Structure of the Atom NCERT Solution, study material, CBSE Notes

NCERT Solution: Structure of the Atom

If bromine atom is available in the form of, say, two isotopes (49.7%) and (50.3%), calculate the average atomic mass of bromine atom.

It is given that two isotopes of bromine are (49.7%) and (50.3%). Then, the average atomic mass of bromine atom is given by:

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes and in the sample?

It is given that the average atomic mass of the sample of element X is 16.2 u.

Let the percentage of isotope be y %. Thus, the percentage of isotope will be (100 - y) %.

Therefore,

Therefore, the percentage of isotopeis 10%.

And, the percentage of isotopeis (100 - 10) % = 90%.

If Z = 3, what would be the valency of the element? Also, name the element.

By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron).
Therefore, the element with Z = 3 is lithium.

Composition of the nuclei of two atomic species X and Y are given as under

                 X              Y
Protons = 6              6
Neutrons = 6             8
Give the mass numbers of X and Y. What is the relation between the two species?

Answer

Mass number of X = Number of protons + Number of neutrons

= 6 + 6
= 12

Mass number of Y = Number of protons + Number of neutrons
= 6 + 8
= 14

These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes.

For the following statements, write T for 'True' and F for 'False'.

(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
► False

(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
► False

► True

(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

► False

Rutherford's alpha-particle scattering experiment was responsible for the discovery of

Rutherford's alpha-particle scattering experiment was responsible for the discovery of
(a) Atomic nucleus
(b) Electron
(c) Proton
(d) Neutron
ANS (a) Atomic nucleus

Isotopes of an element have

Isotopes of an element have
(a) the same physical properties
(b) different chemical properties
(c) different number of neutrons
(d) different atomic numbers
ANS (c) different number of neutrons

Number of valence electrons in Cl ^-ion are:

Number of valence electrons in Cl ^-ion are:
(a) 16
(b) 8
(c) 17
(d) 18
ANS (b) 8