Name: Distribution of the Electrons in Shells
Uploaded: 2019-07-19
Duration: 10 min 5 s
Description: We all know that the electrons revolve around the nucleus but do you know how to distribute electrons in different orbits? Let's dive into this video.

Question

The first electron affinity is the energy change when one mole of gaseous atoms gains a mole of electrons. The table below shows the first electron affinity for selected atoms.

The first electron affinity of oxygen is

- 141 kJ \cdot {mol}^{- 1}

.

In terms of electrostatics, oxygen has a lower first electron affinity than chlorine.

Explain why neon has a positive value of electron affinity.

Accepted Answer

The first electron affinity is the energy change when one mole of gaseous atoms gains a mole of electrons, resulting in a mole of gaseous anions (negative ions). It is expressed in units of $kJ \cdot {mol}^{- 1}$ . So the more negative the electron affinity the more favourable the electron addition process is. Not all elements form stable negative ions in which case the electron affinity is zero or even positive. Less energy is required to add an electron from atoms of elements on the left-hand side of the periodic table, which have larger radii and small numbers of valence electrons, compared to adding electrons to elements on the right-hand side. For similar reasons, radii increase down each group of the periodic table and less energy is required to add electrons to atoms of elements with increasing numbers of electron shells. Hence, the electron affinity value increases along a period from left to right. In group $18$ , the valence shell is full, meaning that added electrons are unstable, tending to be ejected very quickly. Going down a group in the modern periodic table, the electron affinity decreases since the electron is being added increasingly further away from the atom. Thus, noble gases like neon have a positive electron affinity value indicating the unstable anion formation. Hence, explained why neon has a positive value of electron affinity.

Important Questions on Why do Electrons Matter?

Learn and Prepare for any exam you want !