0.4 Chemical bonding

Another way of representing molecules is using Couper notation . In this case, only the electrons that are involved in the bond between the atoms are shown. A line is used for each covalent bond. Using Couper notation, a molecule of water and a molecule of $\mathrm{HCN}$ would be represented as shown in figures [link] and [link] below.

Atomic bonding and lewis notation

1. Represent each of the following atoms using Lewis notation:
   1. beryllium
   2. calcium
   3. lithium
2. Represent each of the following molecules using Lewis notation:
   1. bromine gas ( $\mathrm{Br}{}_2$ )
   2. carbon dioxide ( $\mathrm{CO}{}_2$ )
3. Which of the two molecules listed above contains a double bond?
   
4. Two chemical reactions are described below.
   • nitrogen and hydrogen react to form $\mathrm{NH}{}_3$
   • carbon and hydrogen bond to form a molecule of $\mathrm{CH}{}_4$
   For each reaction, give:
   1. the valency of each of the atoms involved in the reaction
   2. the Lewis structure of the product that is formed
   3. the chemical formula of the product
   4. the name of the product
5. A chemical compound has the following Lewis notation:

   

   1. How many valence electrons does element $\mathrm{Y}$ have?
   2. What is the valency of element $\mathrm{Y}$ ?
   3. What is the valency of element $\mathrm{X}$ ?
   4. How many covalent bonds are in the molecule?
   5. Suggest a name for the elements $\mathrm{X}$ and $\mathrm{Y}$ .

Ionic bonding

The nature of the ionic bond

You will remember that when atoms bond, electrons are either shared or they are transferred between the atoms that are bonding. In covalent bonding, electrons are shared between the atoms. There is another type of bonding, where electrons are transferred from one atom to another. This is called ionic bonding .