lewis structure for ethyne C2H2.

10th Grade

2nd Term, 2018


Chemistry

27) What is the relationship between the length of the bond and the number of electrons involved?

_____________________________________________________________________________________________________________________

28) What is the relationship between the length of the bond and the strength of the bond?

_____________________________________________________________________________________________________________________

29) Draw a graphical curve between the length of the bond versus the energy of the bond and clarify the relationship between them.

_____________________________________________________________________________________________________________________

30) Defined Bond-Dissociation Energy. _____________________________________________________________________________________________________________________

31) What is the relationship between the length of the bond and the its dissociation energy? _____________________________________________________________________________________________________________________

32) What is the relationship between (bond formation / breaking) and (energy)? _____________________________________________________________________________________________________________________

What type of reaction when, 33) The energy generated by the bonds formation in products is greater than the energy needed to break the bonds in the reactors? _____________________________________________________________________________________________________________________

34) The energy produced by the bonds formation in products is less than the energy needed to break the bonds in the reactors? _____________________________________________________________________________________________________________________

35) Which of the following compounds has the shortest bond between its components? * H2 *O2 * Cl2 * N2

36) Select Sigma and Bay bonds in the following vehicles.

37) Define double Bond _____________________________________________________________________________________________________________________

10th Grade

2nd Term, 2018


Chemistry

1) 38)which one of the Nitrogen -carbon bonds are shorter and weaker in the following compounds?

The table represents the bond energy values of some bonds between elements.

39) Predict the dissociation energy of covalent bonds for all that comes,

10th Grade

2nd Term, 2018


Chemistry

Naming molecules Naming of binary molecular compounds

To name simple covalent compounds, follow these rules:

• Start with the name of the element closer to the left side of the periodic table.

• Follow this with the name of element closer to the right of the periodic table. Give this

second name the suffix –ide.

• Use prefixes to represent the numbers of the different atoms in each molecule of the

compound.

The binary molecular compounds consist only of two non-metals, such as P2O5, which is

used as a dehydrating substance.

5O2P

Di Phosphorus penta oxide Prefix #atoms Prefix #atoms

hexa 6 mono 1

hepta 7 di 2

octa 8 tri 3

nona 9 tetra 4

deca 10 penta 5

NameCompoundNameCompound

Nitrogen dioxideN2ONitrogen trifluoride NF3

Carbon dioxide CO2 Carbon tetrachloride CCl4

Common names Some compounds have common names and this is because they have been used for a long

time and have been given names by people even before they are chemically categorized,

such as,

Chemical name Common name

Hydrogen dioxidewaterH2ONitrogen dioxideNitrous OxideN2ONitride tri Hydride AmmoniaNH3

Di Nitrogen tetrahydride HydrazineN2H4 Nitrogen monoxide Nitric OxideNO

Prefix (penta)

Number of atoms

Oxygen

2nd non-metal

Prefix (di)

Number of atoms

Phosphorus

1st non-metal

10th Grade

2nd Term, 2018


Chemistry

Naming acids Acid: The compound produces Hydrogen ions (H+) in solution, it is an acid.

When hydrochloric acid is placed in water it breaks down to H+ and Cl-

HCl H+ + Cl-

There are Two common types of acids exist binary acids and oxyacids.

naming binary acids Binary acids: An acid made up of Hydrogen and a non-metal.

Naming rules 1) We use the (Hydro) prefix at the beginning of the name.

2) followed by the name root of the non-metal followed by the suffix (ic)

3) We end with the conclusion (acid)

HCl

Hydrochloric acid

Naming Oxyacids Oxyacid: An acid that contains both a Hydrogen atom and an oxyanion.

Oxyanion ions: polyatomic ion containing one or more oxygen atoms.

Naming rules 1) We start with the name of the non-metal or its root.

