Atomic Bonding

Atoms of most elements react to form bonds. The atoms either lose, gain or share electrons to form full outer shells like the electronic configurations of noble gases.

Atoms of noble gases do not form bonds because they have a very stable arrangement of electrons in the outer shell. Other electrons react and bond to archieve this.

Ionic bonding

Ionic bond is a bond formed when metals combine with non-metals. When this type of bond is formed, electrons are transferred from the metal atoms to the non-metal atoms during the chemical reaction. In doing this, the atoms become more stable by getting full outer shells.

Always when a metal reacts with a non-metal to form an ionic compound the metal atoms lose electrons and the non-metal atoms gain them. Since the number of electrons lost by the metal is equal to the number of electrons gained by the non-metal, the compound has no overall charge.

Covalent bonding

When two non-metal atoms react together, both need to gain electrons to achieve stable outer shells. They manage this by sharing electrons. Atoms can share only their outer (valence)
electrons. Thats why most of our diagrams only show outer electron only


A molecule is a group of atoms held together by covalent bonds. Since it is made up of molecules, hydrogen is a molecular element. Its formula is H2 which means the molecule is made up of two hydrogen atoms in this case. Elements made up of molecules containing two atoms are called diatomic. Examples of other diatomic elements are; iodine, I2; oxygen, O2; nitrogen, N2; chlorine, Cl2.


a) Carbon dioxide is a compound of carbon and oxygen, two non-metallic elements.
(i) State the name of the type of bonding between a carbon atom and an oxygen atom. …[1]
(ii) Describe, in terms of electrons, the bonding between a carbon atom and an oxygen atom. ….[1]

(b) The compound sodium chloride contains sodium ions and chloride ions.
Describe, in terms of electrons, the formation of ions from the atoms. …[1]



  1. Covalent Bond
  2. The outer shell electrons are shared between carbon and oxygen atoms.

b) sodium loses one electron from the outer shell and becomes a positively charged ion. chlorine gains one electron and become a negatively charged chloride ion.

Comparing ionic and covalent compounds

A metal and a non-metal react together to form an ionic compound.
Ionic compounts exist in form of charged ions held together by strong
electrostatic forces. Non-metals react together to form covalent compounds. Covalent compounts exist as uncharged molecules held together by weak forces of attraction.

Naming the compounds

The following is a guide on naming binary compounds. Binary compounds are compounts which contain only 2 elements.

But some compounds have ‘everyday’ names that give you no clue about
the elements in them. Water (H2O), methane (CH4), and ammonia (NH3) are examples. You just have to remember their formulae! .


Complete the following sentences using words from the list.
Each word may be used once, more than once or not at all.

  • atoms
  • compounds
  • covalent
  • elements
  • ionic
  • ions
  • mixtures
  • molecules
  1. The smallest parts of an element are ……. [1]
  2. All …….. contain atoms joined by sharing pairs of electrons in
    ……… bonds. [2]
  3. Atoms which lose or gain electrons form particles called ……..[1]
  4. Elements in …….. cannot be separated by simple physical processes. Substances in …….can be separated by simple physical processes. [2]


    1. atoms
    2. molecules, covalent
    3. ions
    4. compounds, mixture