Ionic and Covalent Bonding

Group 8 or 0 of the periodic table contain a group of atoms called noble gases; Helium, Neon, Argon, Krypton, Xenon and Radon.

They all have a full outer shell of 8 electrons, which make them very stable and unreactive.

All the other atoms in the periodic table want to be just like the noble gases and do so by bonding with other atoms to form a complete outer shell.

Atoms can do this by either transferring their electrons to another atom forming an ionic bond, or by sharing to form a covalent bond.

Ionic bonding

• Usually occurs between a metal and a non-metal. 
• When metals react they usually lose electrons. As they now have fewer electrons than protons they form positive ions.
• When non-metals react they usually gain electrons. As they now have more electrons than protons they form negative ions.
• So when a metal atom bonds with a non-metal atom, the metal donates its electrons to the non-metal to form a positive metal ion and a negative non-metal ion.
• The ions are attracted to each other by an ionic bond.

Below is a dot and cross diagram to show what happens when a sodium atom bonds with a chlorine atom:

 The sodium ion that forms has a +1 charge and the chloride ion has a -1 charge. The formula of the compound formed is NaCl. 


Covalent bonding

• Usually occurs between two non-metals.
• As explained before, non-metals usually gain electrons but as they both can’t gain electrons they share their electrons between them. This is known as a covalent bond, with a zero overall charge.

Below is a dot and cross diagram showing what happens when two chlorine atoms bond together to form a chlorine molecule (again only the outer shell electrons are shown):

Each chlorine atom has 7 electrons in their outer shell so when they come together a single covalent bond is formed from one shared pair of electrons. The formula of the chlorine molecule that forms is Cl₂.

When two oxygen atoms come together, it is slightly different because they each have 3 pairs of electrons in their outer shell, so when the two atoms attract a double covalent bond is formed consisting of two pairs of electrons.