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Standard VIII
Chemistry
Question

The valency of elements in the periodic table with respect to hydrogen:
  1. increases regularly from 1 to 8
  2. decreases regularly from 1 to 8
  3. first increases from group I to group IV and then decreases
  4. first decreases from group I to group IV and then increases

A
first increases from group I to group IV and then decreases
B
first decreases from group I to group IV and then increases
C
increases regularly from 1 to 8
D
decreases regularly from 1 to 8
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Solution
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Valency is mainly concerned with number of valence electrons or 8 minus number of electrons present in the outermost shell. Number of valence electrons increases upto group IV and then starts decreasing due to addition of electrons in the same shell.

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Similar Questions
Q1

(i) Electropositive nature of the element(s) increases down the group and decreases across the period
(ii) Electronegativity of the element decreases down the group and increases across the period
(iii) Atomic size increases down the group and decreases across a period (left to right)
(iv) Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.

Name the element which shows maximum valency.


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Q2

Parts (a) to (e) refer to changes in the properties of elements on moving from left to right across a period of Periodic Table. For each property, choose the correct answer.

(a) The non-metallic character of the elements :

(i) decreases, (ii) increases,

(iii) remains the same, (iv) depends on the period

(b) The electronegativity :

(i) depends on the number of valence electrons,

(ii) remains the same,

(iii) decreases,

(iv) increases.

(c) The ionization potential :

(i) goes up and down (ii) decreases

(iii) increases (iv) remains the same

(d) The atomic size :

(i) decreases,

(ii) increases,

(iii) remains the same ,

(iv) sometimes increases and sometimes decreases.

(e) The electron affinity of the elements in groups 1 to 7 :

(i) goes up and then down.

(ii) decreases and then increases,

(iii) increases,

(iv) decreases.

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Q3

Give scientific reasons:

1. Atomic size increases down the group.

2. Metallic character decreases from left to right in a period.

3. Elements in the same group show same valency.

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Q4

(i) Electropositive nature of the element(s) increases down the group and decreases across the period
(ii) Electronegativity of the element decreases down the group and increases across the period
(iii) Atomic size increases down the group and decreases across a period (left to right)
(iv) Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.

Name the element which is a metalloid


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Q5

Explain the following
(i) Electronegativity of elements increase on moving from left to right in the periodic table.

(ii) Ionisation enthalpy decreases in a group from top to bottom.

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