CHAPTER 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… 1s 2 2s 2 2p 2 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 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

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

Valence Electrons and Bonding Patterns Electron configuration of ions Ionic bonds

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

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

Valence Electrons and Bonding Patterns Ionic bonds Write the electron configuration for a magnesium ion (Mg 2+ ). Asked:Electron configuration of Mg 2+ Given: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.

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.

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

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?

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:Ca 2+ and O 2– must combine in a ratio that will balance out the positive and negative charges.

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: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.

Valence Electrons and Bonding Patterns Covalent bonds

Valence Electrons and Bonding Patterns Covalent bonds Valence electrons Unpaired electrons (form bonds) Paired electrons (do NOT form bonds) Lewis dot diagrams Electrons available for bonding

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.

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.

Valence Electrons and Bonding Patterns Covalent bonds

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 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.