CHEMICAL BONDSCHEMICAL BONDS

CHAP 9CHAP 9

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Homework for Chap 9Homework for Chap 9

Read p 231 – 249

Applying the Concepts # 1 – 21

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Compounds and Chemical ChangeCompounds and Chemical Change

1.1. ElementsElements are composed of extremely small particles are composed of extremely small particles called called atomsatoms. .

2.2. CompoundsCompounds are composed of atoms of more than one are composed of atoms of more than one element held together by element held together by chemical bondschemical bonds..

3. MoleculeMolecule – smallest particle of a compound that can – smallest particle of a compound that can

exist and still retain characteristic chemical properties exist and still retain characteristic chemical properties

4. Compounds occur as solids, liquids, and gases

Fig. 9.2 Common gases exist as atoms or molecules

Fig. 9.3Example of a

chemical reactionchemical reaction

Burning magnesium (Mg)

in air

to produce magnesium oxide

(“milk of magnesia”)

Energy is released

Fig. 9.4 (A) Photosynthesis stores solar energy

Fig. 9.4 (B) Combustion releases solar energy

Reactants Products

Fig 8.20 Electron dot notation for representative

elements1

5 6 7

8

3 42

Valence electronsValence electrons – outermost electrons in an atomOctet ruleOctet rule – atoms attempt to acquire 8 valence electrons

Fig. 9.5

energy + Na → Na+ + e−

energy + Ca →

energy + Al →

5 6 7

8

3 4

1

2

Ca2+ + e−

Al3+ + e−

Fig 8.21

Three Types of Chemical BondsThree Types of Chemical Bonds(1) Ionic bonds

• Electrons are transferred from one atom to another

• Occur between a metal atom and a nonmetal atom

(2) Covalent bonds

• Electrons are shared between two atoms• Occur between two nonmetal atoms

(3) Metallic bonds

• Metal atoms share many electrons in a “sea” that is free to move throughout the metal

Na 11 protons11 electrons Na+ 11 protons

10 electrons

Cl 17 protons17 electrons

Cl-17 protons18 electrons

Formation of an ionic bond

+ e−

Net reaction: Na + Cl → Na+Cl− + energy

This energy is called the heat of formation

Fig. 9.6 Model of the sodium chloride crystal

−+

No molecules in an ionic compound!No molecules in an ionic compound!

Na+ ionsCl− ions

Formula unit

Fig. 9.7 The cubic crystal structure of sodium chloride

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• Ionic compounds consist of a combination of positive ions and negative ions

• Ions are formed as nonmetal atoms gain and metal atoms lose electrons to achieve stable noble gas structure

• The sum of the charges on the positive ions and negative ions in each formula unit must equal zero

• How do we determine the formula for an ionic compound?

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Formula of Ionic Compounds

Al2O3

2 x +3 = +6 3 x -2 = -6

Al3+ O2-

CaBr2

1 x +2 = +2 2 x -1 = -2

Ca2+ Br-

Al and O

Ca and Br