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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.