Diamonds are most often thought of in terms of their use in thejewellery industry. However, about 80% of mined diamonds are unsuitable for use
as gemstones and are therefore used in industry because of their strength andhardness. These properties of diamonds are due to the strong covalent bonds
(covalent bonding will be explained later) between the carbon atoms in diamond.The most common uses for diamonds in industry are in cutting, drilling,
grinding, and polishing.
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
In each of the following, say whether the chemical
substance is made up of single atoms, simple molecules or giant molecules.
ammonia gas (
)
zinc metal (
)
graphite (
)
nitric acid (
)
neon gas (
)
Refer to the diagram below and then answer the
questions that follow:
Identify
the molecule.
Write the molecular formula for the molecule.
Is the molecule a simple or giant molecule?
Represent each of the following molecules using its
chemical formula ,
structural formula and
ball and stick model .
Hydrogen
Ammonia
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
Give one word or term for each of the following
descriptions.
A composition of two or more atoms that act as a unit.
Chemical formula that gives the relative number of atoms
of each element that are in a molecule.
Give a definition for each of the following terms:
descriptions.
molecule
Ionic compound
Covalent network structure
Empirical formula
Ball-and-stick model
Ammonia, an ingredient in household cleaners, can be broken down to
form one part nitrogen (
) and three parts hydrogen (
). This means that
ammonia...
is a
colourless gas
is not a compound
cannot be an element
has the formula
Represent each of the following molecules using its chemical formula, its structural formula and the ball-and-stick model: