Chapter 4.1 – Matter: Atomic structure physical and chemical properties of matter | Chapter Solution Class 9

Publisher	: Santra publication pvt. ltd.
Book Name	: Madhyamik Physical Science And Environment
Class	: 9 (Madhyamik)
Subject	: Physical Science
Chapter Name	: Matter: Atomic structure physical and chemical properties of matter

Multiple Choice Questions (MCQ)

[Each of Mark-1]

Question 1

The smallest part of an element that retains the chemical properties of the element

1. electron
2. molecule
3. atom
4. proton

Answer

atom

Explanation

An atom is the basic unit of matter that retains the chemical properties of an element. It consists of a central nucleus made up of positively charged protons and neutral neutrons, surrounded by a cloud of negatively charged electrons.

Question 2

Electron was discovered by

1. William Crookes
2. A. Arrhenius
3. Michael Faraday
4. J. J. Thomson

Answer

J.J. Thomson

Explanation

The discovery of the electron is attributed to J.J. Thomson.

Question 3

Cathode rays are composed of

1. radiation
2. thermal radiation
3. beam of negatively charged particles
4. positively charged particles

Answer

beam of negatively charged particles

Explanation

Cathode rays are produced when an electric current is passed through a vacuum tube containing a cathode (a negatively charged electrode) and an anode (a positively charged electrode).

Question 4

Cathode rays are deflected under the influence of electromagnetic fields because cathode rays are

1. electromagnetic radiation (EMR i.e. light)
2. positively charged particles
3. beam of neutral particles
4. beam of electrons

Answer

beam of electrons

Explanation

When an electromagnetic field is applied to a beam of electrons, the electrons experience a force that causes them to deviate from their original path. This phenomenon is known as electron deflection.

Question 5

In a perforated cathode ray tube, other rays, other than cathode rays were found. These rays are

1. protons
2. electrons
3. radiation
4. neutrons

Answer

protons

Explanation

In a perforated cathode ray tube, other rays found were positively charged canal rays (protons), also called anode rays.

Question 6

Who got Nobel Prize twice?

1. Rutherford
2. Bohr
3. Einstein
4. Marie Curie

Answer

Marie Curie

Explanation

Marie Curie is the only person to have received Nobel Prizes in two different fields – Physics (1903) and Chemistry (1911) – for her pioneering work on radioactivity.

Question 7

Radioactivity was discovered by

1. Rutherford
2. Becquerel
3. Marie Curie
4. Pierre Curie

Answer

Henri Becquerel

Explanation

Radioactivity was discovered by Henri Becquerel in 1896. While investigating the properties of fluorescent materials, he accidentally discovered that uranium salts emitted penetrating rays that could expose photographic plates.

Question 8

Radioactivity was first recognised while working with which element?

1. Uranium
2. Thorium
3. Polonium
4. Barium

Answer

uranium

Explanation

Radioactivity was first recognized while working with uranium. In 1896, Henri Becquerel discovered that uranium salts emitted penetrating rays that could expose photographic plates, leading to the discovery of radioactivity.

Question 9

The concept of the nucleus of an atom was given by

1. J. J. Thomson
2. Niels Bohr
3. Rutherford
4. M. Curie

Answer

Ernest Rutherford

Explanation

The concept of the nucleus of an atom was given by Ernest Rutherford in 1911. He proposed that most of the mass of an atom was concentrated in a tiny, positively charged nucleus.

Question 10

The diameter of the nucleus is of the order of

1. 10^-3 cm 
2. 10^-23 cm
3. 10³ cm
4. 10^-13 cm

Answer

10^-13 cm

Explanation

The diameter of the nucleus is of the order of 10^-13 cm or 1 femtometer. This is about 100,000 times smaller than the diameter of the atom, which is primarily due to the presence of the nucleus.

Question 11

From the fact then a helium atom is four times as heavy as a hydrogen atom. Rutherford predicted the existence of

1. proton
2. isotope
3. neutron
4. nucleus

Answer

neutron

Explanation

From the fact that a helium atom is four times as heavy as a hydrogen atom, Rutherford predicted the existence of a neutral particle in the nucleus, which he called a neutron. The neutron was later discovered by James Chadwick in 1932.

Question 12

Study of sun spectra, the element first identified is

1. helium
2. hydrogen
3. uranium
4. gold

Answer

helium

Explanation

The element first identified in the study of sun spectra is helium. In 1868, French astronomer Jules Janssen and English astronomer Joseph Lockyer observed a yellow spectral line that was later identified as helium.

