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 |
Table of Contents
ToggleMultiple Choice Questions (MCQ)
[Each of Mark-1]
Question 1
The smallest part of an element that retains the chemical properties of the element
- electron
- molecule
- atom
- 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
- William Crookes
- A. Arrhenius
- Michael Faraday
- 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
- radiation
- thermal radiation
- beam of negatively charged particles
- 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
- electromagnetic radiation (EMR i.e. light)
- positively charged particles
- beam of neutral particles
- 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
- protons
- electrons
- radiation
- 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?
- Rutherford
- Bohr
- Einstein
- 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
- Rutherford
- Becquerel
- Marie Curie
- 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?
- Uranium
- Thorium
- Polonium
- 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
- J. J. Thomson
- Niels Bohr
- Rutherford
- 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
- 10-3 cm
- 10-23 cm
- 103 cm
- 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
- proton
- isotope
- neutron
- 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
- helium
- hydrogen
- uranium
- 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 ?
- Circular shell or orbit
- quantization
- line spectra of hydrogen
- 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
- radius
- velocity
- energy
- 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
- 13.56 eV
- 13.56 J
- 13.56 Cal
- 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
- En i.e. energy of the nth shell electron of hydrogen
- ionization energy of hydrogen
- line spectrum of helium
- 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?
- the circular shape of the orbit
- concept of nucleus
- empty space in an atom
- 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]
- A = Z
- A = Z-N
- A = Z+N
- 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
- mass number (A)
- number of neutrons
- number of protons
- 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
- neutrons
- protons
- electrons
- 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
- protons
- neutrons
- electrons
- 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
- 12
- 1/12
- 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
- 2, 8, 8, 1
- 2, 8, 9, 0
- 2, 9, 8, 0
- 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
- What force is responsible for holding together the particles in the nucleus ?
- 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 ?
- What are the particles in the nucleus in an atom?
- Give an example of an atom, in the nucleus of which, there is no neutron.
- Name the heaviest particle that occurs in the nucleus.
- Number of electrons and neutrons in an atom are 6 and 8 respectively. What is the mass number of the atom ?
- Atomic number of Mg is 12; give the number of electrons it Mg2+ ion.
- Na losses one electron to form Na+ ion. From which shell K, L or M that electron is released?
- In which part of an atom, do the protons occurs?
- Give the number of neutrons in the 235U isotope.
- There are 7 electrons in the outermost shell (L) of an atom. Give its atomic number.
- Give the charge of the particle neutron.
- How many times a proton is heavier than the electron?
- What is the relation between nuclear charges and the atomic number?
- Deuterium is a naturally occurring isotope of which element?
- A beam of protons or electrons, which will be deflected more under an electric field?
- The atomic number of Aluminium is 13. Give the electron configuration of Al3+ ion.
- Mg and Mg2+, which one is more stable and which one has more electrons?
- An atom has 3 electrons in the M-shell (third shell). Mention the atomic number of the atom.
- Mention one of the natural spectrums.
Answer
- Nuclear force
- 20
- Protons and neutrons
- Hydrogen-1 (protium)
- Neutron
- 14
- 10
- M shell
- Nucleus
- 143
- 7
- Neutral
- 1836 times
- They are equal
- Hydrogen
- Electrons
- 2, 8
- Mg2+ is more stable and has fewer electrons
- 13
- 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:
- Both are isotopes of chlorine and have the same atomic number of 17.
- Both have the same number of electrons and the same electronic configuration.
Differences:
- 17Cl35 has 18 neutrons, while 17Cl37 has 20 neutrons.
- 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:
- Cations: positively charged ions formed by losing electrons.
- 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 |