2) We conclude with the suffix suitable for number of Oxygen atoms in Oxyanion that can be

deduced from the following table,

3) Second word is always (Acid)

OxyacidOxyanion

FormulaNameSectionSectionNameFormula

HClO hypochlorous acidhypo--ousHypo--itehypochlorite ClO-

HClO2Chlorous AcidousiteChloriteClO2-

HClO3Chloric acidicatechlorateClO3-

HClO4perchloric acidperr--ic perr--ate PerchlorateClO4-

** Some acids are multi-atoms but do not contain Oxygen, so we use the same rules that we

use with binary acids. Such as HCN, which is called hydrocyanic acid. Whose name is

derived from the cyanide ion (CN).

conclusion (acid)

suffix (ic)

Non-metal name root (Chlor)

Prefix (Hydro)

10th Grade

2nd Term, 2018


Chemistry

Names and formulas for some famous acids

Name Formula Name Formula

Hydrobromic acid HBr Sulfurous acid H2SO3

Acetic acid HC2H3O2 (or HCH3COO, or HCH3CO2)

Chlorous acid HClO2 Chloric acid HClO3

Hydrochloric acid HCl Nitric acid HNO3

Phosphoric acid H3PO4 Carbonic acid H2CO3

Hydrofluoric acid HF Perchloric acid HClO4

Hypochlorous acid HClO Permanganic acid HMnO4

Sulfuric acid H2SO4 Boric acid H3BO3

Hydrocyanic acid HCN Nitrous acid HNO2

Hydroiodic acid HI Phosphorous acid H3PO3

40) Write the names for the following covalent compounds:

1. SiCl4 ___________________________________ 2. CO2 _______________________________________

3. SCl4 ___________________________________ 4. SiBr6 _______________________________________

5. NCl3 ___________________________________ 6. SeBr2 _______________________________________

7. P2O3 ___________________________________ 8. N2O5 _______________________________________

9. SCl6 ___________________________________ 10. OF2 _______________________________________

11. NF3 ___________________________________ 12. Si3N4 _______________________________________

13. SF4 ___________________________________ 14. CS2 _______________________________________

15. P2S5 ___________________________________ 16. As2O3 _______________________________________

17. PBr5 ___________________________________ 18. B2O3 _______________________________________

19. SeF6 ___________________________________ 20. NF4 _______________________________________

21. CO2 ___________________________________ 22. NO _______________________________________

23. SO2 ___________________________________ 24. SeO3 _______________________________________

25. NF3 ___________________________________ 26. SO3 _______________________________________

27. CCl4 ___________________________________ 28. N2O4 _______________________________________

29. P2O5 ___________________________________

10th Grade

2nd Term, 2018


Chemistry

41) Write formulas for the following:

1. Tetraiodine nonoxide _______________ 2. tetraphosphorus decoxide _______________

3. DiNitrogen trioxide _______________ 4. Phosphorus triiodide _______________

5. Iodine heptafluoride _______________ 6. Diboron hexahydride _______________

7. Silicon tribromide _______________ 8. Iodine trichloride _______________

9. Phosphorus trihydride _______________ 10. Nitrogen tribromide _______________

11. Hexaboron silicide _______________ 12. DiNitrogen pentoxide _______________

13. Carbon monoxide _______________ 14. Sulfur hexachloride _______________

15. Carbon tetrachloride _______________ 16. Phosphorus trinitride _______________

17. Hydrogen monosulfide _______________ 18. Diphosphorus pentoxide _______________

19. Diboron tetrabromide _______________ 20. Disulfur decafluoride _______________

21. Sulfur trioxide _______________ 22. Boron trichloride _______________

23. Silicon dioxide _______________ 24. Hydrogen monoiodide _______________

25. Chlorine dioxide _______________ 26. tetraphosphorus

decoxide _______________

27. disulfur trioxide _______________ 28. diPhosphorus trioxide _______________

29. Nitrogen dioxide _______________ 30. Decafluoride disulpher _______________

31. trioxide diarsenic _______________ 32. Sulfur hexafluoride _______________

33. Hydrogen dioxide _______________ 34. Disulpher tetrafluoride _______________

35. Chlorine trifluoride _______________

10th Grade

2nd Term, 2018


Chemistry

42) When The molecular compound can be named as an acid?