Question 13

Which of the following concepts is not connected to Bohr’s model ?

1. Circular shell or orbit
2. quantization
3. line spectra of hydrogen
4. nuclear force

Answer

Nuclear force

Explanation

Nuclear force is not connected to Bohr’s model. Bohr’s model of the atom proposed that electrons move in circular orbits around the nucleus, explaining the quantization of energy and the line spectra of hydrogen.

Question 14

An electron in a Bohr’s orbit is associated with definite

1. radius
2. velocity
3. energy
4. all the above

Answer

energy

Explanation

An electron in a Bohr’s orbit is associated with definite energy. According to Bohr’s model of the atom, electrons move in circular orbits around the nucleus and can occupy only certain allowed energy levels, corresponding to specific orbits.

Question 15

Ionization energy of the hydrogen atom, as calculated (by Bohr) and experimentally obtained, is

1. 13.56 eV
2. 13.56 J
3. 13.56 Cal
4. none of these

Answer

13.56 eV

Explanation

The ionization energy of the hydrogen atom, as calculated by Bohr and experimentally obtained, is 13.56 eV (electron volts).

Question 16

Which of the following is considered a limitation of Bohr’s model? It was unable to explain

1. E_n i.e. energy of the nth shell electron of hydrogen
2. ionization energy of hydrogen
3. line spectrum of helium
4. line spectrum of hydrogen

Answer

line spectrum of helium

Explanation

Bohr’s model was unable to explain the line spectrum of atoms other than hydrogen. While it successfully explained the line spectrum of hydrogen, it failed to account for the more complex spectra of other elements, such as helium.

Question 17

On which of the following, Rutherford’s model differs from Bohr’s model?

1. the circular shape of the orbit
2. concept of nucleus
3. empty space in an atom
4. stability of an atom

Answer

stability of an atom

Explanation

Rutherford’s model and Bohr’s model differed in their explanation of the stability of an atom. Rutherford’s model did not address the issue of why the electrons did not radiate their energy and spiral into the nucleus, while Bohr’s model proposed that electrons could only occupy certain allowed energy levels, corresponding to specific orbits, which prevented them from radiating their energy and collapsing into the nucleus.

Question 18

Which of the following is true? [A = mass number, Z = atomic number, N = number of neutron]

1. A = Z
2. A = Z-N
3. A = Z+N
4. A = N – Z

Answer

A = Z + N

Explanation

The relationship between the mass number (A), atomic number (Z), and number of neutrons (N) is A = Z + N. The mass number represents the total number of protons and neutrons in the nucleus of an atom, while the atomic number represents the number of protons. The number of neutrons can be calculated as N = A – Z.

Question 19

Isotopes of an element has the same

1. mass number (A)
2. number of neutrons
3. number of protons
4. number of protons but not electrons

Answer

number of protons

Explanation

Isotopes of an element have the same number of protons (atomic number) but different mass numbers (A) due to a different number of neutrons. Isotopes also have the same chemical properties but different physical properties.

Question 20

Isotones are atoms with the same number of

1. neutrons
2. protons
3. electrons
4. mass number

Answer

neutrons

Explanation

Isotones are atoms with the same number of neutrons but different numbers of protons and different atomic numbers. Isotones have similar nuclear properties but different chemical properties due to their different atomic numbers.

Question 21

Isobars are atoms having the same number of

1. protons
2. neutrons
3. electrons
4. protons + neutrons

Answer

protons + neutrons

Explanation

Isobars are atoms having the same mass number (A), which means they have the same total number of protons and neutrons, but different atomic numbers (Z) and different numbers of protons. Isobars have different chemical properties due to their different atomic numbers.

Question 22

Mass of a ¹²C isotope, in amu unit, is

1. 1
2. 12
3. 1/12
4. none of them

Answer

12

Explanation

The mass of a ¹²C isotope, in amu (atomic mass unit), is 12. The atomic mass unit is defined as one-twelfth of the mass of a neutral atom of carbon-12, which has 6 protons and 6 neutrons in its nucleus.

Question 23

The ground state electron configuration of potassium (Z = 19) is

1. 2, 8, 8, 1
2. 2, 8, 9, 0
3. 2, 9, 8, 0
4. 2, 7, 8, 2

Answer

2, 8, 8, 1

Explanation

The ground state electron configuration of potassium (Z = 19) is 2, 8, 8, 1. This means that there are two electrons in the first energy level, eight in the second energy level, eight in the third energy level, and one in the fourth energy level.

