The document discusses ionic bonding and how ions are formed. It defines key terms like atoms, ions, and molecules. Atoms form ions by gaining or losing electrons to achieve a full outer shell configuration. Ions have partial positive or negative charges. When oppositely charged ions interact, they form ionic compounds held together by electrostatic attraction. Ionic compounds have properties like high melting points, brittleness, and the ability to conduct electricity when molten or dissolved due to mobile ions.

1. C3b How atoms combine - Ionic Bonding
Revision (you MUST know these definitions)
• An atom is the smallest particle that exists on its own. It is neutral (no charge).
e.g.
• A molecule is made from 2 or more atoms chemically joined
e.g.
New definitions to learn:
• An ion is a ____________ atom or group of atoms
e.g. a magnesium ion,
a carbonate ion,
• Ions can be _______________ charged (+) or _________________ charged (-)
• For your exam you must be able to recognise an ion, an atom and a molecule
from given formulae.
Formulae Atom, Molecule or Ion?
Cu
Cu2+
CuSO4
Al3+
O2-
N
Cl2
Why are ions formed?
Atoms are “happiest” (most _______ ) when they have a full outer shell of electrons.
They __________ to complete their shells. Metals transfer electrons to non-metals.

2. How are Ions formed?
• Remember that electrons are ________________ charges (e-)
• So, positive ions are formed by the __________ of electrons from atoms
e.g:
• Negative ions form by atoms ________________ electrons
e.g.
• When a metal and a non-metal ________________ electrons in this way to form
positive and negative ions, the opposite charges ______________ and an
____________________________ forms between the metal and the non-metal.
“dot and cross” models
We use these diagrams to show the ionic bonding in ionic compounds. You need to
know 4 dot and cross models really well:
sodium chloride
magnesium oxide
sodium oxide
magnesium chloride

3. Deducing the formula of an ionic compound
• If we know the ions that a compound is made from, we can work out the chemical
_________________ of that compound.
• Compounds have no overall charge so the + and – charges must ______________
e.g. What is the formula for aluminium chloride?
An aluminium ion = Al3+ you need three negative charges
to cancel out the three positive
A chloride ion = Cl- charges
So, aluminium chloride =
Task
In the table below is a list of some ions. Use them to work out the formulae of the
compounds under the table (the last few are quite difficult but you need to be able to
complete the first 7 at least).
Positive ions Negative Ions
Na+ Cl-
Ca2+ I-
Al3+ O2-
Fe2+ OH- (hydroxide ion)
Fe3+ SO4 2-
(sulphate ion)
1. Sodium chloride = NaCl 6. Iron (III) chloride*
2. Calcium chloride 7. Iron (II) chloride*
3. Aluminium iodide 8. Sodium hydroxide
4. Calcium oxide 9. Sodium sulphate
5. Sodium oxide 10. Iron (III) sulphate*
*Note: II is the roman numeral for 2 III is the roman numeral for 3

4. What Properties do Ionic Compounds have?
• Ionic compounds are always made from a _____________ and a _____________
e.g.
• Due to the strong electrostatic forces of attraction between the positive (+) and
negative (-) ions, ionic compounds:
1.
2.
3.
4.
5. conduct electricity when ________________ or in _________________
because the ions are ________________________________.
Exam question: Explain why solid sodium chloride, NaCl does not conduct
electricity but a when it is molten or in solution (dissolved in water) it will conduct.
Answer:
1.
2.