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Classification of Elements and Periodicity in Properties

Long Answer Type

161.

A, B, C are three elements, B is an inert gas element other than helium; with this information, complete the table given below:

Element	Atomic No.	No. of electrons in the valence shell	Group to which element belongs
A	Z - 1
B	Z
C	Z+1

Also, explain the following:
(i) Electron gain enthalpy of element A has large negative value than that of C.

(ii) Ionisation enthalpy of element C is less than that of A.

(iii) Electron gain enthalpy of B is positive.

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162.

Define electronegativity. Explain the factors influencing electronegativity. How does it vary along periods and groups? what are its units?

238 Views

163.

What is the importance of electronegativity?

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Short Answer Type

164.

Explain giving various reasons for the variation of electronegativity along a period and along a group.

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Long Answer Type

165.

What is the basic difference between the terms electronegativity and electron gain enthalpy?

149 Views

Short Answer Type

166.

How would you react to the statement that the electronegativity of N on Pauling scale is 3.0 in all the nitrogen compounds?

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Long Answer Type

167.

Give a brief account of valence ?

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168.
The valence of representative elements is either equal to the number of valence electrons or eight minus the number. What is the basis of their rule?

The electrons present in the valence shell (outermost shell) are called valence electrons and their number determines the valency of the element. It has been found that in the case of representative elements (s-and p-block elements), the valency of an element is either equal to the number of valence electrons or eight minus the number of valence electrons, e.g. consider the hydrides of 2nd period i.e. groups 1,2, 13, 14, 15, 16, 17.

Group	1	2	13	14	15	16	17
Compounds	LiH	BeH₂	BH₃	CH₄	NH₃	H₂O	HF
No. of valence electrons	1	2	3	4	5	6	7
Valency of element	1	2	3	4	8-5 =3	8-6 =2	8-7 =1

From the above table, it is clear that valency of the representative elements of groups 1, 2, 13 and 14 is equal to the number of valence electrons. But the valency of representative elements of group 15, 16 and 17 is equal to eight minus number of valence electrons.

The valency of any element is the number of electrons which it loses, joins or shares with other atoms to attain the nearest inert gas configuration. The elements of groups 1, 2 and 13 lose 1, 2 and 3 electrons respectively to attain the nearest noble gas configuration. Thus, the valency of the elements of groups 1, 2 and 13 is equal to the number of their valence electrons. The elements of group 14 have four electrons in their respective valence shells and thus attain noble gas configuration only by sharing with four more electrons of other atoms. Therefore, the valency of elements of group 14 is also equal to the number of their valence electrons.

The elements of group 15, 16 and 17 have 5, 6 and 7 electrons in their respective valence shells and hence they acquire 3 (8-5), 2 (8-6) and 1 (8-7) electrons either by gaining or sharing electrons from other atoms to attain the nearest inert gas configuration. Thus, the valency of the elements of groups 15, 16 and 17 is equal to eight minus the number of electrons in their respective valence shells.

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