Answer in one word or in one sentence

[Each of Mark-1]

Question

1. What force is responsible for holding together the particles in the nucleus ?
2. There are 2,8 and 7 electrons in the shells K, L, and M, respectively. If the mass number of the atom is 37, what is the number of neutrons ?
3. What are the particles in the nucleus in an atom?
4. Give an example of an atom, in the nucleus of which, there is no neutron.
5. Name the heaviest particle that occurs in the nucleus.
6. Number of electrons and neutrons in an atom are 6 and 8 respectively. What is the mass number of the atom ?
7. Atomic number of Mg is 12; give the number of electrons it Mg²⁺ ion.
8. Na losses one electron to form Na⁺ ion. From which shell K, L or M that electron is released?
9. In which part of an atom, do the protons occurs?
10. Give the number of neutrons in the ²³⁵U isotope.
11. There are 7 electrons in the outermost shell (L) of an atom. Give its atomic number.
12. Give the charge of the particle neutron.
13. How many times a proton is heavier than the electron?
14. What is the relation between nuclear charges and the atomic number?
15. Deuterium is a naturally occurring isotope of which element?
16. A beam of protons or electrons, which will be deflected more under an electric field?
17. The atomic number of Aluminium is 13. Give the electron configuration of Al³⁺ ion.
18. Mg and Mg²⁺, which one is more stable and which one has more electrons?
19. An atom has 3 electrons in the M-shell (third shell). Mention the atomic number of the atom.
20. Mention one of the natural spectrums.

Answer

1. Nuclear force
2. 20
3. Protons and neutrons
4. Hydrogen-1 (protium)
5. Neutron
6. 14
7. 10
8. M shell
9. Nucleus
10. 143
11. 7
12. Neutral
13. 1836 times
14. They are equal
15. Hydrogen
16. Electrons
17. 2, 8
18. Mg²⁺ is more stable and has fewer electrons
19. 13
20. Visible spectrum

Short answer type questions

[Each of Mark-2]

Question 1

The atomic number and atomic mass of carbon are 6 and 12 respectively. Give the structure of the atom.

Answer

Number of proton = 6

Number of electron = 6

Number of nucleus = 12 – 6 = 6

 

Question 2

Why the atomic mass of chlorine is a fraction, 35.5 ?

Answer

The atomic mass of chlorine is a fraction because it is an average of the masses of its two stable isotopes, chlorine-35 and chlorine-37, which occur in different proportions in nature.

Question 3

Mention the mutual relation between ³⁵A₁₇ and ³⁷B₁₇. How many electrons, protons and neutrons are there in each of them?

Answer

³⁵A₁₇ and ³⁷B₁₇ are isotopes of the same element, chlorine. Both isotopes have 17 protons and 17 electrons, but ³⁵A₁₇ has 18 neutrons and ³⁷B₁₇ has 20 neutrons in their respective nuclei.

Question 4

Differentiate between atomic number and mass number.

Answer

Atomic Number	Mass Number
Represents the number of protons in an atom	Represents the total number of protons and neutrons in an atom
Determines the element to which the atom belongs	Determines the isotopes of the element

Question 5

³⁵A₁₇ and ³⁷B₁₇, do they differ in chemical behaviour?

Answer

Yes, ³⁵A₁₇ and ³⁷B₁₇ differ in chemical behaviour due to the difference in their atomic masses. This can affect their physical and chemical properties, such as boiling point, melting point, reactivity, and bonding behaviour.

Question 6

₈O¹⁶, what does it mean? Write its electronic configuration.

Answer

₈O¹⁶ represents the isotope of oxygen with atomic number 8 and mass number 16, which means it has 8 protons and 8 neutrons in its nucleus.

The electronic configuration of oxygen (O) is 2, 8

Question 7

Define the term ‘isotope’. Express the two isotopes of hydrogen by the symbol.

Answer

Isotopes are atoms of the same element that have the same number of protons (atomic number) but a different number of neutrons (mass number). The two isotopes of hydrogen are represented by the symbols ₁H (protium) and ₂H (deuterium).

Question 8

Define atomic mass with reference to the ¹²C scale.

Answer

Atomic mass is defined as the mass of an atom relative to the mass of a carbon-12 atom, which is assigned a mass of exactly 12 atomic mass units (amu) on the ¹²C scale.

Question 9

Compare the relative charges and masses of a proton, a neutron, and an electron.

Answer

Particle	Relative Charge	Relative Mass
Proton	+1	1
Neutron	0	1
Electron	-1	1/1836

Question 10

Explain the meaning of the scale of atomic masses. 

