0.5 What are the objects around us made of  (Page 3/3)

This website allows you to view several molecules. You do not need to know these molecules, this is simply to allow you to see one way ofrepresenting molecules.

Atoms and molecules

1. In each of the following, say whether the chemical substance is made up of single atoms, simple molecules or giant molecules.
   1. ammonia gas ( ${\mathrm{NH}}_3$ )
   2. zinc metal ( $\mathrm{Zn}$ )
   3. graphite ( $\mathrm{C}$ )
   4. nitric acid ( ${\mathrm{HNO}}_3$ )
   5. neon gas ( $\mathrm{He}$ )
2. 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 simple or giant molecule?
3. Represent each of the following molecules using its chemical formula , structural formula and ball and stick model .
   1. Hydrogen
   2. Ammonia
   3. sulphur dioxide

Summary

• The smallest unit of matter is the atom . Atoms can combine to form molecules .
• A compound is a group of two or more atoms that are attracted to each other by chemical bonds.
• A small molecule consists of a few atoms per molecule. A giant molecule consists of millions of atoms per molecule, for example metals and diamonds.
• The structure of a molecule can be represented in a number of ways.
• The chemical formula of a molecule is an abbreviated way of showing a molecule, using the symbols forthe elements in the molecule. There are two types of chemical formulae: molecular and empirical formula.
• The molecular formula of a molecule gives the exact number of atoms of each element that are in the molecule.
• The empirical formula of a molecule gives the relative number of atoms of each element in the molecule.
• Molecules can also be represented using diagrams .
• A ball and stick diagram is a 3-dimensional molecular model that uses 'balls' to represent atomsand 'sticks' to represent the bonds between them.
• A space-filling model is also a 3-dimensional molecular model. The atoms are represented by spheres.
• In a molecule, atoms are held together by chemical bonds or intramolecular forces . Covalent bonds, ionic bonds and metallic bonds are examples of chemical bonds.
• A covalent bond exists between non-metal atoms. An ionic bond exists between non-metal and metal atoms and a metallic bond exists between metal atoms.
• Intermolecular forces are the bonds that hold molecules together.

End of chapter exercises

1. 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.
2. Give a definition for each of the following terms: descriptions.
   1. molecule
   2. Ionic compound
   3. Covalent network structure
   4. Empirical formula
   5. Ball-and-stick model
3. Ammonia, an ingredient in household cleaners, can be broken down to form one part nitrogen ( $\mathrm{N}$ ) and three parts hydrogen ( $\mathrm{H}$ ). This means that ammonia...
   1. is a colourless gas
   2. is not a compound
   3. cannot be an element
   4. has the formula ${\mathrm{N}}_3\mathrm{H}$
4. Represent each of the following molecules using its chemical formula, its structural formula and the ball-and-stick model:
   1. nitrogen
   2. carbon dioxide
   3. methane
   4. argon