Question

The number of electrons goes on increasing in the outer shell as we move from left to right in a period, why does the atomic size goes on decreasing? 

Answer 1

In a period all elements have same number of shells. As we move from left to right in a period the number of electrons goes on increasing at the same time the number of protons also goes on increasing therefore attraction force of nucleus increases and pulls the valence electrons i.e. the outermost shell towards the nucleus and hence the size of atom goes on decreasing.