1.Atomic size - On moving from left to right in a period the atomic radius decreases.As we move from left to right the atomic number of each succeeding element increases by 1. The addition of extra electron takes place in the same shell. But the addition of extra protons to the nucleus increases the nuclear charge by 1 in each succeeding element.Due to this increased nuclear charge the electrons are attracted closer to the nucleus and hence the atomic radius decreases.
2.Valency - On moving from left to right in a period, the number of valence electrons increases from 1 to 8.Therefore the valency of elements first increases from 1 to 4 and then decreases to 0.
3. Metallic character - On moving from left to right in a period the metallic character decreases while the non- metallic character increases