Which sub-atomic particle was discovered by E. Goldstein?

Correct Option: B. Solution: E. Goldstein discovered the proton.

Structure of the Atom

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CBSE Learning Objectives – Key Concepts & Skills You Must Know

Understand the historical development of atomic models.
Explain Rutherford's alpha-particle scattering experiment and its significance.
Describe Bohr's model of the atom and its improvements over previous models.
Identify the three sub-atomic particles: electrons, protons, and neutrons.
Define atomic number and mass number, and explain their significance in identifying elements.
Differentiate between isotopes and isobars with examples.
Calculate the average atomic mass of an element based on isotopic composition.
Explain the concept of valency and its determination for various elements.

CBSE Revision Notes & Quick Summary for Last-Minute Study

Structure of the Atom

Atomic Models

Thomson's Model of the Atom

Proposed that an atom consists of a positively charged sphere with electrons embedded in it, similar to a Christmas pudding.
Electrons are like currants in the pudding, evenly distributed throughout the positive charge.

Rutherford's Model of the Atom

Conducted an experiment using alpha particles to probe the structure of the atom.
Proposed that a tiny nucleus exists at the center of the atom with electrons revolving around it.

Bohr's Model of the Atom

Introduced the concept of discrete orbits for electrons around the nucleus.
Electrons do not radiate energy while revolving in these orbits.

Subatomic Particles

Electrons: Negatively charged particles.
Protons: Positively charged particles found in the nucleus.
Neutrons: Neutral particles also found in the nucleus.

Atomic Number and Mass Number

Atomic Number (Z): Number of protons in the nucleus.
Mass Number (A): Total number of protons and neutrons in the nucleus.

Isotopes and Isobars

Isotopes: Atoms of the same element with different mass numbers (e.g., Carbon-12 and Carbon-14).
Isobars: Atoms with the same mass number but different atomic numbers (e.g., Calcium and Argon both with mass number 40).

Valency

Valency is the combining capacity of an atom, determined by the number of electrons in the outermost shell.
Example: Sodium (Na) has a valency of 1, while Oxygen (O) has a valency of 2.

Electron Configuration

Electrons are arranged in shells around the nucleus:
- K shell (n=1): Max 2 electrons
- L shell (n=2): Max 8 electrons
- M shell (n=3): Max 18 electrons
- N shell (n=4): Max 32 electrons

Applications of Isotopes

Isotopes have various applications:
- Uranium isotope used as fuel in nuclear reactors.
- Cobalt isotope used in cancer treatment.
- Iodine isotope used in the treatment of goitre.

Important Diagrams

Bohr Model: Shows electron arrangements in concentric circles around the nucleus.
Atomic Structure Diagram: Illustrates the nucleus and electron shells, labeling K, L, M, and N shells.

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes and Exam Tips

Common Pitfalls

Misunderstanding Isotopes and Isobars: Students often confuse isotopes (same atomic number, different mass numbers) with isobars (same mass number, different atomic numbers).
Incorrect Electronic Configuration: Ensure the electronic configuration follows the correct order of filling (K, L, M, N shells).
Valency Calculation Errors: Students may miscalculate valency by not considering the number of electrons in the outermost shell correctly.

Tips for Success

Review Atomic Models: Familiarize yourself with Thomson's, Rutherford's, and Bohr's models to understand the evolution of atomic theory.
Practice Calculating Average Atomic Mass: Work on problems involving the calculation of average atomic mass from isotopic abundances.
Understand the Concept of Atomic Number and Mass Number: Remember that atomic number (Z) is the number of protons, while mass number (A) is the sum of protons and neutrons.
Use Tables for Reference: Utilize tables for quick reference on atomic numbers, mass numbers, and valencies of elements.

CBSE Quiz & Practice Test – MCQs, True/False Questions with Solutions

Multiple Choice Questions

79.9 u

80.0 u

80.1 u

80.2 u

Correct Answer: C

Solution:

The average atomic mass is calculated as (79 u * 0.497) + (81 u * 0.503) = 80.1 u.

