Chemical Bonding Notes
Oxford AQA IGCSE Chemistry: Revision notes
Key facts
- A compound has two or more elements chemically combined.
- Atoms bond to get a full outer shell.
- Ionic: electrons transferred, metal + non-metal.
- Covalent: electrons shared, non-metal + non-metal.
- Metallic: delocalised electrons in a lattice of positive ions.
Why atoms bond
Atoms transfer or share electrons to reach the stable arrangement of a noble gas.
A compound has atoms of two or more elements chemically combined. Most atoms do not have a full outer shell, which is unstable. By transferring or sharing outer electrons they achieve the electron arrangement of a noble gas.
Neon
2,8
Argon
2,8,8
- Full outer shellstable, like a noble gas
Why do atoms form bonds?
Ionic bonding
In ionic bonding, a metal atom transfers electrons to a non-metal atom, forming oppositely charged ions that attract.
The metal atom loses electrons to form a positive ion; the non-metal gains them to form a negative ion. Both ions have a noble gas arrangement.
Ionic bonding is the strong electrostatic attraction between the oppositely charged ions.
Sodium atom
2,8,1
Sodium ion
2,8
Chlorine atom
2,8,7
Chloride ion
2,8,8
- 1
Metal loses electrons
Forms a positive ion
- 2
Non-metal gains electrons
Forms a negative ion
- 3
Attraction
Holds the ions together
In ionic bonding, electrons are...
Covalent bonding
In covalent bonding, atoms share pairs of electrons so each reaches a noble gas arrangement.
Covalent bonding happens usually between non-metal atoms. Each atom contributes one electron to a shared pair, and the pair counts towards the outer shell of both. It forms simple molecules or giant covalent structures.
- 1
Two non-metal atoms approach
each has an incomplete outer shell
- 2
Each contributes one electron
to a shared pair
- 3
The pair counts for both atoms
each reaches a noble gas arrangement
- Covalent bondshared pair of electrons
Covalent bonds usually form between...
Metallic bonding
In metals, the outer electrons are delocalised and hold a lattice of positive ions together.
Metal atoms form a giant regular lattice of positive ions. The outer electrons become delocalised: free to move throughout the structure.
Strong electrostatic attraction between the positive ions and the delocalised electrons holds the metal together.
Metal lattice and delocalised electrons
- Metallic bondpositive ions + delocalised electrons
What is delocalised in a metal?
Telling them apart
Check whether the substance has a metal, a non-metal or only metal atoms.
Metal and non-metal means ionic; two non-metals means covalent; only metal atoms means metallic.
- 1
Metal and non-metal
ionic: electrons transferred
- 2
Two non-metals
covalent: electrons shared
- 3
Only metal atoms
metallic: electrons delocalised
| Ionic | Covalent | Metallic | |
|---|---|---|---|
| Electrons | Electrons transferred | Electrons shared | Electrons delocalised |
| Elements | Metal + non-metal | Non-metal + non-metal | Metal atoms only |
Ionic
- Electrons:
- Electrons transferred
- Elements:
- Metal + non-metal
Covalent
- Electrons:
- Electrons shared
- Elements:
- Non-metal + non-metal
Metallic
- Electrons:
- Electrons delocalised
- Elements:
- Metal atoms only
Magnesium chloride (metal + non-metal) is...
Try an exam question
Describe how sodium and chlorine atoms form an ionic bond.
[4 marks]
- [1]Sodium loses an electron to form a positive ion.
- [1]Chlorine gains the electron to form a negative ion.
- [1]Both ions have a noble gas electron arrangement.
- [1]The ions attract by strong electrostatic forces.
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