Chemical Bonding and Nomenclature Chapter 5 What is a Molecule ? Molecule –A collection of atoms bonded together Elemental molecules –Atoms from same

Chemical Bonding and Nomenclature

Chapter 5

What is a Molecule ?

• Molecule

– A collection of atoms bonded together

• Elemental molecules

– Atoms from same element

• Diatomic: H2, N2, F2 , O2, I2, Cl2 , Br2

• Polyatomic: P4, S8

What is a Molecule

• Molecules of Compounds

– Atoms of different elements

• Simple vs. Complicated

• Small vs. extremely large

Properties of Molecules

• Molecules have different properties than their elemental component.

Element Properties

O Odorless, colorless very reactive toxic gas

H Odorless colorless gas reactive

Properties of Molecules

Molecule Properties

O2Colorless odorless gas moderately reactive not flammable

H2Colorless odorless gas moderately reactive flammable

H2OColorless odorless liquid, low reactivity

H2O2Colorless odorless liquid high reactivity

Why do molecules form?

• To be like the noble gases

– The noble gases are perfect hence they do not react with anything

• They have 8 valence electrons in their outer most shell

Valence Electrons?

• The outermost electrons. Determines the chemical properties of an element

– The only electrons that bond

– The roman numerals at the top of each group A element

– Most elements prefer to have 8 electrons this is called the octet rule. Why?

The Octet Rule

Atoms tend to gain, lose, or share electrons until they have eight valence electrons.

Electron Dot diagrams

• A way of keeping track of valence electrons.

• How to write them– Write the symbol.– Put one dot for each

valence electron– Don’t pair up until you have

too.

X

The Electron Dot diagram for Nitrogen

Nitrogen has 5 valence electrons.

First we write the symbol.

NThen add 1 electron at a time to each side.

Until they are forced to pair up.

Write the electron dot diagram for

• Na• Mg• C• O• F• Al• He

Electron Configurations for Cations

• Metals lose electrons to attain noble gas configuration.

• They make positive ions.

Electron Dots For Cations

• Metals will have few valence electrons

Ca

Electron Dots For Cations• Metals will have few valence electrons• These will come off

Ca

Electron Dots For Cations

• Metals will have few valence electrons• These will come off• Forming positive ions

Ca+2

Electron Configurations for Anions

• Nonmetals gain electrons to attain noble gas configuration.

• They make negative ions.

Electron Dots For Anions

• Nonmetals will have many valence .electrons.

• They will gain electrons to fill outer shell.

P P-3

Stable Electron Configurations

• All atoms react to achieve noble gas configuration.

• Noble gases 8 valence electrons .• Also called the octet rule.

Ar

Covalent Bonding

How does H2 form?

• The nuclei repel

++

How does H2 form?

++

• The nuclei repel

• But they are attracted to electrons

• They share the electrons

Covalent bonds• Nonmetals hold onto their valence

electrons.• They can’t give away electrons to bond.• Still want noble gas configuration.• Get it by sharing valence electrons with

each other.• By sharing both atoms get to count the

electrons toward noble gas configuration.

Covalent bonding

• Fluorine has seven valence electrons

F

Covalent bonding

• Fluorine has seven valence electrons• A second atom also has seven

F F

Covalent bonding

Fluorine has seven valence electrons A second atom also has seven By sharing electrons

F F

Single Covalent Bond

• A sharing of two valence electrons.

• Only nonmetals and Hydrogen.

How to show how they formed• It’s like a jigsaw puzzle.

• I have to tell you what the final formula is.

• You put the pieces together to end up with the right formula.

• For example- show how water is formed with covalent bonds.

Water

H

O

Each hydrogen has 1 valence electron

Each hydrogen wants 1 more

The oxygen has 6 valence electrons

The oxygen wants 2 more

They share to make each other happy

Water• Put the pieces together• The first hydrogen is happy• The oxygen still wants one more

H O

Water• The second hydrogen attaches• Every atom has full energy levels

H OH

Multiple Bonds

• Sometimes atoms share more than one pair of valence electrons.

• A double bond is when atoms share two pair (4) of electrons.

• A triple bond is when atoms share three pair (6) of electrons.

Carbon dioxide• CO2 - Carbon is central

atom ( I have to tell you)

• Carbon has 4 valence electrons

• Wants 4 more• Oxygen has 6 valence

electrons• Wants 2 more

O

C

Carbon dioxide

• Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short

OC

Carbon dioxide Attaching the second oxygen leaves

both oxygen 1 short and the carbon 2 short

OCO

Carbon dioxide

The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO


OCO


OCO


OCO


OCO

Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO


the bond

OCO8 valence electrons


the bond

OCO8 valence electrons


the bond

OCO

8 valence electrons

– Hydrogen 2 valence e-

– Groups 1,2,3 get 2,4,6 valence e-

– Expanded octet more than 8 valence e-

(e.g. S, P, Xe)

– Radicals odd # of valence e-

• Exceptions:

A. Octet Rule

F B FFH O HN O

Very unstable!!

