What is covalent bond and how it is formed?

The elements $\mathrm{w}, \mathrm{x}, \mathrm{y}$ and $\mathrm{z}$ have atomic number $7, 9, 10$ and $11$ respectively. Write the formula of the molecules that would be formed between the following pair. Indicate the type of bond present using dots and crosses to represent the valence electrons. 
$\mathrm{w}$ and $\mathrm{x}$

The elements $\mathrm{w}, \mathrm{x}, \mathrm{y}$ and $\mathrm{z}$ have the atomic number $7, 9, 10$ and $11$ respectively. Write the formula of the molecules that would be formed between the following pair. Indicate the type of bond present using dots and crosses to represent the valence electrons.
$\mathrm{x}$ and $\mathrm{x}$