Valence bond theory was proposed by .

A chemical compound has the following Lewis notation:

How many valence electrons does element $\mathrm{Y}$ have?

$\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$ are three elements with atomic number $6, 11$ and $17$ respectively.

Which of these can form ionic as well as covalent bonds? 

Draw a simple diagram to show how electrons are arranged in the following covalent molecule.

Water $\left({\mathrm{H}}_2\mathrm{O}\right)$