Fri March 28, 2014 By: Sayoni Maiti

Are ionisation enthalpy and electron affinity the same thing?

Expert Reply
Fri March 28, 2014
No. Ionisation enthalpy and electron affinity are two periodic properties.
Ionisation enthalpy :
It is the energy required to remove an electron from a neutral isolated gaseous atom and convert it into a positively charged gaseous ion is called ionisation energy.
M(g)   + I.E  →  M+(g)   + e-
Trends in Ionisation energy
Across a period
Ionisation energy tends to increase as one moves from left to right across a period because atomic size decreases due to an increase in the nuclear charge and thus more energy is required to remove the electron.
Down a group
Ionisation energy decreases with an increase in the atomic size i.e. it decreases as one moves down the group.
Electron affinity:
The amount of energy released while converting a neutral gaseous  atom into a negatively charged ion by the addition of electron is called electron affinity.
X(g)  + e-    →  X-(g)   + E.A
Trends in Electron affinity
In a period from left to right in a horizontal row of the periodic table, the atomic size decreases and the nuclear charge increases, so the electron affinity increases.
Down a group
Moving from the top to the botton in a group, the atomic size increases more than the nuclear charge, thereby causing a net decrease in E.A.
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