2.
3 Why elements react to form compounds
2.3 Why elements react
to form compounds
2.3A Atoms and ions
Focus
This exercise will help you to show the difference between an atom and
an ion.
1 This diagram shows the structure of a lithium atom. Label the
electron shell with the highest energy level.
2 Draw a diagram to show the structure of a lithium ion.
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2 Properties of materials
3 The symbol for a lithium atom is Li. What is the symbol for a
lithium ion?
4 This diagram shows the structure of a fluorine atom.
Draw a diagram to show the structure of a fluorine ion.
5 The symbol for a fluorine atom is F. What is the symbol for a
fluorine ion?
2.3B Why do ions form?
Practice
In this exercise you will practice drawing atoms and ions and explain
why ions form.
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2.3 Why elements react to form compounds
1 Using the information here, draw atoms and ions of sodium and
chlorine in the spaces below.
sodium chlorine
atomic number 11 atomic number 17
mass number 23 mass number 35
sodium atom: chlorine atom:
sodium ion: chlorine ion:
2 How are the electrons in an atom held in place?
3 Why are ions formed?
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2 Properties of materials
2.3C Forming ionic compounds.
Challenge
In this exercise you will draw diagrams to illustrate the formation of
ionic compounds.
1 When calcium reacts with chlorine the compound calcium chloride
is formed. The formula for calcium chloride is CaCl2.
Information you may need:
Calcium has an atomic number of 20 and a mass number of 40.
Chlorine has an atomic number of 17 and a mass number of 35.
a Draw diagrams to show the structures of calcium and chlorine
atoms. Make sure you label the calcium and chlorine atoms.
b Draw diagrams to show the ions of calcium and chlorine.
Make sure you label the calcium and chlorine ions.
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2.4 Simple and giant structures
c Explain why the formula for calcium chloride is CaCl2.
You may use diagrams to help you explain.
2.4 Simple and Giant structures
2.4A Ionic or covalent bonds
Focus
This exercise will help you to distinguish between ionic and covalent
substances
Look at the diagrams that show the structures of two substances A and B.
Substance A Substance B
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2 Properties of materials
1 What type of bonding do you think Substance A has? Give a
reason for your answer.
2 Label Substance B to show where there are strong forces.
3 Which substance has bonds where electrons are shared?
4 Which substance has a lattice structure?
5 A substance when dissolved in water conducts electricity.
What type of bonding does it have?
6 Some giant structures are called macromolecules. What type of
bonding do they have?
7 Give an example of a macromolecule.
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2.4 Simple and giant structures
2.4B Properties of ionic and covalent
substances
Practice
In this exercise you will identify properties of substances linked to their structures
Look carefully at the table and answer the questions.
solid, liquid or Ionic or simple
Melting point / Boiling point /
Substance gas at room molecule with
°C °C
temperature? covalent bonds
potassium
770 1500
chloride
Substance X −182 −161
calcium
solid ionic
chloride
ammonia −77 −34
magnesium
2825 3600
oxide
bromine −7 59
simple molecule with
Substance Y 0 100 liquid
covalent bonds
1 Calcium chloride is an ionic compound that is solid at room temperature.
What does that tell you about its melting and boiling points?
2 Is Substance X a solid, liquid or gas at room temperature?
3 List the substances that are solids at room temperature.
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2 Properties of materials
4 List the substances, other than Substance Y, that have simple
molecules with covalent bonds.
5 Suggest what Substance Y is. Give a reason for your suggestion.
6 Which substance, other than Substance Y, is a liquid at
room temperature?
7 Explain why magnesium oxide has high melting and boiling points.
8 Explain why ammonia has low melting and boiling points.
2.4C Giant structures of carbon
Challenge
In this exercise you will link the structure of diamond and graphite to
their properties.
Diamond and graphite are both giant structures formed from the
element carbon.
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2.4 Simple and giant structures
1 Which of the diagrams below represents the structure of diamond
and which graphite?
This structure represents: This structure represents:
2 Graphite is a very soft material. Explain how its structure is related
to its properties.
3 Diamond is the hardest material on Earth. Explain how its
structure is related to its properties.
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