F FF S FF F

B. Drawing Lewis Diagrams• Find total # of valence e-.

• Arrange atoms - singular atom is usually in the middle.

• Form bonds between atoms (2 e-).

• Distribute remaining e- to give each atom an octet (recall exceptions).

• If there aren’t enough e- to go around, form double or triple bonds.

B. Drawing Lewis Diagrams

• CF41 C × 4e- = 4e-

4 F × 7e- = 28e-

32e- FF C F

F

- 8e-

24e-


• BeCl2

1 Be × 2e- = 2e-

2 Cl × 7e- = 14e-

16e-

Cl Be Cl - 4e-

12e-


• CO2

1 C × 4e- = 4e-

2 O × 6e- = 12e-

16e-

O C O - 4e-

12e-

C. Polyatomic Ions

• To find total # of valence e-:– Add 1e- for each negative charge.– Subtract 1e- for each positive charge.

• Place brackets around the ion and label the charge.

C. Polyatomic Ions

• ClO4-

1 Cl × 7e- = 7e-

4 O × 6e- = 24e-

31e- OO Cl O

O

+ 1e-

32e-

- 8e-

24e-

• NH4+

1 N × 5e- = 5e-

4 H × 1e- = 4e-

9e- HH N H

H

- 1e-

8e-

- 8e-

0e-

C. Polyatomic Ions

D. Resonance Structures

• Molecules that can’t be correctly represented by a single Lewis diagram.

• Actual structure is an average of all the possibilities.

• Show possible structures separated by a double-headed arrow.

D. Resonance Structures

OO S O

OO S O

OO S O

SO3

Practice

• Complete the worksheet

Nomenclature-Naming Chemical Compounds

Atoms and ions

• Atoms are electrically neutral.

• Same number of protons and electrons.

• Ions are atoms, or groups of atoms, with a charge.

Atoms and Ions

• Different numbers of protons and electrons.

• Only electrons can move.

• Gain or lose electrons.

Anion

• A negative ion.• Has gained electrons.• Non metals can gain electrons.• Charge is written as a super script on

the right.

F-1 Has gained one electron

O-2 Has gained two electrons

Cations

Positive ions. Formed by losing electrons. More protons than electrons. Metals form cations.

K+1 Has lost one electron

Ca+2 Has lost two electrons

Two Types of Compounds

• Molecular compounds

– Made of molecules.

– Made by joining nonmetal atoms together into molecules.


• Ionic Compounds

– Made of cations and anions.– Metals and nonmetals.– The electrons lost by the cation are gained

by the anion.– The cation and anions surround each

other.– Smallest piece is a FORMULA UNIT.

Formula Unit• The smallest whole number ratio of

atoms in an ionic compound.

• Ions surround each other so you can’t say which is hooked to which.


Smallest piece

Melting Point

State

Types of elements

Formula Unit Molecule

Metal and Nonmetal

Nonmetals

solidSolid, liquid or gas

High >300ºC Low <300ºC

Ionic Molecular

Chemical Formulas

• Shows the kind and number of atoms in the smallest piece of a substance.

• Molecular formula- number and kinds of atoms in a molecule.

• CO2

Charges on ions

• For most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location.

• Elements in the same group have similar properties.

• Including the charge when they are ions.

+2

+1

+3 -3 -2 -1

Naming ions

• We will use the systematic way.

• Cation- if the charge is always the same (Group A) just write the name of the metal.

• Transition metals can have more than one type of charge.– Indicate the charge with roman numerals in

parenthesis.

Name these• Na+1

• Ca+2

• Al+3

• Fe+3

• Fe+2

• Pb+2

• Li+1

Write Formulas for these• Potassium ion• Magnesium ion • Copper (II) ion• Chromium (VI) ion• Barium ion• Mercury (II) ion

Naming Anions

• Anions are always the same.

• Change the element ending to – ide

• F-1 Fluoride

Name these

• Cl-1

• N-3

• Br-1

• O-2

Write these• Sulfide ion

• iodide ion

• phosphide ion

• Strontium ion

Polyatomic ions

• Groups of atoms that stay together and have a charge.– Acetate C2H3O2

-1

– Nitrate NO3-1

– Nitrite NO2-1

– Hydroxide OH-1

– Permanganate MnO4-1

– Cyanide CN-1

Polyatomic ions

• Sulfate SO4-2

• Sulfite SO3-2

• Carbonate CO3-2

• Chromate CrO4-2

• Dichromate Cr2O7-

2

• Phosphate PO4-3

• Phosphite PO3-3

• Ammonium NH4+1

Ions and Ionic Compounds

Naming Binary Ionic Compounds

• Binary Compounds - 2 elements.• Ionic - a cation and an anion.• To write the names just name the two

ions.• Easy with Representative elements.• Group A

• NaCl = Na+ Cl- = sodium chloride

• MgBr2 = Mg+2 Br- = magnesium bromide


• The problem comes with the transition metals.

