Principal: Mr. T. Power, B.A. H.D.E.
Vice Principal: Ms. F. Greene, B.A. H.D.E.

Junior Cert

SCIENCE > BONDING

1. Why Do Elements React?
Elements react so that they can achieve the same electron structure as their nearest noble gas.

2. How Do They React?
There are two ways in which elements chemically react to achieve this:
(a) Ionic Bond
(b) Covalent Bond

3. Valency
The valency is the number of electrons lost, gained or shared in bonding (same as charge on group but no sign).

4. Ion
An ion is what results from the loss or gain of electrons by an atom.

5. Ionic Bond
An ionic bond occurs when there is complete loss or gain of electrons. Example: NaCl.

6. Properties of Ionic Bonds
(a) high melting and boiling points
(b) conduct electricity

7. Covalent Bond
A covalent bond occurs when a pair or pairs of electrons are shared. Example: O₂, N₂, H₂.

8. Properties of Covalent Bonds
(a) low melting and boiling points
(b) don't conduct electricity