Name: Nomenclature of Elements With Atomic Numbers > 100
Uploaded: 2019-07-19
Duration: 16 min 52 s
Description: Elements with atomic number greater than 100 have been named after famous scientists, although the universally accepted names are the names derived from IUPA...

Question

What are electron affinity and ionisation energy? Explain.

Arrange nitrogen, oxygen and fluorine in the increasing order of their ionisation energy giving reasons.

Accepted Answer

When an electron is added to a neutral gaseous atom to convert it into a negative ion, the enthalpy change accompanying the process is defined as the Electron affinity or electron gain enthalpy. Electron gain enthalpy becomes more negative with increase in the atomic number across a period. The effective nuclear charge increases from left to right across a period and consequently it will be easier to add an electron to a smaller atom since the added electron on an average would be closer to the positively charged nucleus while down the group electron affinity decreases as atomic size increases.

A quantitative measure of the tendency of an element to lose electron is given by its Ionization Enthalpy. It represents the energy required to remove an electron from an isolated gaseous atom in its ground state. Across a period, increasing nuclear charge outweighs the shielding. Consequently, the outermost electrons are held more and more tightly and the ionization enthalpy increases across a period. As we go down a group, the outermost electron being increasingly farther from the nucleus, there is an increased shielding of the nuclear charge by the electrons in the inner levels. In this case, increase in shielding outweighs the increasing nuclear charge and the removal of the valence electron requires less energy down a group.

Increasing order of ionisation energy: Oxygen < fluorine < Nitrogen

Electronic configuration of nitrogen and oxygen is:

Nitrogen- $1 s^{2} 2 s^{2} 2 p^{3}$

Oxygen- $1 s^{2} 2 s^{2} 2 p^{4}$

Fluorine- $1 s^{2} 2 s^{2} 2 p^{5}$

An atom is highly stable when its valence orbital is completely filled or half-filled and Nitrogen is known to have a half-filled $p$ -orbital and is quite stable. So, $p$ -orbital in nitrogen is more stable than in oxygen. Therefore, the amount of energy required to remove an electron from the valence shell of nitrogen will be much higher than the energy required to remove an electron from the valence shell of oxygen. So, the ionization energy of nitrogen is more than that of oxygen. In oxygen, two of the four 2p electrons occupy the same atomic orbital and this results in increased electron-electron repulsion in the oxygen atom. Hence, oxygen will have lower ionization enthalpy than the fluorine atom.

What are electron affinity and ionisation energy? Explain.

Arrange nitrogen, oxygen and fluorine in the increasing order of their ionisation energy giving reasons.

Important Questions on Classification of Elements and Periodicity in Properties

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