Question

In group 17, which property does not follow the regular trend?

• A. Electron affinity
• B. Ionisation energy
• C. Covalent radii
• D. Ionic radii

Hint:

Keep in mind that certain properties such as electron affinity can show irregular trends due to specific atomic characteristics like size and electron-electron repulsion.

Answer 1

The Correct Option is A

In group 17 of the periodic table (the halogens), the properties generally follow a regular trend as you move down the group. However, one property does not follow this trend:

1. Electron Affinity: Electron affinity typically increases across a period (left to right), but in group 17, the electron affinity does not increase regularly down the group. Fluorine, for example, has a lower electron affinity than chlorine, which is an anomaly due to the smaller size of the fluorine atom, which results in repulsion between the added electron and the lone pairs of electrons in the valence shell.
2. Ionisation Energy: Ionisation energy generally decreases as you go down a group, but the trend is fairly regular.
3. Covalent Radii: The covalent radii increase as you go down group 17 in a regular fashion, as larger atoms with more electron shells form covalent bonds.
4. Ionic Radii: The ionic radii also follow a regular trend as you go down group 17, increasing with the number of electron shells. Thus, the correct answer is electron affinity, as it does not follow the regular trend in group 17.