What is 1st ionization energy?
The first ionization energy is the energy required to take away the first electron from a neutral atom.
The first ionization energy generally increases as the atomic number increases across a period, with a few exceptions. In the second period the I A ionization is less than the II A. But the II A is more than the III A because of the stability of the filled S subshell.
Then the III A is less than the IV A which is less than the V A but the V A is more than the VI A because of the stability of the half filled p subshell. The The VIA is less than the VIIA which is less than the VIIIA VIIII is a completely filled second energy level and is very stable so removing an electron requires a great deal of energy.
The first ionization energy generally decreases as the atomic number increases within a family. The greater the distance from the nucleus the electron is the easier it is to remove the electron, and the lower the first ionization energy.