Name: Variation of Atomic Radius in Periodic Table
Uploaded: 2019-07-19
Duration: 4 min 6 s
Description: The atomic radius is defined as the distance between the atom's nucleus and the outermost shell. But do you know how it varies in the periodic table? Let's find the answer in this video.

Question

Define ionisation enthalpy and successive ionisation enthalpies. Discuss the factors that influence the magnitude of ionisation enthalpy. What are the general trends of variation of ionisation enthalpy in the periodic table ? Explain.

Accepted Answer

Ionisation enthalpy: It is the minimum energy required to remove an electron from the outermost shell of the isolated gaseous atom.
The ionisation enthalpies required to remove first, second, third, etc. electrons from an isolated gaseous atom are called successive ionisation enthalpies.

The ionisation enthalpy of an atom depends upon various factors:
(i) Electronic configuration: Elements having half -filled or fully-filled outermost subshells have higher ionisation enthalpy values than expected values due to extra stability associated with these orbitals.
(ii) Atomic Size: The bigger the size of atom, the less tightly the outermost electrons are bound to the nucleus. Hence, the ionisation enthalpy is lower.
(iii) Penetration power of electrons: Ionisation enthalpy increases as the penetration effect of the electrons increases. Thus, within the same shell, the penetration power decreases in the following order: $s > p > d > f$ .

(iv) Nuclear charge. The ionisation enthalpy increases with increase in nuclear charge. This is due to the fact that with increase in nuclear charge, the electrons of the outer shell are more firmly held by the nucleus and thus greater energy is required to pull out an electron from the atom.

In general, the ionisation enthalpy decreases down the group. On moving down a group, the size of the elements increases drastically due to the addition of the new shell, hence, the interaction between nucleus and the outermost electrons decreases, thus the ionisation enthalpy decreases.

In general, the ionisation enthalpy increases along the period. As we move across a period from left to right, the nuclear charge increases and the atomic radius decreases though the principal quantum number of the valence shell remains the same. As a result of increased nuclear charge and simultaneous decrease in atomic radius, the valence electrons are more and more tightly held by the nucleus as we move from left to right in a period. Consequently, more and more energy is needed to remove the electron and hence ionisation enthalpies keep on increasing.

Define ionisation enthalpy and successive ionisation enthalpies. Discuss the factors that influence the magnitude of ionisation enthalpy. What are the general trends of variation of ionisation enthalpy in the periodic table ? Explain.

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