43) Complete the following table,

Name Oxyanion (if available)

Formula

HI

HClO3

HClO2

H2SO4

H2S

HNO3

HNO2

H2Se

H3PO4

Hydrobromic acid

Bromose acid

Iodic acid

Hydroflric acid

Chloric acid

Sulforic acid

Hydrochloric acid

10th Grade

2nd Term, 2018


Chemistry

Molecular structures Structural formulas PH3 is a phosphine molecule. Its molecular formula shows that it consists of a phosphorus

atom and three Hydrogen atoms, but this formula does not explain how these four atoms are

bonded. To illustrate how these atoms bonded, one of the following methods can be used.

The previous models reflect the structural forms of the Phosphine compound.

Structural formula: The formula in which symbols and bonds are used to show the relative

positions of atoms.

Molecular formula: A formula that uses symbols and numbers to indicate the types and

numbers of elements involved in the composition of a molecule.

Lewis structures To draw Lewis structures for a specific molecule we follow the following steps,

Step 1: Identify the central atom:

✓ When the molecule contains more than one element, it is necessary to determine which

of these elements will be at the centre of the molecule. The atom of this element is the

lowest in the electronegativity and can be easly identified as it is always far from the

Fluorine element, which is the highest in the electronegativity.

✓ The corresponding table shows the

electronegativity values of a set of elements where

the number below the element is the value of the

electronegativity and shows that the carbon (2.55)

farthest from the Fluorine has a lower

electronegativity than the Nitrogen (3.04) closest

to Fluorine, which in turn has a lower

electronegativity than Oxygen (3.44) because

Oxygen is closer to Fluorine.

✓ Hydrogen is always a side atom.

10th Grade

2nd Term, 2018


Chemistry

Step 2: Identify the bonds created:

1) Determine the number of electrons involved in the formation of bonds, which are, of

course, valence electrons, where we combine all the numbers of valence electrons for

all atoms involved.

2) Determine the number of bonds in the molecule, dividing the number from the previous

step by 2, where each bond is formed by the participation of two electrons (one in each

atom).

3) Put one bond between central atom and each subsidiary atom.

4) Select the number of bonds you've already set and compare them with the number of

bonds you've found in step (2).

5) Determine whether the central atom is bonded to binary or trigonal bonds with some

central atoms or one and draw double or triple bonds as appropriate for the central atom.

Carbon atoms, Oxygen, and Nitrogen are often multi-bonded, while Hydrogen atoms are

only single bonds.

Example,

Draw the Lewis structure for NH3

Step 1: Identify the central atom

The ammonia molecule consists of a Nitrogen atom and three Hydrogen atoms, and the

Nitrogen atom is the central atom.

Step 2: Identify the bonds created

1) Number of electrons involved,

The Nitrogen atom has 5 valence electrons and each Hydrogen atom has a single

equivalence electron.

(3 × 1) + 5 = 8 valence electrons

2) determine the number of bonds in the molecule,

(8 Valence electrons) / (2 electrons for each bond) = 4 bonds

3) Molecule drawing

We have a Nitrogen atom and three Hydrogen atoms

H─N─H│H

4) Calculate the remaining electrons

We have three 3 bonds with six 6 electrons and basically, we have 8 electrons,

leaving a pair of electrons and the final form will be,

. . H─N─H

│H

10th Grade

2nd Term, 2018


Chemistry

Example Draw Lewis' structure for the CO2 molecule.


The molecule consists of a carbon atom and two Oxygen atoms, so the carbon atom

is the central atom.

O C O



The Oxygen atom (in group 16) has six valence electrons,

The carbon atom (group 14) has four valence electrons,

(6 × 2) + 4 = 16 valence electrons



3) Molecule drawing

O = C = O


We have three 4 bonds for eight electrons and basically, we have 16 sixteen

electrons, leaving four pairs of electrons and the final form will be,

. .. .O = C = O . . . .

