Question

How does the number of valence electrons change from left to right across the periodic table?

Answer 1

While going from left to right across a period each time a new electron is added to the successive element.

Example:

ELEMENT:                           Na     Mg      Al       Si      P      S     Cl     Ar

VAlENCE ELECTRONS:       1         2        3        4       5       6    7       8

VALENCY:                             1         2         3       4       3        2     1      -

HOPE THIS HELPS U..