Answer

The atomic mass scale is a system used to express the relative masses of atoms and molecules, with the mass of a carbon-12 atom being assigned a mass of exactly 12 atomic mass units (amu).

Question 11

Compare the mass of an atom to that to the mass of its nucleus.

Answer

The mass of an atom is primarily due to the mass of its nucleus, which contains protons and neutrons. The mass of electrons, which are much lighter, is negligible compared to the mass of the nucleus. The nucleus typically makes up more than 99.9% of the total mass of the atom.

Question 12

Which one of the atomic number and atomic mass, is the fundamental property of an element? Why?

Answer

Atomic number is the fundamental property of an element because it is based on the number of protons in the nucleus, which uniquely identifies the element and determines its chemical properties. Atomic mass can vary due to the presence of different isotopes.

Question 13

Give the diagrams of the different isotopes of chlorine.

Answer

(a) Chlorine-35 (17 protons, 18 neutrons):

(b) Chlorine-37 (17 protons, 20 neutrons):

Question 14

In ₉₂X²³⁵, how many of electrons, protons and neutrons are there ?

Answer

The isotope ₉₂X²³⁵ represents an atom of uranium.

In this isotope:

• The number of protons (atomic number) is 92
• The number of electrons in a neutral atom is also 92
• The number of neutrons is equal to the mass number minus the atomic number: 235 – 92 = 143

Therefore, this isotope has 92 protons, 92 electrons, and 143 neutrons.

Question 15

Give the electronic configuration of an atom having atomic number 13.

Answer

2, 8, 3

Question 16

₁H¹, ₁H² and ₁H³, what is the mutual relation among them? In which of them, there is no neutron?

Answer

₁H¹, ₁H², and ₁H³ are isotopes of hydrogen, meaning they have the same number of protons (1) but different numbers of neutrons (0, 1, and 2, respectively). ₁H¹ (hydrogen-1 or protium) is the only isotope of hydrogen that has no neutrons in its nucleus.

Question 17

Mass numbers of 3 atoms are 31, 32 and 34, having numbers of neutron 16, 17 and 18 respectively. Which two of them are isotopes and why?

Answer

The two atoms with mass numbers 32 and 34 are isotopes because they have the same number of protons (since they are both of the same element) but different numbers of neutrons (17 and 18, respectively). The atom with mass number 31 is a different element since it has one fewer proton.

Question 18

Differentiate between an atom and an ion.

Answer

Atom	Ion
Neutral particle with equal numbers of protons and electrons	Charged particle with unequal numbers of protons and electrons
May or may not have valence electrons	Always has valence electrons gained or lost in the process of ionization

Question 19

Explain with an example: Isotopes, why are they similar in chemical properties?

Answer

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. They are similar in chemical properties because they have the same number of valence electrons, which determine an element’s chemical behavior. For example, carbon-12 and carbon-14 are isotopes of carbon, and they both react with oxygen to form carbon dioxide.

Question 20

The percentage of occurrence in a sample of ₅Y¹⁰ and ₅Y¹¹ are 20% and 80% respectively. Find the atomic mass of the element.

Answer

The atomic mass of the element can be calculated using the formula:

(average atomic mass) = (mass of isotope 1 × abundance of isotope 1) + (mass of isotope 2 × abundance of isotope 2)

Given that the sample contains 5 atoms each of Y10 and Y11, we can calculate the masses of the isotopes as:

Mass of Y¹⁰ = 5 atoms × 10 atomic mass units (amu)

= 50 amu

Mass of Y¹¹ = 5 atoms × 11 atomic mass units (amu)

= 55 amu

Using the given percentages of occurrence, we can calculate the abundances of each isotope as:

Abundance of Y¹⁰ = 20% = 0.2 Abundance of Y¹¹ = 80% = 0.8

Substituting these values in the formula, we get:

(average atomic mass) = (10 amu × 0.2) + (11 amu × 0.8)

= 2 amu + 8.8 amu

= 10.8 amu

Therefore, the atomic mass of the element is approximately 10.8 atomic mass units.

Long answer type questions

[Each of Mark-3]

Question 1

Mention two similarities and two differences between ₁₇Cl³⁵ and ₁₇Cl³⁷.

Answer

Two similarities and two differences between ₁₇Cl³⁵ and ₁₇Cl³⁷ are:

Similarities:

1. Both are isotopes of chlorine and have the same atomic number of 17.
2. Both have the same number of electrons and the same electronic configuration.

Differences:

1. ₁₇Cl³⁵ has 18 neutrons, while ₁₇Cl³⁷ has 20 neutrons.
2. ₁₇Cl³⁵ has a lower atomic mass of 35 amu, while ₁₇Cl³⁷ has a higher atomic mass of 37 amu.