10th Grade

2nd Term, 2018


Chemistry

Example: Draw the Lewis structure of the ethylene molecule C2H4


The compound consists of two Carbon atoms and four Hydrogen atoms, and the

carbon atoms are in the centre.

HH

CC

HH



The Hydrogen element atom (in group 1) has one equal electron,

The carbon element atom (group 14) has four valence electrons,

(4 × 2) + (1 × 4) = 12 valence electrons



3) Molecule drawing

HH

C = C HH


We have 6 bonds in 12 twelve electrons and basically, we have twelve electrons 12

no pairs of electrons left and the final form will be,

HH

C = C HH

10th Grade

2nd Term, 2018


Chemistry

Lewis structures for polyatomic ions The polyatomic ion is treated as a single-atom ion. The atoms are bonded by covalent bonds.

Because of ion charge, there is a difference in the numbers of valence electrons. In the

positive ions, the valence electrons are lower and, conversely, in the negative ion, the

number of valence electrons is higher.

Example: Draw Lewis structure of phosphate ion PO43-


The molecule consists of a phosphorus atom and four Oxygen atoms, so the

phosphorus atom is the central atom.

O

OPO

O



The Oxygen atom (in group 16) has six valence electrons,

The phosphorus atom (group 15) has four valence electrons,

The ion charge (-3), so we add 3 three more electrons.

32 = (6 × 4) + 5 + 3 valence electrons,

(6 × 4) + 5 + 3 = 32 valence electrons



3) Molecule drawing

O│

O ─ P ─ O │ O


We have four 4 bonds for eight electrons and basically, we have thirty two 32 electrons,

which leaves twenty-four electrons, or 12 pairs of electrons, and the final will be,

. . : O :

. . │ . .

O : ─ P ─ :O . .│

. .

: O :

. .

-3

10th Grade

2nd Term, 2018


Chemistry

44) How many Hydrogen atoms in a molecule phosphine were observed phosphorous PH3? _____________________________________________________________________________________________________________________

45) highlight the ways of expression of phosphine were observed so that bearing the name of the way under the appropriate form. Structural formula * Ball and stick molecular model * Molecular formula * Lewis structure *

Space-filling molecular-model

figure

Expression

46) Fill in the following table for each atom

Atom Group # # Of Valence Electrons Electron Dot Notation # Of Possible Bonds

Ca

Se

Kr

C

Cs

Al

F

P

10th Grade

2nd Term, 2018


Chemistry

47) Draw Lewis structure for the ammonia molecule NH3

48) Draw Lewis structure for BH3

49) Draw Lewis structure for carbon dioxide molecule CO2

10th Grade

2nd Term, 2018


Chemistry

50) Draw Lewis structure for Phosphate ion PO43-

51) Draw Lewis structure for NH4+

52) Draw Lewis structure Lion ClO4-

10th Grade

2nd Term, 2018


Chemistry

Resonance When attempting to draw a Lewis structure for NO3

-nitrate ion we find that there is a range

of possibilities

These possibilities are called resonance forms.

Resonance: A state occurs when there is more probability of drawing a Lewis structure for

the same molecule.

Note,

1) The location of electron pairs varies.

2) The presence of atoms does not change.

3) The bonds converted from single to double bonds and vice versa.

4) The molecule must contain different bonds, single and double.

5) Molecules that contain only single bonds have only one shape - no resonance -.

6) The molecule appears to have only one shape.

7) The lengths of the real bonds are equal to the average of the lengths of the bonds in

the resonance shapes.

Other examples for resonance situations,

O3Ozone

SO2Sulfur

dioxide

NO2-Nitrite

Ion

SO32-Sulfur

ion

10th Grade

2nd Term, 2018


Chemistry

53) Define the resonance.

