Question

What does electron affinity measure?

Answer 1

In order to begin with, one must know that electron affinity is the potential energy change of the atom when an electron is added to a neutral gaseous atom to form a negative ion. So the more negative the electron affinity the more favourable will be the electron addition process. Not all elements form stable negative ions in such case the electron affinity can be zero or even positive.

Complete answer:
The amount of energy released when an electron is applied to a neutral atom to form an anion is known as electron affinity. When an electron is added to a neutral atom in the gaseous state, the amount of energy released is called electron affinity. To put it another way, when an electron is applied to a neutral atom, energy is emitted, but the sum depends on a number of factors.

The atomic radius and the effective nuclear charge are the two most important factors. The greater the pull from the protons in the nucleus, the smaller the radius, the simpler it will be for the electron to add on. When an electron is added, it will be at this distance from the nucleus. X + e X + energy is the formula for this.

Periodic Trends in Electron Affinity: Electron affinity is the amount of energy released when an electron is applied to a neutral atom to form an anion. The measurement of electron affinities is difficult.Over time, electron affinity increases from left to right. The overall pattern arises as a result of increased nuclear attraction over time.

As the group progresses, the electron affinity can decrease as the electron is added further away from the atom. Less strongly bound, and thus closer to a free electron in energy.
Electron affinity= $\dfrac{1}{\text{atomic size}}$
When we shift from left to right over time, the atomic size decreases due to an increase in the nuclear force, and hence the electron gain enthalpy rises. Moving down a group in the periodic table causes the atomic size to increase, allowing the value of electron gain enthalpy to decrease.

The first electron affinity of a given element is always negative, while the second electron affinity is always positive, or endothermic. Since the second electron must be pushed into the mono negative ion, this is the case. The electron affinity is derived indirectly from the Born-Haber cycle and cannot be calculated directly.

Note: One must take note that since the electrons added to the energy levels get closer to the nucleus, the nucleus and its electrons become more attractive. Electron affinity increases upward through periods of a periodic table for the groups and from left to right.