Atoms and Ions

• All matter is composed of atoms

• Atoms are made up of protons, neutrons and electrons

• Atoms are most stable when their electron shells are complete A

• toms can lose or gain electrons to achieve this state – they become charged ions

• The chemical properties of an element are determined by the number of electrons in the atom

• Atoms gaining electrons are reduced to negative ions

• Atoms losing electrons are oxidised to positive ions

Bonding

• Covalent bonds

  • electrons are shared between two atoms completing both outer shells

  • a molecule is formed - eg CO₂

 

 

• Ionic bonds

  • electrons are given from one atom to another

  • the resulting + and – charges form an electrostatic bond Eg NaCl

• Hydrogen bonds

  • electrons are not evenly shared

  • one atom becomes slightly –ve and the other slightly +ve forming a weak electrostatic bond.

  • Many of these can have a significant bonding effect. Eg between water molecules