CHAPTER 7

7.2 Valence Electrons and

Bonding Patterns

Bonding

2 7.2 Valence Electrons and Bonding Patterns

What we have seen so far…

Valence electrons are responsible for chemical bonding.

3 7.2 Valence Electrons and Bonding Patterns

What we have seen so far…

1s22s22p2

4 valence electrons

Lewis dot diagram for carbon

Valence electrons are responsible for chemical bonding.

The Lewis dot diagram represents each valence electron as a dot around the atom symbol.

4 7.2 Valence Electrons and Bonding Patterns

What we have seen so far…

Difference in electronegativity

= 0.89

Valence electrons are responsible for chemical bonding.

The Lewis dot diagram represents each valence electron as a dot around the atom symbol.

Electronegativity helps to determine the bond type.

5 7.2 Valence Electrons and Bonding Patterns

6 7.2 Valence Electrons and Bonding Patterns

The octet rule

Oxygen ends up with 8 valence electrons.

7 7.2 Valence Electrons and Bonding Patterns

octet rule: rule that states that elements transfer or share electrons in chemical bonds to reach a stable configuration of eight valence electrons.

H, Li, Be, and B form

bonds to reach two

valence electrons.

8 7.2 Valence Electrons and Bonding Patterns

Ionic bonds

9 7.2 Valence Electrons and Bonding Patterns

Electron configuration of ions

Ionic bonds

8 valence electrons

10 7.2 Valence Electrons and Bonding Patterns

Electron configuration of ions

Ionic bonds

Same configuration as neon (a noble gas)

11 7.2 Valence Electrons and Bonding Patterns

Electron configuration of ions

Ionic bonds

12 7.2 Valence Electrons and Bonding Patterns

Ionic bonds

Write the electron configuration for a magnesium ion (Mg2+).

13 7.2 Valence Electrons and Bonding Patterns

Ionic bonds

Write the electron configuration for a magnesium ion (Mg2+).

Asked: Electron configuration of Mg2+

Given: Mg, atomic number of 12, charge of +2

Relationships: The electron configuration of magnesium is 1s22s22p63s2.

14 7.2 Valence Electrons and Bonding Patterns

Ionic bonds

Write the electron configuration for a magnesium ion (Mg2+).

Asked: Electron configuration of Mg2+

Given: Mg, atomic number of 12, charge of +2

Relationships: The electron configuration of magnesium is 1s22s22p63s2.

Solve: Mg must lose two electrons to become Mg2+. Therefore it loses the pair of 3s2 electrons.

Answer: The electron configuration of Mg2+ is 1s22s22p6, which is identical to neon.

15 7.2 Valence Electrons and Bonding Patterns

Ionic formulas

Ionic substances typically form crystals.

A crystal is a large group

of oppositely charged ions

arranged in a regular

pattern.

16 7.2 Valence Electrons and Bonding Patterns

Ionic formulas

Total charge of zero

Calcium chloride, CaCl2

Two chloride ions for each calcium

17 7.2 Valence Electrons and Bonding Patterns

Ionic formulas

What is the correct formula for calcium oxide, a compound used in making paper and pottery, and adjusting the pH of soils?

18 7.2 Valence Electrons and Bonding Patterns

Ionic formulas

What is the correct formula for calcium oxide, a compound used in making paper and pottery, and adjusting the pH of soils?

Asked: The formula for the ionic compound calcium oxide

Given: Calcium oxide is made from calcium and oxygen ions. Calcium forms +2 ions and oxygen forms –2 ions.

Relationships: Ca2+ and O2– must combine in a ratio that will balance out the positive and negative charges.

19 7.2 Valence Electrons and Bonding Patterns

Ionic formulas

What is the correct formula for calcium oxide, a compound used in making paper and pottery, and adjusting the pH of soils?

Asked: The formula for the ionic compound calcium oxide

Given: Calcium oxide is made from calcium and oxygen ions. Calcium forms +2 ions and oxygen forms –2 ions.

Relationships: Ca2+ and O2– must combine in a ratio that will balance out the positive and negative charges.

Solve: The charge on one Ca2+ ion will balance out with the charge on one O2– ion. Therefore the ratio is 1:1 and the formula is CaO.

20 7.2 Valence Electrons and Bonding Patterns

Covalent bonds

21 7.2 Valence Electrons and Bonding Patterns

Covalent bonds

3 4 5 6Valence

electrons

Unpaired electrons

(form bonds)Paired electrons

(do NOT form bonds)

Lewis dot diagrams

Electrons available

for bonding3 4 3 2

22 7.2 Valence Electrons and Bonding Patterns

All atoms have 1 bond.

All atoms have 4 bonds.

All atoms have 2 bonds.

Covalent bonds

All atoms of the same element form the same number of bonds.

23 7.2 Valence Electrons and Bonding Patterns

Covalent bonds

Bonds form in such a way that each atom in the

compound achieves the same number of valence

electrons as the closest noble gas atom.

24 7.2 Valence Electrons and Bonding Patterns

Covalent bonds

25 7.2 Valence Electrons and Bonding Patterns

octet rule: rule that states that elements transfer or share electrons in chemical bonds to reach a stable configuration of eight valence electrons.

Covalent bondsElectrons are transferred so that each element has 8 valence

electrons and has the same configuration as the closest noble gas.

The light elements H, Li, Be, and B prefer to have 2 valence electrons.

Ion formationAtoms gain or lose one or more electrons to reach the same electron

configuration as the closest noble gas, with 8 valence electrons.