Periodicity

• ATOMIC RADIUS ( Total distance from an atom's nucleus to the outermost orbital of                                      electron )

It gives information about the relative size of an atom.

It decreases across the period ==> nuclear charge increases (more protons) ==> great force of attraction between the positevely-charged nucleus and the outermost electrons ==> small size

It increases as you go down a certain group ==> number of electronic shells increase ==> large atoms

• IONIC RADIUS ( Radius of an atom forming an ion or a ionic bond )

Atoms of Metallic Elements ==> Cations (smaller than their original atoms/Outer shell electrons lost) ==> increasing nuclear charge ==> greater attraction

Atoms of NonMetallic Elements ==> Anions (larger than their original atoms/One or more electrons gained) ==> more repulsion between electrons ==> constant nuclear charge ==> lower force of attraction 

• FIRST IONISATION ENERGY ( Energy needed to remove one electron from an atom )

It increases across the period as the nuclear charge increases.

• ELECTRICAL CONDUCTIVITY ( Measure of a material's ability to accomodate the transport of an electric charge ) 

It increases across the Metals of Period 3 ==> delocalised electrons (free to move) ==> more electrons to make the electric charge flow through them

It decreases across the NonMetals of Period 3 ==> electrons unable to move 

• MELTING POINT ( is the temperature of a solid at which changes its state from solid to liquid at atmospheric pressure )

It depends on the bond and the structure of the element.

Giant molecular structure ==> strong covalent or metallic bonds ==> higher melting point

Simple molecular structure ==> weak Van Der Waals' intermolecular forces ==> lower melting point