• Need to figure out their charges.• The compound must be neutral.• same number of + and – charges.• Use the anion to determine the charge

on the positive ion.


• Write the name of CuO• Need the charge of Cu• O is -2• copper must be +2• Copper (II) oxide

• Name CoCl3

• Cl is -1 and there are three of them = -3• Co must be +3 Cobalt (III) chloride


• Write the name of Cu2S.

• Since S is -2, the Cu2 must be +2, so each one is +1.

• copper (I) sulfide• Fe2O3 • Each O is -2 • Fe must be = + 3• iron (III) oxide


• Write the names of the following:

• KCl

• Na3N

• CrN

• Na2Se

Ternary Ionic Compounds

• Will have polyatomic ions• At least three elements• name the ions

• NaNO3

• CaSO4

• CuSO3

• (NH4)2O

Ternary Ionic Compounds

• LiCN

• Fe(OH)3

• (NH4)2CO3

• NiPO4

Writing Formulas

• The charges have to add up to zero.• Get charges on pieces.• Cations from name of table.• Anions from table or polyatomic.• Balance the charges.• Put polyatomics in parenthesis.

Writing Formulas

• Write the formula for calcium chloride.

• Calcium is Ca+2

• Chloride is Cl-1

• Ca+2 Cl-1

• CaCl2

Write the formulas for these• Lithium sulfide• tin (II) oxide• tin (IV) oxide• Magnesium fluoride• Copper (II) sulfate• Iron (III) phosphide• gallium nitrate• Iron (III) sulfide

Write the formulas for these

• Ammonium chloride

• ammonium sulfide

• barium nitrate

Things to look for

• If cations have (), the number is their charge.

• If anions end in -ide they are probably off the periodic table (Monoatomic)

• If anion ends in -ate or -ite it is polyatomic

Molecular Compounds

Molecular compounds

• made of just nonmetals

• smallest piece is a molecule

• can’t be held together because of opposite charges

• can’t use charges to figure out how many of each atom

Easier

• Ionic compounds use charges to determine how many of each

– Have to figure out charges

– Have to figure out numbers

• Molecular compounds name tells you the number of atoms

– Uses prefixes to tell you the number

Prefixes

• 1 mono-• 2 di-• 3 tri-• 4 tetra-• 5 penta-• 6 hexa-• 7 hepta-• 8 octa-

Prefixes

• 9 nona-

• 10 deca-

• One exception is we don’t write mono- if there is only one of the first element.

Name These

• N2O

• NO2

• Cl2O7

• CBr4

• CO2

• BaCl2

Write formulas for these

• diphosphorus pentoxide• tetraiodide nonoxide• sulfur hexaflouride• nitrogen trioxide• Carbon tetrahydride• phosphorus trifluoride• aluminum chloride

Naming Acids

a little tricky so pay attention

Acids• Compounds that give off hydrogen ions

when dissolved in water

• Must have H in them (somewhere)

• will always be some H next to an anion

• The anion determines the name.

Naming acids• If the anion attached to hydrogen ends in -ide, put the

prefix hydro- and change -ide to -ic acid

• HCl - hydrogen ion and chloride ion

• hydrochloric acid

• H2S hydrogen ion and sulfide ion

• hydrosulfuric acid

Naming Acids

• If the anion has oxygen in it• it ends in -ate or -ite• change the suffix -ate to -ic acid

• HNO3 Hydrogen and nitrate ions

• Nitric acid• change the suffix -ite to -ous acid

• HNO2 Hydrogen and nitrite ions

• Nitrous acid

Name these

• HF

• H3P

• H2SO4

• H2SO3

• HCN

• H2CrO4

•

Writing Formulas

• Hydrogen will always be first

• name will tell you the anion

• make the charges cancel out.

• Starts with hydro- no oxygen, -ide

• no hydro, -ate comes from -ic, -ite comes from -ous

Write formulas for these

• hydroiodic acid• acetic acid• carbonic acid• phosphorous acid• hydrobromic acid• Perchloric acid• Dichromic acid• Oxalic acid

Documents

Chemical Bonding and Nomenclature Chapter 5 What is a Molecule ? Molecule –A collection of atoms bonded together Elemental molecules –Atoms from same