_____________________________________________________________________________________________________________________

Resonance Structures for a Carbonyl Group

54) How many total electrons are in structures I ( ) and II ( )?

55) Is the total number of electrons in each structure the same? (yes or no)

56) How many single bonds are in structures I ( ) and II ( )?

57) Is the number of single bonds the same in each structure? (yes or no)

58) How many lone pair electrons are in structures I ( ) and II ( )?

59) Is the number of lone pair electrons the same in each structure? (yes or no)

60) How many pi bonds are in structures I ( ) and II ( )?

61) Is the number of pi bonds the same in each structure? (yes or no)

62) Based on the answers above, describe what is different between structures I and II (in

terms of electrons)?

_____________________________________________________________________________________________________________________

63) Is the net charge of structure I the same as the net charge of structure II? (yes or no)

64) What do the curved arrows show in the above structure?

_____________________________________________________________________________________________________________________

65) draw resonance shapes for NO2-

66) draw resonance shapes for SO2

67) draw resonance shapes for O3

68) draw resonance shapes for SO32-

Normally atoms get eight valence electrons when bonded by a covalent bond, but some elements do not follow the Octet rule,

#VE: number of valence electrons

Exceptions to the Octet rule

Odd number of valence electrons Expanded octets

If we want to know how many

bonds are formed in a molecule, we

divide the total number of valence

electrons by 2, which means that

the number of valence electrons

should be an even number.

But some compounds have an odd

total number of valence electrons

and cannot be divided by 2.

#VE Lewis

structure Molecule

17NO2

19ClO2

11NO

Some elements, such as

phosphorus present in group 15,

contains 5 valence electrons, can

share five electrons in the formation

of covalent bonds as in the PCl5

phosphorus pentachloride.

The molecules in which the central

atom is connected to more than four

bonds have more than eight

electrons in its outer shell.

Some compounds reach stability by

less than eight electrons, which are

rare, including the element of boron,

which has three valence electrons

and stabilizes when it has three

bonds, it has only six electrons.

These compounds are reactable

because they can receive a pair of

electrons.

When an atom in a molecule received a pair of electrons from another atom, a bond is formed between two molecules called a Coordinate covalent bond.

Suboctets and coordinate

10th Grade

2nd Term, 2018 Chemistry


69) Write three cases elements do not follow the Octet rule. _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

70) complete the following table with the exception of the Octet rule.

Molecule

Exception

Molecule

Exception

71) What is the name of the phenomenon in the previous figure (between nitrogen, boron)? How composed? _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

10th Grade


http://chemya.weebly.com/ ( 28 )

10th Grade

2nd Term, 2018


Chemistry

Molecular shapes Most of the properties of the compounds depend on how their components are bonded and

on the shape of the molecule. Lewis structures can be used to identify the shape of the

molecule.

The shape of the molecule (molecular geometry) depends on.

1) The way the orbitals of different atoms overlap.

2) Number of shared electrons.

3) Number of unshared electrons (lone pairs).

VSEPR model

Valence Shell Electron Pair Repulsion (VSEPR). It depends on the formation of a shape in

a particular order that will reduce the repulsion to the lowest possible degree between the

pairs of shared and unshared electrons around the central atom.

Bond Angle

When connecting balloons together in different numbers it takes different shapes, these

shapes distinguished by the angles formed between balloons, we find these possibilities,

according to the number of balloons involved form the final.

Likewise, the pairs of electrons that exist around the atoms forming the molecule act as

balloons, forcing them to form certain shapes, separating the central atom from side atoms

by specific angles.

Bond Angle: angle between two lateral atoms and central atom.

The taste of the molecule is controlled by its shape. The taste receptors on the tongue

recognize the taste through the form of food particles. They can distinguish the tastes (salty,

acid, bitter, sweet, monosodium glutamate)

10th Grade

2nd Term, 2018


Chemistry

When linking hybridization with the number of bonds formed we find that

Example# pi bonds# Sigma bondsHybridization

04sp3

13sp2

22sp

The type of hybridization in the compound can be deduced from the number of bonds formed.

