Beforeproceeding to explain what is electron affinity, a brief explanation ofthe periodic table and periodic properties is necessary to understand it.
The periodic table is an organized chart of all known elements in which the elements are arranged in rows and columns in increasing order of their atomic numbers.
Theabove arrangement of elements enables us to see a repetition of variousproperties in elements after regular intervals. The properties of elements repeat themselves in the periodic table after regular intervals. These set of repeating properties are known as the Periodic properties.
Electron affinity is a periodic property of elements. Electron affinity is the property of an element which tells us its nature in terms of electronegativity.If the electron affinity of an element is high, then it gains electronseasily, and thus, it is a non metallic element, or, equivalently, an electronegative element. Quantitatively, electron affinity is the amountof energy released when an electron is gained by the neutral atom of an element to form a negatively charged ion.
Electron affinity periodic table
Sinceelectron affinity is a periodic property, it repeats itself in the periodic table after regular intervals, and, consequently, it shows gradual variation in its value as we move across rows and down columns of the periodic table.
The variation of electron affinity depends on two properties of elements
Nuclear charge: As the nuclear charge increases, the electron affinity also increases.
Atomic size: As the atomic size increases, electron affinity decreases and vice versa.
Variation of electron affinity across a row:
Theelements of the same period in the periodic table have the same number of shells, and increasing atomic numbers. Due to this, the atomic size decreases as we move from left to right in a row. As the atomic size decreases slightly, the increase in nuclear charge overrides its effect,and thus the electron affinity of elements increases.
Variation of electron affinity down a group:
Atomicsize increases as we move down a group, and nuclear charge increases. However, the increase in atomic size is greater in effect than the increase nuclear charge, and thus the electron affinity of elements decreases down a group of the periodic table.