Chemistry Tuition Center Singapore – Ionisation Energy

Question

Explain why the 1^st ionisation energy generally increases across Period 3.

Answer

Across the Period, nuclear charge increases due to increase in number of protons. Shielding effect is similar as the valence electrons are in the same quantum shell.

Hence, valence electrons are more strongly attracted to the nucleus and therefore more energy is required to remove an electron.

Note

• As I.E. involves only the removal of valence electron, ‘valence’ must be mentioned when referring to the electron being removed.

  This explanation can be used to explain the difference in 1st I.E. of elements within the SAME period dexcluding the d-block elements), where the I.E. of the element with the higher proton number is larger. (Eg. to explain why the 1st I.E. of Cl is larger than that of S)

Please contact Mr Ong @ 9863 9633 if you have any question regarding Atomic Structure