Question 2

Mention the numbers of protons and neutrons in ₆A¹³. Write down the electron configuration of it. What differences are there in the nuclear structure of ₆A¹³ and ₆A¹²? Are they chemically similar? Why?

Answer

The atomic number of ₆A¹³ is 6, which means it has 6 protons. The mass number of 13 indicates that it has 13 – 6 = 7 neutrons.

The electron configuration of ₆A¹³ = 2, 4

The nuclear structure of ₆A¹³ and ₆A¹² differs by the number of neutrons in their respective nuclei. ₆A¹³ has 7 neutrons while ₆A¹² has 6 neutrons. The presence of an extra neutron in ₆A¹³ changes the nuclear properties of the atom such as nuclear spin, magnetic moment, and binding energy.

Despite having different nuclear structures, ₆A¹³ and ₆A¹² are chemically similar as they have the same number of protons and electrons, which determines the chemical behaviour of an element. Both isotopes will have the same valence electron configuration and similar chemical properties.

Question 3

What is an ‘ion’ ? Mention its types. Write the electronic configuration of Mg (Z = 12).

Answer

An ion is an electrically charged particle that is formed when an atom gains or loses one or more electrons. There are two types of ions:

1. Cations: positively charged ions formed by losing electrons.
2. Anions: negatively charged ions formed by gaining electrons.

The electronic configuration of Mg (Z = 12) is: 2, 8, 2.

Question 4

How are atoms ₁₇A³⁵ and ₁₇B³⁷ related? How many neutrons are there in each of them?

Answer

Atoms ₁₇A³⁵ and ₁₇B³⁷ are isotopes of the same element with the same atomic number (17), but different mass numbers (35 and 37). They differ in the number of neutrons in their nuclei.

In ₁₇A³⁵, there are 17 protons and 18 neutrons.

In ₁₇B³⁷, there are 17 protons and 20 neutrons.

Question 5

₂₀X⁴⁰, mention the numbers of protons and neutrons of the atom. Give the electronic configuration.

Answer

Number of proton = 20

Number of neutrons = 40 – 20 = 20

Electronic configuration = 2, 8, 8, 2

Question 6

What do you mean by gram atomic mass? Give example.

Answer

Gram atomic mass refers to the mass of one mole of atoms of a particular element, expressed in grams. For example, the gram atomic mass of carbon is 12.01 g/mol, which means that one mole of carbon atoms has a mass of 12.01 grams.

Question 7

From which part of an atom, does an alpha particle come from? Give reason.

Answer

An alpha particle is a helium nucleus, which means that it consists of two protons and two neutrons. These particles are produced from the nucleus of an atom during alpha decay. Hence, alpha particles come from the nucleus of an atom.

Question 8

Explain why some a-particles will be deflected through large angles when a beam of a-particles is directed at a thin gold foil. 

Answer

When a beam of alpha particles is directed at a thin gold foil, some alpha particles will be deflected through large angles because the gold atoms in the foil have a positively charged nucleus that repels the positively charged alpha particles. The deflection occurs due to the electrostatic repulsion between the positively charged nucleus and the positively charged alpha particle, causing them to scatter at large angles.

Question 9

Mention the limitations of Rutherford model of atomic structure. Also mention the merits of it.

Answer

Limitations of Rutherford model:

• It could not explain the distribution of electrons in an atom.
• It could not explain the stability of atoms with multiple electrons.
• It could not explain the spectra of atoms with more than one electron.

Merits of Rutherford model:

• It introduced the concept of a central, positively charged nucleus in an atom.
• It provided evidence for the existence of atomic particles such as protons and neutrons.
• It allowed for the understanding of nuclear reactions and the transmutation of elements.

Question 10

Mention the merits of Bohr’s model of atomic structure. What are the old and new concept Bohr introduced in his model?

Answer

Merits of Bohr’s model:

• Explained the stability of an atom by quantizing electron energy levels.
• Successfully explained the atomic spectra of hydrogen.
• Introduced the concept of quantization of angular momentum.
• Opened the path for the development of quantum mechanics.

Old concept	New concept
Electron orbits the nucleus	Electrons move in fixed circular orbits of specific energy levels
No explanation for the stability of the atom	Explains the stability of an atom
No explanation for the origin of the spectral lines	Explains the origin of the spectral lines by the transitions of electrons between different energy levels
Electrons can lose energy continuously	Electrons can only lose or gain energy by jumping from one energy level to another in a discrete way