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Classification of Elements and Periodicity in Properties

Short Answer Type

101. Define atomic size or atomic radius of an element. Why is it not possible to determine its absolute value?

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Long Answer Type

102.

What do you mean by covalent radius?

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103.

How do atomic radius vary in a period and in a group? How do you explain the variation?

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Short Answer Type

104.

Why do the noble gas elements have exceptionally high atomic radii?
Or
In a period, generally the size of the atom decreases with rise in atomic number, but at the end of each period, atomic size of the noble gas increases abruptly. Why is it so?

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Long Answer Type

105. Define vander Waal’s radius and compare it with covalent radius.

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Short Answer Type

106.

Atomic radii of noble gases are essentially the vander Waal's radii. Comment.

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107.

What is ionic radius?

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108.
Why is the radius of cation less than that of parent atom?

A cation is formed by the loss of one or more electrons from the neutral gaseous atom. With the removal of one or more electrons from an atom, a magnitude of nuclear charge remains the same as that of the parent atom while the number of electron decreases. As a result, the same nuclear charge acts on the lesser number of electrons. In other words, the effective nuclear charge per electron increases and therefore, electrons are more strongly attracted and pulled towards the nucleus. This causes the decrease in the size of positive ion.

For example.

Atomic radius of Na = 154 pm (Nuclear charge = + 11 ; e = 11)
Ionic radius of Na⁺⁺ = 95 pm (Nuclear charge = + 11 ; e = 10)

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