Question

Question 1
Use Mendeleev's periodic table to predict the formulae for the oxides of the following elements: K, C, Al, Si, Ba.

Answer 1

Valency of oxygen is 2.
K is in group 1 and has valency 1. Using criss-cross method:

Symbol: K O
$\searrow \swarrow$
Valency: 1 2
Therefore,the oxide formed is: ${\text{K}}_2\text{O}$.

C is in group 14 and has valency 4. Using criss-cross method:

Symbol: C O
$\searrow \swarrow$
Valency: 2 4
Therefore, the oxide will be ${\text{CO}}_2$.

Al is in group 13 and has valency 3. Using criss-cross method:

Symbol: Al O
$\searrow \swarrow$
Valency: 3 2

Therefore, the oxide will be ${\text{Al}}_2{\text{O}}_3$.

Si is in group 14 and has valency 4. Using criss-cross method:
Symbol: Si O
$\searrow \swarrow$
Valency: 4 2
Therefore, the oxide will be ${\text{SiO}}_2$.

Ba is in group 2 and has valency 2. Using criss-cross method:
Symbol: Ba O
$\searrow \swarrow$
Valency: 2 2
Therefore, the oxide will be $\text{BaO}$.