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.

Explain the reason for the relative sizes of the values of the electron affinity for all the elements.

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. Among the other given elements, the halogen chlorine will have the most negative electron affinity value and hence it will have the most favourable electron addition process. Going down group $17$ , the other halogen after chlorine will have lesser negative values gradually, such as bromine and then the iodine. Oxygen belongs to group $16$ and period $2$ of the periodic table and hence will have a lesser negative electron affinity value as compared to the halogens given. Hence, the more favourable electron addition process is:

Chlorine $>$ bromine $>$ iodine $>$ oxygen $>$ neon

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.

Explain the reason for the relative sizes of the values of the electron affinity for all the elements.

Important Questions on Why do Electrons Matter?

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