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CHAPTER 7. Bonding. 7.2 Valence Electrons and Bonding Patterns. What we have seen so far…. Valence electrons are responsible for chemical bonding. What we have seen so far…. Valence electrons are responsible for chemical bonding.

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slide1

CHAPTER 7

Bonding

7.2 Valence Electrons and Bonding Patterns

slide2

What we have seen so far…

Valence electrons are responsible for chemical bonding.

slide3

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

1s22s22p2

4 valence electrons

slide4

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

slide6

The octet rule

Oxygen ends up with 8 valence electrons.

slide7

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.

slide9

Ionic bonds

Electron configuration of ions

8 valence electrons

slide10

Ionic bonds

Electron configuration of ions

Same configuration as neon (a noble gas)

slide11

Ionic bonds

Electron configuration of ions

slide12

Ionic bonds

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

slide13

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.

slide14

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.

slide15

Ionic formulas

Ionic substances typically form crystals.

A crystal is a large group of oppositely charged ions arranged in a regular pattern.

slide16

Ionic formulas

Total charge of zero

Calcium chloride, CaCl2

Two chloride ions for each calcium

slide17

Ionic formulas

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

slide18

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.

slide19

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.

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Covalent bonds

Unpaired electrons

(form bonds)

Paired electrons

(do NOT form bonds)

Lewis dot diagrams

Valence electrons

3 4 5 6

Electrons available

for bonding

3 4 3 2

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Covalent bonds

All atoms have 1 bond.

All atoms have 4 bonds.

All atoms have 2 bonds.

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

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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.

slide25

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.