# 0.4 Chemical bonding  (Page 7/9)

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## Activity: building models

Using coloured balls and sticks (or any other suitable materials) build models of each type of bonding. Think about how to represent each kind of bonding. For example, covalent bonding could be represented by simply connecting the balls with sticks to represent the molecules, while for ionic bonding you may wish to construct part of the crystal lattice. Do some research on types of crystal lattices (although the section on ionic bonding only showed the crystal lattice for sodium chloride, many other types of lattices exist) and try to build some of these. Share your findings with your class and compare notes to see what types of crystal lattices they found. How would you show metallic bonding?

You should spend some time doing this activity as it will really help you to understand how atoms combine to form molecules and what the differences are between the types of bonding.

## Chemical bonding

1. Give two examples of everyday objects that contain..
1. covalent bonds
2. ionic bonds
3. metallic bonds
2. Complete the table which compares the different types of bonding:
 Covalent Ionic Metallic Types of atoms involved Nature of bond between atoms Melting Point (high/low) Conducts electricity? (yes/no) Other properties
3. Complete the table below by identifying the type of bond (covalent, ionic or metallic) in each of the compounds:
 Molecular formula Type of bond $\mathrm{H}{}_{2}\mathrm{SO}{}_{4}$ $\mathrm{FeS}$ $\mathrm{NaI}$ $\mathrm{MgCl}{}_{2}$ $\mathrm{Zn}$
4. Which of these substances will conduct electricity most effectively? Give a reason for your answer.
5. Use your knowledge of the different types of bonding to explain the following statements:
1. Swimming during an electric storm (i.e. where there is lightning) can be very dangerous.
2. Most jewellery items are made from metals.
3. Plastics are good insulators.

## The formulae of covalent compounds

To work out the formulae of covalent compounds, we need to use the valency of the atoms in the compound. This is because the valency tells us how many bonds each atom can form. This in turn can help to work out how many atoms of each element are in the compound, and therefore what its formula is. The following are some examples where this information is used to write the chemical formula of a compound.

Write the chemical formula for water

1. A molecule of water contains the elements hydrogen and oxygen .

2. The valency of hydrogen is 1 and the valency of oxygen is 2. This means that oxygen can form two bonds with other elements and each of the hydrogen atoms can form one.

3. Using the valencies of hydrogen and oxygen, we know that in a single water molecule, two hydrogen atoms will combine with one oxygen atom. The chemical formula for water is therefore:

$\mathrm{H}{}_{2}\mathrm{O}$ .

Write the chemical formula for magnesium oxide

1. A molecule of magnesium oxide contains the elements magnesium and oxygen .

2. The valency of magnesium is 2, while the valency of oxygen is also 2. In a molecule of magnesium oxide, one atom of magnesium will combine with one atomof oxygen.

3. The chemical formula for magnesium oxide is therefore:

$\mathrm{MgO}$

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