What are the trends left to right across a period?

Explanation:

Trend along period:

As we move from left to right across the periodic table the number of valance electrons in an atom increase.The atomic size tend to decrease in same period of periodic table because the electrons are added with in the same shell. When the electron are added, at the same time protons are also added in the nucleus. The positive charge is going to increase and this charge is greater in effect than the charge of electrons. This effect lead to the greater nuclear attraction. The electrons are pull towards the nucleus and valance shell get closer to the nucleus. As a result of this greater nuclear attraction atomic radius decreases. Because of this ionization energy also increases. Electron affinity also increases from left to right with increase of atomic number.

The melting and boiling points increases as  number of valance electrons increases but this pattern is followed up to the group IVA then it is decreased upto the group eighteen.