Describe and explain the trend in first ionisation energy down group 2 of the periodic table.

Firstly, we must consider the definition of first ionisation energy (1st IE). Thermodynamically, it is the enthalpy change when one mole of electrons is removed from a mole of gaseous atoms of a particular element to form a mole of singly charged gaseous ions:

A (g) → A+ (g) + e-

Next, we must think about what changes physically as we move down a group in the periodic table and how this will affect this enthalpy change. We know that moving one step down a group means the addition of a number of protons to the nucleus, increasing nuclear charge. However, we also know it involves the addition of an extra complete shell of electrons between the nucleus and the outer electron, increasing atomic radius. This shell will have a shielding effect on the electrostatic attraction between the outer electron and the nucleus, outweighing the attraction due to the additional protons. Therefore, the attraction between nucleus and outer electron is weaker moving down the group, so less energy is required to remove it, resulting in a lowering in 1st IE. This means a negative trend is expected.

Answered by Thomas F. Chemistry tutor

8287 Views

See similar Chemistry A Level tutors

Related Chemistry A Level answers

All answers ▸

Explain Le Chatelier's Principle


Deduce which of Na+ and Mg2+ is the smaller ion. Explain your answer.


What are electrophilic addition reactions of alkenes?


A solution of acetic acid and sodium acetate was prepared, by dissolving 4.1 g of sodium acetate in 750 cm^3 of 0.085 mol/dm^3 acetic acid, at 25 degrees. 10 Cm^3 of 2 mol/dm^3 HCl was added. Ka is 1.76*10^-5, calculate and explain the change in pH


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo
Cookie Preferences