For example, in an aluminium chloride compound in which three Chlorine atoms branching

from the central Aluminium atom by three sigma bonds, which resembles a sp2 hybridization.

We always consider the pair of unconnected electrons to be a sigma bond. For example, in

water molecule, consisting of a central oxygen atom and two hydrogen atoms, there are two

Sigma bonds between oxygen and hydrogen with a couple of unshared electrons. That

oxygen is surrounded by four Sigma bonds, so, hybridization in water molecule is sp3.

10th Grade

2nd Term, 2018


Chemistry

Each molecule has its own shape, which depends on the number of shared and unshared

electron pairs as well as on the elements that are associated with the central atom.

10th Grade

2nd Term, 2018


Chemistry

72) Write three variables affecting the shape of the molecule. _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

73) What is the name of the model used to express the shapes of particles? what it based on?

_____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

74) Identify the bond angle.

_____________________________________________________________________________________________________________________

75) What types of taste, which distinguished by the tongue?

_____________________________________________________________________________________________________________________

76) Complete the following table

Examble# π bonds# σ bondsHyberdization

sp3

sp2

sp

77) What is the maximum number of hybrid orbitals could the Carbon atom form? _____________________________________________________________________________________________________________________

78) What is the molecular form for each of the following? (consider that there is no unshared electrons)

Shape Molecule

10th Grade

2nd Term, 2018


Chemistry

79) Complete the following table

Molecular

geometry Hybridization

#

unshared

pairs

#

shared

pairs

#

Electron

pairs

Lewis st. Molecule

BeCl2

AlCl3

CH4

PH3

H2O

80) Whenever the hydrazine molecule (PH3) has the same structure of Aluminum chloride (AlCl3) molecule, consists of a central atom and three terminal atoms but it has a different form, why? _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

81) The bond angle in the water molecule is not 180o, while, water molecule consists of a central atom and two terminal atoms, why? _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

10th Grade

2nd Term, 2018


Chemistry

Electronegativity and polarity

Basic Information About Electronegativity ➢ Fluorine has the highest Electronegativity 3.98 while francium has the lowest 0.7

➢ Most tables do not include values for noble gases because they are often not involved

in reactions.

➢ In the case of an inert gas included in a compound its Electronegativity will be very

high, close to halogens values.

➢ Lanthanides and actinides range from 1.12 to 1.7

➢ As the Electronegativity increases, the atom attraction to the bond electrons increases,

the electrons in the bond are close to the higher Electronegativity atom.

The atoms of the same type attract electrons from both sides equally,

the electrons are present in approximately equal proportions.

The different atoms attract the electrons with different forces, where the electrons are closer to the higher

Electronegativity atom.

Electron affinity Electronegativity

measure of the tendency of an atom to accept an electron

The relative ability of an atom to attract

electrons in a chemical bond Excluding noble gases, it increases with

increasing atomic number within a period.

Decreases with increasing atomic number within a group

Decreases with increasing atomic number within a group

Values were measured Values were assigned

Increases with increasing atomic number within a period.

Electronegativity and Electron affinity

Bond character The bond type depends on the attraction force of the atoms to the bond electrons.

We use the Electronegativity difference between the atoms involved in the formation of the bond to determine the type of bond

between them,

bond typeElectronegativity

difference

Non-polar covalent

(pure covalent) 0

Often covalent Less than 0.4

Polar covalent Between 0.4 and 1.7

Often ionic Greater than 1.7

Affect by the electric field

Location of the bond electronsBond typeThe ratio of

the ionicDifference in the Electronegativity

Types of atoms

Not affectedElectrons evenly distributed

between atoms (H2)pure covalent (non-

polar covalent)ZeroZero

Two atoms of the same type

Not affectedIn the middle of the distance but slightly near the higher

Electronegativity atomcovalent non-polar Between zero

and 5%Between zero

and 0.4

Atoms of different types Affected Near the higher

Electronegativity atom (HI)Covalent

Between 5% and 50%

Between 0.4 and 1.7

Affected Electron moves to the higher atom (NaCl)

IonicGreater than

50%Larger than 1.7

10th Grade



Polarity The electrodes (+ve or -ve) are made up of any material when the charges on the material

differ. For example, the battery carries a positive charge on one end and a negative charge

on the other end and we call it the battery poles.