Correct Answer: B

Solution:

Magnesium has two electrons in its outermost shell, giving it a valency of 2.

10.4 u

10.6 u

10.8 u

11.0 u

Correct Answer: B

Solution:

The average atomic mass is calculated as follows:

\text{Average atomic mass} = (10 \times 0.6) + (11 \times 0.4) = 6 + 4.4 = 10.6 \text{ u}

Isotopes have the same atomic number but different mass numbers.

Isotopes have different atomic numbers and different mass numbers.

Isotopes have the same mass number but different atomic numbers.

Isotopes have different chemical properties.

Correct Answer: A

Solution:

Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to a different number of neutrons. This is why option A is correct.

Correct Answer: C

Solution:

The K shell can hold a maximum of 2 electrons and the L shell can hold a maximum of 8 electrons. Therefore, the total number of electrons is

2 + 8 = 10

Iodine-127

Iodine-129

Iodine-131

Iodine-135

Correct Answer: C

Solution:

Iodine-131 is commonly used in the treatment of goitre.

Isotopes have the same number of neutrons but different numbers of protons.

Isotopes have the same atomic number but different mass numbers.

Isotopes have different chemical properties.

Isotopes are atoms of different elements with the same mass number.

Correct Answer: B

Solution:

Isotopes are defined as atoms of the same element having the same atomic number but different mass numbers due to varying numbers of neutrons.

Uranium

Cobalt

Iodine

Chlorine

Correct Answer: B

Solution:

An isotope of cobalt is used in the treatment of cancer.

Nitrogen

Carbon

Oxygen

Helium

Correct Answer: B

Solution:

Carbon has an atomic number of 6, which means it has 6 protons in its nucleus.

Most alpha particles passed through the foil without deflection.

Some alpha particles were deflected at large angles.

Alpha particles were absorbed by the foil.

Alpha particles were deflected at small angles.

Correct Answer: B

Solution:

The large-angle deflections of alpha particles indicated the presence of a dense, positively charged nucleus that repelled the positively charged alpha particles.

Isotopes have different chemical properties.

Isotopes have different atomic numbers.

Isotopes have the same number of protons but different mass numbers.

Isotopes have the same mass number but different numbers of neutrons.

Correct Answer: C

Solution:

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons, leading to different mass numbers.

Isobars have the same atomic number but different mass numbers.

Isobars have the same mass number but different atomic numbers.

Isobars have the same number of neutrons but different atomic numbers.

Isobars have the same chemical properties.

Correct Answer: B

Solution:

Isobars are atoms with the same mass number but different atomic numbers.

Most alpha particles passed through the foil without deflection.

Some alpha particles were deflected at small angles.

A few alpha particles were deflected back at large angles.

Alpha particles were absorbed by the foil.

Correct Answer: C

Solution:

The observation that a few alpha particles were deflected back at large angles indicated that they encountered a very small, dense, positively charged nucleus.

Correct Answer: B

Solution:

The element with atomic number 8 is oxygen, which has 6 electrons in its outermost shell and needs 2 more to complete its octet, giving it a valency of 2.

It has 8 protons and 6 neutrons.

It has 6 protons and 8 neutrons.

It has 14 protons and 6 neutrons.

It has 6 protons and 14 neutrons.

Correct Answer: B

Solution:

The atomic number indicates the number of protons, which is 6. The mass number is the sum of protons and neutrons, so there are 8 neutrons (14 - 6 = 8).

Helium

Neon

Lithium

Oxygen

Correct Answer: B

Solution:

Neon has a complete outermost shell with 8 electrons, making it a noble gas.

Rutherford's model

Bohr's model

Thomson's model

Chadwick's model

Correct Answer: C

Solution:

Thomson's model of the atom proposed that electrons are embedded in a positively charged sphere, similar to a plum pudding.

Atoms with the same number of protons but different number of neutrons.

Atoms with the same number of neutrons but different number of protons.

Atoms with the same mass number but different atomic numbers.

Atoms with the same chemical properties but different physical properties.

Correct Answer: C

Solution:

Isobars are atoms that have the same mass number but different atomic numbers, meaning they have the same total number of nucleons but differ in the number of protons and neutrons.

