Question

The first ionization energies of four consecutive elements in the periodic table are :
Sodium =

494 {KJmol}^{- 1}

Magnesium=

736 {KJmol}^{- 1}

Aluminium =

577 {KJmol}^{- 1}

Silicon=

786 {KJmol}^{- 1}

Explain the general increase in ionisation energy from sodium to Silicon.

Accepted Answer

The general increase is seen in first ionization energy from sodium to silicon, In the whole of $3^{rd}$ period, the outer electrons are in 3-level orbitals. These are all the same sort of distances from the nucleus, and are screened by the same electrons in the first and second levels. The major difference is the increasing number of protons in the nucleus as you go from sodium across to argon. That causes greater attraction between the nucleus and the electrons and so increases the ionisation energies. In fact, the increasing nuclear charge also drags the outer electrons closer to the nucleus. That increases ionisation energies still more as you go across the period.
In the case of aluminium, there is a decrease in energy, It happened because of the extra p-orbital present in its electronic configuration.i.e; ${}_{13}{Al} = 1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{1}$ .

Lawrie Ryan and Roger Norris Solutions for Chapter: Electrons in Atoms, Exercise 13: Questions

Lawrie Ryan Chemistry Solutions for Exercise - Lawrie Ryan and Roger Norris Solutions for Chapter: Electrons in Atoms, Exercise 13: Questions

Questions from Lawrie Ryan and Roger Norris Solutions for Chapter: Electrons in Atoms, Exercise 13: Questions with Hints & Solutions

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