By the same way, the molecule is polar, ie, has electrodes when one of the ends carries a

positive charge and the other carries a negative charge. When the molecule is from the same

element atoms, the electrons rotate around it in the same way and spend similar times

around the atoms, making them neutral all the time. They do not have poles. Therefore, we

call the bond (non-polar)

Polar Covalent bonds The polar covalent bond is formed when the Electronegativity difference between the atoms

forming the bond is greater than 0.4. The force of attracting bonding electrons by one atom

is larger than the other atom. The electrons spend much longer time around the higher atom

in the Electronegativity making it carry a partial negative charge symbolized by the symbol

(δ-), The other atom carries a positive molecular charge (δ+).

Dipole: The polar bond resulting from the formation of partial charges on atoms forming a

covalent molecule.

Polarity and molecular form The polarity sometimes depends on the shape of the molecule. When comparing the water

molecule (H2O) and the carbon tetrachloride (CCl4) molecule, we find the following,

Carbon tetrachloride (CCl4) Water (H2O)

0.611.24Electronegativity difference

polarpolarBonds Polarity

non-polarpolarMolecule polarity

Geometry

The symmetry (regular shape) of

CCl4 molecule (tetrahedron)

makes equal distribution of the

charges, making the molecule as a

whole acting as neutral, without

molecular charges.

The irregular shape of the water

molecule (bent) makes unequal

distribution of the charges,

forming poles carrying positive

and negative molecular charges.

Interpretation

10th Grade


http://chemya.weebly.com/ ( 36 )

10th Grade

2nd Term, 2018


Chemistry

Solubility of polar molecules

Solubility: The ability of a substance to dissolve in another substance.

What determines the solubility of a molecule?

1) Type of bonding.

2) Shape of the molecule.

The polar and ionic molecules dissolve in water, on the other hand, the

non-polar substances dissolve in non-polar solvents.

properties of covalent compounds The bond between atoms in the molecule is strong, but the intermolecular forces between

the different molecules is rather weak, unlike the bond between ions in ionic compounds,

which is stronger because they are between all the ions of substance in the crystal.

The forces that bind the molecules Van der Waals forces: weak attraction forces between molecules.

Van der Waals forces

Hydrogen bond Dipole-dipole force Dispersion force

It consists of a hydrogen atom at a

dipole of a molecule and an atom

(oxygen, nitrogen or fluorine) at a

dipole of a nearby molecule.

the forces that bind

different partially charged

ends in neighbouring

molecules

A force that binds non-

polar molecules

Stronger than dipole-dipole force Stronger (but still weak) Very weak

Forces and properties Because the forces between molecules in covalent compounds are weak, their melting and

boiling points are low compared to ionic compounds. That is why sugar melt faster than salt

and too many molecular compounds (covalent) in room temperature are in the gaseous

state, such as carbon dioxide (CO2).

Even covalent solid compounds are as soft as paraffin wax, and solids come in a grid similar

to the crystalline network of ionic compounds, but of course they are weaker.

Covalent Network Solids

Covalent Network Solids: substances whose components are

connected by a network of covalent bonds.

They are often brittle and not connecting heat or electricity, but they

are very tough, such as diamonds in which each carbon atom is

attached to four other carbon atoms in a grid, so it forms a strong

crystalline arrangement which has a high melting point.

10th Grade

2nd Term, 2018


Chemistry

82) Compare between Electronegativity and Electron affinity

Electron affinityElectronegativity

Definition

Trend cross group

Trend cross period

How to calculate the value?