Helium (He)

Magnesium (Mg)

Fluorine (F)

Oxygen (O)

Correct Answer: B

Solution:

Magnesium (Mg) has the electronic configuration of 2, 8, 2. It can lose two electrons to achieve a stable electronic configuration, forming a +2 ion. Therefore, option B is correct.

Correct Answer: B

Solution:

The atomic number is equal to the number of protons in an atom. Therefore, it is 11.

Correct Answer: D

Solution:

The mass number of an atom is the sum of protons and neutrons. Therefore, 6 protons + 8 neutrons = 14.

U-235

U-238

U-234

U-236

Correct Answer: A

Solution:

U-235 is the isotope of uranium used as fuel in nuclear reactors due to its ability to sustain a chain reaction.

Correct Answer: C

Solution:

The mass number is the sum of protons and neutrons in the nucleus, which is 6 + 8 = 14.

Correct Answer: C

Solution:

The mass number is the sum of protons and neutrons. Therefore, mass number = 3 (protons) + 4 (neutrons) = 7.

Correct Answer: A

Solution:

The atom initially has 15 protons and 15 electrons. Losing 3 electrons results in 15 protons and 12 electrons, giving a net charge of

15 - 12 = 3+

Neon

Oxygen

Sodium

Chlorine

Correct Answer: A

Solution:

Neon has a completely filled outermost shell with 8 electrons in the L shell, making it stable and inert.

J.J. Thomson

E. Goldstein

Ernest Rutherford

Niels Bohr

Correct Answer: A

Solution:

J.J. Thomson is credited with the discovery of the electron.

1:1

3:1

1:3

2:1

Correct Answer: B

Solution:

The average atomic mass is closer to 35, suggesting that the isotope with mass 35 is more abundant. A 3:1 ratio of the isotopes with masses 35 and 37 would yield an average mass of 35.5 u.

Correct Answer: B

Solution:

The number of neutrons in an atom is given by the difference between the mass number and the atomic number. For this atom, the number of neutrons is 16 - 8 = 8. Therefore, option B is correct.

Neon

Sodium

Oxygen

Fluorine

Correct Answer: A

Solution:

Neon has a complete octet with 8 electrons in its outermost shell, making it a noble gas.

Electron

Proton

Atomic nucleus

Neutron

Correct Answer: C

Solution:

Rutherford's experiment demonstrated that the atom has a small, dense, positively charged nucleus, leading to the discovery of the atomic nucleus. Thus, option C is correct.

Neutron

Proton

Positron

Anti-proton

Correct Answer: D

Solution:

The particle 'Q' has a mass similar to a proton but with an opposite charge, indicating it is an anti-proton.

Isotopes are atoms of the same element with different atomic numbers.

Isotopes are atoms of different elements with the same mass number.

Isotopes are atoms of the same element with different mass numbers.

Isotopes are atoms of different elements with the same atomic number.

Correct Answer: C

Solution:

Isotopes are defined as atoms of the same element that have the same atomic number but different mass numbers due to a different number of neutrons.

Helium

Deuterium

Neutronium

A neutron

Correct Answer: D

Solution:

Replacing a proton with a neutron in a hydrogen atom results in a lone neutron, as the atomic number becomes zero, which does not correspond to any element.

Electron

Proton

Neutron

Photon

Correct Answer: B

Solution:

E. Goldstein discovered the proton.

Isotopes have the same atomic number but different mass numbers.

Isotopes have different atomic numbers and different mass numbers.

Isotopes have the same mass number but different atomic numbers.

Isotopes have different chemical properties.

Correct Answer: A

Solution:

Isotopes are atoms of the same element with the same atomic number but different mass numbers.

100.5 u

101.0 u

100.0 u

101.5 u

Correct Answer: A

Solution:

The average atomic mass is calculated as:

\text{Average atomic mass} = (100 \times 0.75) + (102 \times 0.25) = 75 + 25.5 = 100.5\, \text{u}

Boron

Carbon

Oxygen

Neon

Correct Answer: A

Solution:

Boron has three electrons in its outermost shell, giving it a valency of 3.

