Periodic Table

Atomic Size
The distance between the centre of the nucleus and the outermost shell of an atom is it's atomic radius. The Atomic radius determines the Atomic Size, since an atom is radially symmetric.

Nuclear Charge
the amount of Electrostatic Force of Attraction exerted by the Nucleus on the outermost shell is called Nuclear Charge.

Shielding Effect
Due to presence of innermost electrons, the nuclear charge on the outermost shell is suppressed. This is called Shielding Effect.

Effective Nuclear Charge = Z - σ

where σ is the shielding constant.

Inert Pair Effect
The presence of intervening d & f electrons produce poor shielding effect in heavier atoms. This poor shielding effect gives rise to higher nuclear charge and smaller atomic size.

Ionisation Enthalpy
The amount of energy absorbed during ionization of an atom is called ionization enthalpy.

Electron Gain Enthalpy
The amount of energy released while gaining an electron is called Electron Gain Enthalpy.

Electronegativity
The stability of elements and compounds is decided by its electron charge density.

The electron charge density is calculated by considering the no. of electrons and Atomic Size. Charge density is directly proportional to no. of electrons and it is inversely proportional to the atomic size.

While considering elements of the same period, we consider their electronegativity values and not their atomic sizes to determine their stability. e,g. C, O , N.

Elements having higher electronegativity values are more stable, since they have the ability to carry the negative charge.