Electron affinity periodic table, units and factors

Hi friends welcome to my website today, I am going to tell you about the Electron affinity periodic table.

Electron affinity definition

        The electron affinity is the least amount of energy released or absorbed when we added an electron to the outermost shell of an individual gaseous atom. It is represented by ‘E’. The neutral atom is converted into an anion after accepting the electron.

Electron affinity exceptions

          When the first electron is added to the individual gaseous atom then energy is released but when 2^nd electron is added into the uni-negative ion then energy is absorbed. It becomes more difficult to add a 2^nd electron in uni-negative ion because electrons also have a negative charge and already negatively charged ions repel incoming electrons.  This process is known as the endothermic process. 2nd electron affinity has a positive value. The reaction in which energy is released is known as the exothermic process. This type of behavior is shown by very few elements (non-metals and lighter elements).

          It is very difficult to measure electron affinity as compared to ionization energy. It can be measured by the Born-Haber cycle.

Units

          The units for units of electron affinity are:

Ø Electron volts per atom

Ø Kj/ mole

First electron affinity E₁

          The energy released to add the first electron in the outermost shell of the individual gaseous atom and converted it into a uni-negative ion is known as First electron affinity E₁. The release of energy in a reaction is known as the exothermic process.

Electron affinity periodic table

2^nd electron affinity

                The energy absorbed to add the 2nd electron in the outermost shell of a singly negative ion and converted it into doubly negative ion is known as second ionization energy E₂. The value of 2^nd electron affinity is positive for those elements which have one or two valences and their shell are close to the nucleus. The absorption of energy in a reaction is known as the endothermic process.

Electron affinity periodic table

Factors of electron affinity

          Electron affinity depends upon different factors:

Ø Atomic radius

Ø Nuclear charge

Ø Shielding effect/screening effect

Trends in electron affinity

          Electron affinity has a different trend in periods and groups.

Trend in groups

          The electron affinity of elements decreases in groups from top to bottom with the addition of each new shell in each new period. 

Reason

          Electron affinity decreases in a group because in each new period new shell is added to an element, so it becomes very easy to add electrons from an outermost shell. So for the addition of electrons very little energy is required.

Trend in periods

          Electron affinity increase in a period from left to right with the increase of nuclear charge in each new group.

Reason

          Electron affinity increases from left to right in a period because in each new element nuclear charge increases. Due to the increase of nuclear charge, the nucleus tightly bound the outermost shell electrons, as a result, the atomic radius of elements decreases and it becomes very difficult to add electrons in the outermost shell. So for the addition of electrons requires very high energy.