Structure Of An Atom(9th Grade > Chemistry ) Questions and answers for exam Preparation

9th Grade > Chemistry

STRUCTURE OF AN ATOM MCQs

Total Questions : 53 | Page 4 of 6 pages

Question 31.

Which of the following are isotopes?

$_{1}^{1} H$ , $_{1}^{2} H$ , $_{1}^{3} H$
$_{20}^{40} C a$ , $_{18}^{40} A r$
$_{6}^{12} C$ , $_{6}^{13} C$ , $_{6}^{14} C$
$_{26}^{58} F e$ , $_{27}^{58} N i$

Discuss Question

Answer: Option A. ->

_{1}^{1} H

_{1}^{2} H

_{1}^{3} H

:
A and C

∙

Isotopes have the same atomic number (same number of protons) and different mass number.

∙

Since,

_{1}^{1} H

_{1}^{2} H

_{1}^{3} H

have the same atomic number, they are isotopes of hydrogen.

∙

Similarly,

_{6}^{12} C

_{6}^{13} C

_{6}^{14} C

have same atomic number, hence they are isotopes of carbon.

∙

Whereas,

_{20}^{40} C a

_{18}^{40} A r

and

_{26}^{58} F e

_{27}^{58} N i

have different atomic numbers and hence, are not isotopes. They are isobars as they have same mass number.

Question 32.

Which of the following are the postulates of Thomson’s model of an atom?

An atom consists of a positively charged sphere and electrons are embedded in it.
The negative and positive charges are equal in magnitude.
An atom consists of a positively charged sphere and electrons are embedded in it, the positive and negative charges are equal in magnitude.
An atom consists of a negatively charged sphere and neutrons are embedded in it.

Discuss Question

Answer: Option C. -> An atom consists of a positively charged sphere and electrons are embedded in it, the positive and negative charges are equal in magnitude.
:
C

Thomson proposed that :

1) An atom consists of a positively charged sphere and the electrons are embedded in it.

2) The negative and positive charges are equal in magnitude.

From above two we can say that the atom as a whole is electrically neutral.

Question 33.

Which fundamental particle is not present in the nucleus of a hydrogen atom?

Neutrons
Electrons
Protons
Photons

Discuss Question

Answer: Option A. -> Neutrons
:
A
Neutrons are fundamental sub-atomic particles present in the nucleus of an atom. Hydrogen is the only element which is devoid of neutrons.

Question 34.

Thomson's atomic model could not explain the result of scattering experiment performed by Rutherford.

True
False

Discuss Question

Answer: Option A. -> True
:
A

According to Thomson's atomic model, the positive charge is uniformly distributed in the sphere and electrons are embedded in it just like a plum pudding.This implies that when alpha particles are bombarded on the atoms, they should get deflected uniformly.
However, in the Rutherford alpha particle scattering experiment, it was found that rays were deflected in various angles.

Question 35.

Which of the following are properties of anode rays?

Anode rays deflect towards negatively charged plate
Anode rays travel along a straight path in absence of electric and magnetic field
Anode rays are positively charged radiations due to positive charged sub-atomic particles
All of these

Discuss Question

Answer: Option D. -> All of these
:
D

Following are the properties of anode rays:

1) Anode rays deflect towards negatively charged plate.

2) Anode rays travel along a straight path in absence of electric and magnetic field.

3) Anode rays are positively charged radiations due to positive charged sub-atomic particles.

Question 36.

_______ atomic model is also known as the plum pudding model.

Thomson's
Rutherford's
Bohr's
Dalton's

Discuss Question

Answer: Option A. -> Thomson's
:
A
J. J. Thomson proposed the plum pudding model.
According to him, the negatively charged electrons were distributed in a sea of positive charge. This model, shown below, resembled to a plum pudding.

Question 37.

The mass of the electrons is negligible when compared to protons.

True
False
Bohr's
Dalton's

Discuss Question

Answer: Option A. -> True
:
A
Atoms have electrons, protons, and neutrons as the fundamental particles.

\begin{matrix} Subatomic particle & Mass (kg) Proton & 1.67262178 \times 10^{- 27} Neutron & 1.6749 \times 10^{- 27} Electron & 9.10938291 \times 10^{- 31} \end{matrix}

\frac{M a s s o f p r o t o n}{M a s s o f e l e c t r o n}

\frac{1.67262178 \times 10^{- 27}}{9.10938291 \times 10^{- 31}}

= 1840
Thus, mass of electron is

\frac{1}{1840}

, i.e., 0.0005 times that of proton.
Hence, the mass of an electron is negligible when compared to the mass of proton.

Question 38.

Identify the conclusions from the Rutherford's alpha ray scattering experiment.

The centre of the atom is empty space
Most of the volume of the atom is empty
The center of the atom has only negative charge
Atomic mass is concentrated at the centre of the atom

Discuss Question

Answer: Option B. -> Most of the volume of the atom is empty
:
B and D

According to Rutherford, the atoms are made of two parts: the nucleus and the extra-nuclear part. His experiments proved that the atom is largely empty and has a heavy positively-charged body at the centre called the nucleus. The central nucleus is positively-charged and the negatively-charged electrons revolve around the nucleus.

Question 39.

Name the scientist who first measured the e/m ratio of an electron.

J. J Thomson
James Chadwick
Dalton
Rutherford

Discuss Question

Answer: Option A. -> J. J Thomson
:
A

J.J Thomson was the first scientist who measured charge to mass ratio(e/m) of an electron. When a narrow beam of charged particles are projected at constant speed (v) across a magnetic field in a direction perpendicular to the field, the beam of particles experiences a force, which makes them move in a circular path.

Question 40.

The charge on an electron is _______ coulombs.