NCERT Class X Science Class: Chapter –5. Periodic Classification of Elements – Part-7

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Question 33:

Three elements A, B and C have 3, 4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the Modern Periodic Table. Also, give their valences.

Answer:

Table of Element and Valency
Three elements A, B and C have 3, 4 and 2

Element

Group No.

Valency

A

Group-13

3

B

Group-14

4

C

Group-2

2

Question 34:

If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?

Answer:

As the element X is placed in group 14 then the valency of the element is 4.

Now we know that the valency of chlorine is 1 as it’s atomic number is 17.

Therefore, as the element X has the valency 4 it can neither gain nor lose electrons to attain octet.

Therefore, it makes a covalent bonding with four atoms of chlorine to form a compound .

Question 35:

Compare the radii of two species X and Y. Give reasons for your answer.

  1. X has 12 protons and 12 electrons

  2. Y has 12 protons and 10 electrons

Answer:

From electron arrangement

Since Y has fewer energy levels its atomic radius will be smaller than that of X.

Note:

X and Y have the same no. of protons

Y is actually an ion of X obtained when X loses the two electrons in its outermost energy level.

Question 36:

Arrange the following elements in increasing order of their atomic radii.

Answer:

As the atomic radii decreases along a period

Thus, the given elements will be arranged in the following order

As the atomic radii increases down a group

Thus, the given elements will be arranged in the following order

Question 37:

Identify and name the metals out of the following elements whose electronic configurations are given below.

Answer:

  1. Magnesium

  2. Sodium

  3. Chlorine

  4. Lithium

Metals are (a) Magnesium, (b) Sodium and (d) Lithium as they have 1 to 3 valence electrons. Whereas, (c) chlorine is a non-metal.

Question 38:

Write the formula of the product formed when the element A (atomic number 19) combines with the element B (atomic number 17). Draw its electronic dot structure. What is the nature of the bond formed?

Answer:

The electron configuration of elements A with atomic number 19 is 2,8,8,1

Therefore valance electron is q and valency will be 1

The electronic configuration of elements B with atomic number 17 is 2,8,7

Therefore, valance is electron is 7 and valency will be 1 hey need one electron to complete the octet

Chemical formula between the A and B is AB

Imagee electronic dot structure of AB

Imagee Electronic Dot Structure of AB

Imagee electronic dot structure of AB

Ionic bond.

A = K (Potassium) B = Cl (Chlorine)