Thomson's Model

Rutherford's Model

Bohr's Model

Quantum Mechanical Model

Correct Answer: B

Solution:

Rutherford's model proposed that electrons revolve around a central nucleus, which was a significant departure from Thomson's model.

Correct Answer: C

Solution:

The element with atomic number 6 is carbon, which has an electron configuration of 1s² 2s² 2p². It needs 4 more electrons to complete its octet, so its valency is 4.

1s² 2s² 2p⁶ 3s² 3p³

1s² 2s² 2p⁶ 3s² 3p⁶

1s² 2s² 2p⁶ 3s² 3p⁴

1s² 2s² 2p⁶ 3s¹ 3p⁶

Correct Answer: B

Solution:

The atom has 15 protons and 15 electrons in its neutral state, with the configuration 1s² 2s² 2p⁶ 3s² 3p³. Losing three electrons results in a configuration of 1s² 2s² 2p⁶ 3s² 3p⁶.

Correct Answer: C

Solution:

According to the formula

2n^2

, where

n

is the shell number, the M shell (n=3) can hold a maximum of

2 \times 3^2 = 18

electrons.

Correct Answer: B

Solution:

The atomic number of an element is equal to the number of protons in its nucleus. Therefore, an atomic number of 8 means it has 8 protons.

Correct Answer: B

Solution:

Oxygen, with an atomic number of 8, has a valency of 2 because it needs two more electrons to complete its outer shell.

Lithium

Neon

Sodium

Aluminium

Correct Answer: C

Solution:

Sodium (Na) has an electronic configuration of 2, 8, 1. When it loses one electron to form Na⁺, the outermost shell becomes filled with 8 electrons.

35.5 u

36 u

34.5 u

37 u

Correct Answer: A

Solution:

The average atomic mass of chlorine is 35.5 u, based on the isotopic masses and their ratio.

Correct Answer: B

Solution:

The number of neutrons is calculated by subtracting the atomic number from the mass number:

31 - 15 = 16

Proton

Neutron

Electron

Photon

Correct Answer: C

Solution:

J.J. Thomson is credited with the discovery of the electron, a negatively charged subatomic particle.

Most alpha particles passed through the foil without deflection.

Alpha particles were absorbed by the gold foil.

All alpha particles were deflected at large angles.

Alpha particles emitted light upon hitting the foil.

Correct Answer: A

Solution:

Rutherford observed that most alpha particles passed through the gold foil without deflection, indicating that most of the atom is empty space, with a small, dense, positively charged nucleus at the center.

Helium

Oxygen

Sodium

Chlorine

Correct Answer: B

Solution:

Oxygen has 6 electrons in its outermost shell and needs 2 more to complete an octet, giving it a valency of 2.

Electron

Proton

Neutron

Alpha particle

Correct Answer: A

Solution:

The mass of an electron is about 1/2000th the mass of a proton.

Rutherford's model

Bohr's model

Thomson's model

Quantum mechanical model

Correct Answer: C

Solution:

Thomson's model of the atom, also known as the 'plum pudding model,' proposed that electrons are embedded within a positively charged sphere.

-1

Correct Answer: C

Solution:

A proton has a charge of +1.

Correct Answer: A

Solution:

The K shell can hold a maximum of 2 electrons and the L shell can hold a maximum of 8 electrons. Therefore, if both K and L shells are completely filled, the total number of electrons is 2 + 8 = 10.

Uranium-235

Iodine-131

Cobalt-60

Carbon-14

Correct Answer: C

Solution:

Cobalt-60 is an isotope used in radiotherapy for the treatment of cancer due to its radioactive properties.

Correct Answer: A

Solution:

The conservation of nucleons requires that the sum of mass numbers and atomic numbers before and after the reaction remains constant. Given the fission products and neutrons, the atomic number of 'Z' must be 92.

20%

40%

60%

80%

Correct Answer: A

Solution:

Let the abundance of the isotope with mass 22 be

x

. Then,

20(1-x) + 22x = 20.4

. Solving gives

20 - 20x + 22x = 20.4

2x = 0.4

x = 0.2

or 20%.

