7.2 Valence
Electrons and
Bonding Patterns

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Valence electrons are responsible for chemical bonding.
What we have seen so far…
7.2 Valence Electrons and Bonding Patterns

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What we have seen so far…
Valence electrons are responsible for chemical bonding.
The Lewis dot diagram represents each valence electron as a dot around the atom symbol.
Lewis dot diagram for carbon
1s 2 2s 2 2p 2
4 valence electrons
7.2 Valence Electrons and Bonding Patterns

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What we have seen so far…
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.
Difference in electronegativity
= 0.89
7.2 Valence Electrons and Bonding Patterns

‹#› 7.2 Valence Electrons and Bonding Patterns

The octet rule
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Oxygen ends up with 8 valence electrons .
7.2 Valence Electrons and Bonding Patterns

H, Li, Be, and B form bonds to reach two valence electrons .
‹#› octet rule: rule that states that elements transfer or share electrons in chemical bonds to reach a stable configuration of eight valence electrons .
7.2 Valence Electrons and Bonding Patterns

Ionic bonds
‹#› 7.2 Valence Electrons and Bonding Patterns

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Electron configuration of ions
Ionic bonds
8 valence electrons
7.2 Valence Electrons and Bonding Patterns

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Electron configuration of ions
Ionic bonds
Same configuration as neon (a noble gas)
7.2 Valence Electrons and Bonding Patterns

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Electron configuration of ions
Ionic bonds
7.2 Valence Electrons and Bonding Patterns

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Ionic bonds
Write the electron configuration for a magnesium ion (Mg 2+ ).
7.2 Valence Electrons and Bonding Patterns

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Ionic bonds
Write the electron configuration for a magnesium ion (Mg 2+ ).
Asked:
Given:
Electron configuration of Mg 2+
Mg, atomic number of 12, charge of +2
Relationships: The electron configuration of magnesium is 1s 2 2s 2 2p 6 3s 2 .
7.2 Valence Electrons and Bonding Patterns

Ionic bonds
Write the electron configuration for a magnesium ion (Mg 2+ ).
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Asked:
Given:
Electron configuration of Mg 2+
Mg, atomic number of 12, charge of +2
Relationships: The electron configuration of magnesium is 1s 2 2s 2 2p 6 3s 2 .
Solve: Mg must lose two electrons to become Mg 2+ .
Therefore it loses the pair of 3s 2 electrons.
Answer: The electron configuration of Mg 2+ is 1s 2 2s 2 2p 6 , which is identical to neon.
7.2 Valence Electrons and Bonding Patterns

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Ionic substances typically form crystals .
Ionic formulas
A crystal is a large group of oppositely charged ions arranged in a regular pattern.
7.2 Valence Electrons and Bonding Patterns

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Ionic formulas
Total charge of zero
Calcium chloride, CaCl
2
Two chloride ions for each calcium
7.2 Valence Electrons and Bonding Patterns

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Ionic formulas
What is the correct formula for calcium oxide, a compound used in making paper and pottery, and adjusting the pH of soils?
7.2 Valence Electrons and Bonding Patterns

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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: Ca 2+ and O 2
– must combine in a ratio that will balance out the positive and negative charges.
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?
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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: Ca 2+ and O 2
– must combine in a ratio that will balance out the positive and negative charges.
Solve: The charge on one Ca 2+ ion will balance out with the charge on one O 2 – ion. Therefore the ratio is 1:1 and the formula is
CaO.
7.2 Valence Electrons and Bonding Patterns

Covalent bonds
‹#› 7.2 Valence Electrons and Bonding Patterns

Lewis dot diagrams
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Valence electrons
Electrons available for bonding
3
3
Unpaired electrons
(form bonds)
Covalent bonds
Paired electrons
(do NOT form bonds)
4
4
5
3
6
2
7.2 Valence Electrons and Bonding Patterns

Covalent bonds
All atoms have 1 bond.
All atoms have 4 bonds.
All atoms have 2 bonds.
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All atoms of the same element form the same number of bonds.
7.2 Valence Electrons and Bonding Patterns

Covalent bonds
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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.
7.2 Valence Electrons and Bonding Patterns

Covalent bonds
‹#› 7.2 Valence Electrons and Bonding Patterns

Covalent bonds
Electrons 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 formation
Atoms gain or lose one or more electrons to reach the same electron configuration as the closest noble gas, with 8 valence electrons.
octet rule: rule that states that elements transfer or share electrons in chemical bonds to reach a stable configuration of eight valence electrons .
‹#› 7.2 Valence Electrons and Bonding Patterns