83) What is the highest element in the value of Electronegativity? _____________________________________________________________________________________________________________________

84) Electronegativity values for noble gases do not written in some tables, why? _____________________________________________________________________________________________________________________

85) How much the electronegativity value for inert gases when involved in compounds? _____________________________________________________________________________________________________________________

86) To which in the molecule, electrons will be close? _____________________________________________________________________________________________________________________

87) Examine the pictures then answer

Describe the percent of electrons presence around the atoms.

compare Electronegativity in both

cases

Explain the similarity of the atoms in the

molecule, are similar or different?

10th Grade

2nd Term, 2018


Chemistry

88) complete the following table

bond typeElectronegativity difference

0

Less than 0.4

Between 0.4 and 1.7

Greater than 1.7

Use this graph to answer following questions 89) Molecule A has (0) difference in the Electronegativity between the components. describe it. _____________________________________________________________________________________________________________________

90) classify the following molecules, HI: _________________________________________________________________________________________________________________

LiF: ________________________________________________________________________________________________________________

91) What does the symbol (δ) refer to? _____________________________________________________________________________________________________________________

92) defined the Dipolar force. _____________________________________________________________________________________________________________________

Per

cen

t io

nic

ch

ara

cter

75%

50%

25%

3.0 2.0 1.0

Electronegativity difference

LiF

LiI

CaO

HI

HF

CsCl

0.4 1.7 A

10th Grade

2nd Term, 2018


Chemistry

93) Compare between Ammonia molecule (NH3) and Boron trifluoride molecule (BF3).

Boron trifluoride (BF3). Ammonia (NH3)

21.46Electronegativity difference

Bonds Polarity

Molecule polarity

Geometry

Interpretation

94) What determines the solubility of a molecule? _____________________________________________________________________________________________________________________

95) point to the negative atom in the following

C-N C-O C-S C-H 96) in any substance do the polar compound dissolved? _____________________________________________________________________________________________________________________

97) in any substance do the nonpolar compound dissolved? _____________________________________________________________________________________________________________________

98) Compare the forces between the components in a crystalline ionic compound and in a Covalent Network Solids. _____________________________________________________________________________________________________________________

_____________________________________________________________________________________________________________________

10th Grade

2nd Term, 2018


Chemistry

99) What are the forces that bind the molecule components? Describe its strength. _____________________________________________________________________________________________________________________

100) Compare Van der Waals different forces.

Van der Waals forces

101) Sugar melts faster than salt, why? _____________________________________________________________________________________________________________________

102) What are the Covalent Network Solids? _____________________________________________________________________________________________________________________

_____________________________________________________________________________________________________________________

_____________________________________________________________________________________________________________________

103) Write under each of the following if it is polar or nonpolar

10th Grade

2nd Term, 2018


Chemistry

104) List all types of intermolecular forces that would occur in each of the following,

a. CH3CF3 ______________________________________________________

b. CCl4 ______________________________________________________

c. SO2 ______________________________________________________

d. BrF ______________________________________________________

e. (CH3)3N ______________________________________________________

f. PCl5 ______________________________________________________

105) Circle all of the species below that can form a hydrogen bond in its pure form. Explain why the other species couldn't hydrogen bond.

C2H6 CH3NH2 KCl CH3CH2CH2OH CH3OCH3

_____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

_____________________________________________________________________________________________________________________

106) Rank the following compounds from weakest intermolecular forces to strongest. Justify your answers.

H2S I2 N2 H2O _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

107) Rank the following from weakest intermolecular forces to strongest. Justify your answers.

H2Se H2S H2Po H2Te _____________________________________________________________________________________________________________________ _____________________________________________________________________________________________________________________

_____________________________________________________________________________________________________________________

Documents

Covalent Bond - chemya.weebly.comchemya.weebly.com/.../28974683/covalent_bonds_2018.pdf · Single Bond When Single covalent bonds Sometimes atoms need a single electron to reach an