Question

What information do you get from the figure about the atomic number, mass number and valency of atoms $X, Y$ and $Z$ ? Give your answer in a tabular form.

Accepted Answer

For the element $X$ ,

The atomic number will be equal to $5$ which is obtained from the number of protons. Mass number is the sum of number of protons and neutrons. Therefore, the mass number of $X = 5 + 6 = 11$ . The element $X$ has three electrons in its outermost shell. Therefore, it loses $3$ electrons and forms a cation to complete its octet. Therefore, its valency is $3$ .

For the element $Y$ ,

The atomic number will be equal to $8$ which is obtained from the number of protons.The mass number of $Y = 8 + 10 = 18$ . The element $Y$ has six electrons in its outermost shell. Therefore, it gains two more electrons to attain the nearest noble gas configuration. Therefore, its valency is $2$ .

For the element $Z$ ,

The atomic number will be equal to $15$ which is obtained from the number of protons.The mass number of $Z = 15 + 16 = 31$ . The element $Z$ has five electrons in its outermost shell. It can either gain three electrons and can form an anion to complete its octet or it can lose five electrons and form a cation to complete its octet. Therefore, it can have the valencies of $3$ and $5$ .

That is, the values can be tabulated as,

Element Atomic number Mass number Valency

$X$ $5$ $11$ $3$

$Y$ $8$ $18$ $2$

$Z$ $15$ $31$ $3, 5$

Column A	Column B
(a)Ernest Rutherford	(i) Indivisibility of atoms
(b) JJ. Thomson	(ii) Stationary orbits
(c) Dalton	(iii) Concept of nucleus
(d) Niels Bohr	(iv) Discovery of electrons
(e) James Chadwick	(v) Atomic number
(f) E. Goldstein	(vi) Neutron
(g) Moseley	(vii) Canal rays

NCERT Solutions for Chapter: Structure Of The Atom, Exercise 2: Short Answer Questions

NCERT Science Solutions for Exercise - NCERT Solutions for Chapter: Structure Of The Atom, Exercise 2: Short Answer Questions

Questions from NCERT Solutions for Chapter: Structure Of The Atom, Exercise 2: Short Answer Questions with Hints & Solutions

Learn and Prepare for any exam you want !

Element	$n_{p}$	$n_{n}$