INTRODUCTION TOCHEMICAL BONDS

A general comparison of metals and nonmetals.

Chemical Bonds

Types of Chemical Bonding

1. Metal with nonmetal:

electron transfer and ionic bonding

2. Nonmetal with nonmetal:

electron sharing and covalent bonding

3. Metal with metal:

electron pooling and metallic bonding

Chemical Bonds

The three models of chemical bonding.

Chemical Bonds

Lewis Electron-Dot Symbols

For main group elements -

Example:

Nitrogen, N, is in Group 5A and therefore has 5 valence electrons.

N:

.

..

:

N .. .

.N :.

.

:N ...

The A group number gives the number of valence electrons.

Place one dot per valence electron on each of the four sides of the element symbol.

Pair the dots (electrons) until all of the valence electrons are used.

Chemical Bonds

Lewis electron-dot symbols for elements in Periods 2 and 3.

Chemical Bonds

Electron configurations

Li 1s22s1

Orbital diagrams

Lewis electron-dot symbols

+ F 1s22s22p5 Li+ 1s2 + F- 1s22s22p6

Three ways to represent the formation of Li+ and F- through electron transfer.

Li

1s 2s 2p

F

1s 2s 2p

+

Li+

1s 2s 2p

F-

1s 2s 2p

+

.

+ F: ::Li . Li+ + F -::

::

Ionic Bonds

Ionic Bonds

Electron configurations

Li 1s22s1

Orbital diagrams

Lewis electron-dot symbols

+ O 1s22s22p4 Li+ 1s2 + O-2 1s22s22p6

Three ways to represent the formation of Li+ and O-2 through electron transfer.

Li

1s 2s 2p

O

1s 2s 2p

+

Li+

1s 2s 2p

O-2

1s 2s 2p

+

+ O: ::2Li . 2Li+ + O -::

::

Ionic Bonds

Li+

1s 2s 2p

Use condensed electron configuration and Lewis electron dot symbols to depict the monatomic ions formed from each of the following atoms, and predict the formula of the compound the ions produced:

a) Ba and Cl

b) Sr and O

c) Al and F

d) Rb and O

Answers: a) BaCl2b) SrOc) AlF3

d) Rb2O

Sample Problem

Worksheet #4-0.1

Use Lewis electron dot symbols to depict the ionic compounds formed from each of the following atoms.

1. Calcium and phosphorus

2. Aluminum and oxygen

3. Magnesium and chlorine

3-11

A bond created by the sharing of electrons between atoms

Occurs between two nonmetals (resulting in a neutral overall charge)

Electrons typically shared in pairs

Weaker bonds than ionic bonds

Figure 8.2

3-12

When two nonmetals form a bond, the bond is covalent. They are both close to the noble-gas electron configuration, so sharing will allow both to obtain it.

In a covalent bond, each shared electron interacts simultaneously with two nuclei.

Figure 8.12

3-13

The atoms of CO2 molecules are held together by strong covalent bonds. No bonds connect the molecules, so CO2 molecules separate from each other into the gas state at room temperature.

Figure 8.13 Figure from p. 28

3-14

Just as in ionic bonding, covalent bonds are formed so that each atom can have the noble-gas electron configuration.

Noble gases have 8 valence electrons, an octet.

Figure 8.14

3-15

Octet rule - tendency of an atom to achieve an electron configuration having 8 valence electrons

▪ Covalently bonded atoms achieve 8 valence electrons by sharing electrons

▪ The 8 electrons exist in 4 pairs

3-16

How does hydrogen obtain a noble-gas electron configuration?

H atoms bond with other atoms to obtain a total of 2 electrons like He.

3-17

Do the atoms in each of these molecules have an octet?

Why do the halogens exist as diatomic molecules?

Figure 8.16

3-18

How many valence electrons does an oxygen atom have?

How many does it need to obtain an octet?

O2 has a double bond, two pairs of shared electrons

Figure 8.17

Multiple Bonds

3-19

How many valence electrons does a nitrogen atom have?

How many does it need to obtain an octet?

N2 has a triple bond, three pairs of shared electrons

3-20

How do phosphorus and sulfur obtain an octet in P4 and S8?

3-218-21

How many bonds do each of the following atoms tend to form?

a) H

b) Cl

c) O

d) N

e) C

1

1

2

3

4

3-228-22

Draw the Lewis structures for each of the following based on the number of bonds that each tends to form. Remember to include the nonbonding electrons so that all have octets (except H).

1. C2H6

2. C2H4

3. C2H2

4. HCN

Sample Problem: Answers

3-238-23

Worksheet #4-0.2

Draw the Lewis structures for each of the following based on the number of bonds that each tends to form.1. CO2

2. H2S3. O3

4. SO2

5. NNO

Electronegativity

Electronegativity - The tendency of an atom in a molecule to attract electrons to itself

The Pauling electronegativity (EN) scale.

Electronegativity

Electronegativity and atomic size.

Electronegativity

Electronegativity

Using the periodic table only, arrange the elements in each set in order of increasing EN:

a) S, O, Sib) Ca, P, As

Answer: a) Si < S < Ob) Ca < As < P

Sample Problem

Worksheet #4-0.3

Arrange the following elements in order of increasing electronegativities.

1. Cl , At, Br, F, I

2. Al, Cs, Mg, P

3. O, P, S, Si

4. Mg, Be, C, Ca

5. Br, In, Te, Rb

Figure 9.21 Electron density distributions in H2, F2, and HF.

Electronegativity

DEN

3.0

2.0

0.0

Boundary ranges for classifying ionic character of chemical bonds.

Electronegativity

Percent ionic character of electronegativity difference (DEN).

Electronegativity

Properties of the Period 3 chlorides.

Electronegativity

Figure 9.25 Electron density distributions in bonds of the Period 3 chlorides.

Electronegativity

Are the bonds in each of the following substances ionic,nonpolar covalent or polar covalent? Arrange the substanceswith polar covalent bonds in order of increasing bond polarity:a) S8 d) SCl2b) RbCl e) F2

c) PF3 f) SF2

Answers: a) nonpolar covalentb) ionicc) polar covalentd) polar covalente) nonpolar covalentf) polar covalent

SCl2 < SF2 < PF3

Sample Problem

Worksheet #4-0.4

Arrange the bonds in each of the following sets in

increasing polarity.

1. HBr, HF, HI, H2 , HCl

2. Cl2, BeCl2, BrCl, BCl3

3. H2S, PH3, AsCl3, SbCl3

4. CCl4, CF4, CBr4, CI4

5. H2S, H2O, H2Se, H2Te