Periodic trends in atomic properties

    The periodic trends in atomic properties such as ionization energy, electron affinity, and atomic radius can be explained in terms of the concepts of nuclear attraction, electron repulsions, shielding, and penetration.

Ionization energy

    Ionization energy is the energy required to remove an electron from a gaseous atom or ion when the atoms or ion is assumed to be in its ground state. 

Electron affinity

    Electron affinity is the energy change associated with the addition of an electron to a gaseous atom.