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## End of chapter exercises

Give one word or term for each of the following descriptions.

1. A composition of two or more atoms that act as a unit.

2. Chemical formula that gives the relative number of atoms of each element that are in a molecule.

a) Molecule.

b) Empirical formula.

Give a definition for each of the following terms:

1. molecule

2. ionic compound

3. covalent network structure

4. empirical formula

5. ball-and-stick model

a) A group of two or more atoms that are attracted to each other by chemical bonds

b) An ionic compound is an ionically bonded substance. Ionic compounds have ionic bonds and consist of a metal and a non-metal.

c) A giant lattice of covalently bonded molecules such as graphite.

d) A formula giving the relative number of atoms of each element in a molecule.

e) A means of representing a molecule graphically. Elements are shown as balls and the bonds between them are represented by lines or 'sticks'.

Ammonia, an ingredient in household cleaners, is made up of one part nitrogen ($N$) and three parts hydrogen ($H$). Answer the following questions:

1. is ammonia a covalent, ionic or metallic substance?

2. write down the molecular formula for ammonia

3. draw a ball-and-stick diagram

4. draw a space-filling diagram

a) covalent

b) ${\text{NH}}_{3}$

c)

d)

In each of the following, say whether the chemical substance is made up of covalent, molecular structures, covalent network structures, ionic network structures or metallic structures:

1. ammonia gas ($NH 3$)

2. zinc metal ($Zn$)

3. graphite ($C$)

4. nitric acid ($HNO 3$)

5. potassium bromide ($KBr$)

a) covalent molecular structure

b) metallic network structure

c) covalent network structure

d) covalent molecular structure

e) Ionic network structure

Refer to the diagram below and then answer the questions that follow:

1. Identify the molecule.

2. Write the molecular formula for the molecule.

3. Is the molecule a covalent, ionic or metallic substance? Explain.

a) Carbon dioxide. (There is one carbon and two oxygen atoms.)

b) $C{O}_{2}$

c) Covalent substance. The electronegativity difference between C and O is 0.89 so the C and O are covalently bonded.

Represent each of the following molecules using its chemical formula, structural formula and the ball-and-stick model.

1. nitrogen

2. carbon dioxide

3. methane

4. argon

a) Chemical formula: ${N}_{2}$

structural formula:

ball-and-stick model:

b) Chemical formula: $C{O}_{2}$

structural formula:

ball-and-stick model:

c) Chemical formula: $C{H}_{4}$

structural formula:

ball-and-stick model:

d) Chemical formula: $Ar$

structural formula:

Ar

ball-and-stick model: