Forming bonds (AQA GCSE Chemistry Combined Science): Revision Notes
Forming bonds
Most atoms are not stable on their own and need to form chemical bonds with other atoms. Noble gases are different - they don't usually react because they already have full outer electron shells. All other elements form chemical bonds to become more stable.
Understanding why atoms form bonds is fundamental to chemistry. Atoms are essentially "seeking" stability, and this stability comes from having complete outer electron shells, just like the noble gases naturally possess.
There are three main types of strong chemical bonds that atoms can form.
Ionic bonds
Ionic bonds happen when metals and non-metals react together. This type of bonding works through electron transfer.
Here's how ionic bonds form:
- Metal atoms give away their outer electrons completely
- Non-metal atoms take these electrons
- This creates charged particles called ions
- Metal atoms become positive ions (they lost electrons)
- Non-metal atoms become negative ions (they gained electrons)
- The positive and negative ions attract each other strongly
Worked Example: Sodium Chloride Formation
When sodium reacts with chlorine:
- Sodium atom (Na) loses one electron → becomes Na⁺ ion
- Chlorine atom (Cl) gains that electron → becomes Cl⁻ ion
- The opposite charges attract: Na⁺ + Cl⁻ → NaCl (sodium chloride)
Chemical equation:
Both types of ions end up with full outer electron shells, which makes them stable. The attraction between oppositely charged ions creates very strong bonds.
The key to ionic bonding is complete electron transfer - electrons are completely given from one atom to another, creating charged ions that attract each other.
Covalent bonds
Covalent bonds form when non-metal atoms join together. Instead of giving away electrons, the atoms share them.
This is how covalent bonding works:
- Two or more non-metal atoms come close together
- They share pairs of electrons between them
- Each shared pair creates one covalent bond
- Sharing electrons helps both atoms get full outer shells
- The shared electrons hold the atoms together strongly
You'll find covalent bonds in molecules made from non-metal elements. For example, chlorine gas () has two chlorine atoms sharing electrons, and water () has hydrogen and oxygen atoms sharing electrons.
In covalent bonding, think of it as atoms "holding hands" by sharing electrons, rather than one atom completely taking electrons from another as in ionic bonding.
The bond between atoms that share electrons is very strong, which is why many covalent compounds are hard to break apart.
Metallic bonds
Metallic bonds only happen in metals and metal mixtures (called alloys). This type of bonding is quite different from the other two.
Here's what happens in metallic bonding:
- Metal atoms lose their outer electrons to become positive ions
- These electrons don't stay with any particular atom
- Instead, they move freely throughout the whole structure
- The metal ions arrange themselves in a regular 3D pattern called a lattice
- The moving electrons create a "sea of electrons" around the positive ions
This sea of moving electrons creates strong attractions between the metal ions and the electrons. This is what holds metals together and gives them their special properties like being able to conduct electricity.
The "sea of electrons" model explains why metals can conduct electricity (electrons can move freely) and why they're malleable (the electron sea can flow around moving ions without breaking bonds).
Naming simple compounds
When two different elements join together, the compound name tells you what's inside:
- The first part comes from the metal or first element
- The second part comes from the non-metal, but ends in "-ide"
Worked Examples: Compound Naming
- Hydrogen + sulphur = hydrogen sulphide ()
- Potassium + nitrogen + oxygen = potassium nitrate ()
- Sodium + chlorine = sodium chloride ()
- Magnesium + oxygen = magnesium oxide ()
Key Points to Remember:
- Noble gases don't usually bond because they already have full outer shells
- Ionic bonds form between metals and non-metals through electron transfer
- Covalent bonds form between non-metals by sharing electrons
- Metallic bonds happen in metals with electrons moving freely
- All three types of bonds are strong and help atoms achieve stable electron arrangements
- Compound names ending in "-ide" contain just two different elements