Match the atomic numbers 4, 8, 10, 15 and 19 with each of the following: (a) Element which can form trivalent ion (b) An element with 4 shells. (c) Element with 6 valence electrons. (d) Element which does not form ion.

 Question:

Match the atomic numbers 4, 8, 10, 15 and 19 with each of the following:

(a)         Element which can form trivalent ion

(b)         An element with 4 shells.

(c)          Element with 6 valence electrons.

(d)         Element which does not form ion.

Solution:

(a)         15

(b)         19

(c)          8

(d)         10

Explanation:

First, write their electronic configuration

4- 2, 2

8- 2, 6

10- 2, 8

15- 2, 8, 5

19- 2, 8, 8, 1

(a) Trivalent ion means it will have charge 3, which means that it will gain or lose 3 electrons. Element with atomic number 15 has 5 electrons in its valence shell, so it will gain 3 electrons to have 8 electrons in its last shell. Thus the answer is 15.

(b) It is clear from the electronic configurations that only the element with atomic number 19 has 4 shells. Others have 2 or 3 shells.

(c) It is clear from the electronic configurations that element with atomic number

4 has 2 valence electrons

8 has 6 valence electrons

10 has 8 valence electrons

15 has 5 valence electrons

19 has 1 valence electron

So the correct answer is 8.

(d) It does not form ion means that it is already stable which means that it has 8 electrons in its last shell.  Again from the electronic configurations, such an element is the one with atomic number 10.