Proton

Electron

Neutron

Alpha particle

Correct Answer: B

Solution:

J.J. Thomson is credited with the discovery of the electron, a sub-atomic particle with a negative charge.

Electron

Proton

Neutron

Positron

Correct Answer: B

Solution:

E. Goldstein discovered canal rays, which led to the discovery of protons, a positively charged subatomic particle.

Protons were discovered by J.J. Thomson using cathode ray tubes.

Protons were discovered by E. Goldstein through canal rays.

Protons were discovered by Rutherford using alpha-particle scattering.

Protons were discovered by Niels Bohr through spectral lines.

Correct Answer: B

Solution:

E. Goldstein discovered the presence of positively charged particles, later identified as protons, through his experiments with canal rays.

True or False

Correct Answer: False

Solution:

The mass number of an atom is equal to the total number of protons and neutrons in its nucleus.

Correct Answer: False

Solution:

It was J.J. Thomson's model that proposed electrons are embedded in a positively charged sphere, not Rutherford's model.

Correct Answer: True

Solution:

Isotopes have the same chemical properties because they have the same number of electrons, but different physical properties due to different masses.

Correct Answer: False

Solution:

The valency of an element is determined by the number of electrons in its outermost shell, not by the number of protons in the nucleus.

Correct Answer: False

Solution:

Isobars are atoms of different elements that have the same mass number but different atomic numbers, not the same atomic number.

Correct Answer: True

Solution:

J.J. Thomson proposed the 'plum pudding' model of the atom, where electrons are embedded in a positively charged sphere, similar to seeds in a watermelon.

Correct Answer: False

Solution:

The mass of an electron is about 1/2000th the mass of a proton, not 2000 times greater.

Correct Answer: True

Solution:

J.J. Thomson's model of the atom suggested that electrons are embedded within a positively charged sphere.

Correct Answer: False

Solution:

Rutherford's experiment led to the discovery of the atomic nucleus, not the electron.

Correct Answer: False

Solution:

Isotopes of an element have the same chemical properties but different physical properties.

Correct Answer: False

Solution:

Atoms are divisible and contain sub-atomic particles such as electrons, protons, and neutrons.

Correct Answer: True

Solution:

The mass of a proton is approximately 2000 times that of an electron, as stated in the text.

Correct Answer: True

Solution:

An isotope of uranium is indeed used as a fuel in nuclear reactors, as mentioned in the excerpts.

Correct Answer: False

Solution:

The atomic number of an element is the same as the number of protons in its nucleus, not neutrons.

Correct Answer: False

Solution:

J.J. Thomson discovered the electron but it was Dalton who originally proposed that atoms are indivisible. Thomson's work showed that atoms have internal structure, contradicting Dalton's idea.

Correct Answer: True

Solution:

The atomic number is indeed defined as the number of protons in the nucleus of an atom.

Correct Answer: True

Solution:

Rutherford's model proposed a tiny nucleus with electrons revolving around it, but it could not explain why the electrons did not spiral into the nucleus, leading to instability.

Correct Answer: False

Solution:

Rutherford's alpha-particle scattering experiment led to the discovery of the atomic nucleus, not the electron.

Correct Answer: True

Solution:

Rutherford's model proposed a tiny nucleus with electrons revolving around it, but it could not explain the stability of the atom.

Correct Answer: False

Solution:

Isobars are atoms of different elements with the same mass number but different atomic numbers.

Correct Answer: True

Solution:

Isotopes are defined as atoms of the same element that have the same number of protons (atomic number) but different numbers of neutrons, resulting in different mass numbers.

Correct Answer: False

Solution:

The atomic number of an element is determined by the number of protons in its nucleus, not neutrons.

Correct Answer: True

Solution:

Atoms are composed of protons and electrons, which mutually balance their charges. Protons are positively charged, and electrons are negatively charged.

Correct Answer: True

Solution:

Bohr's model proposed that electrons occupy specific energy levels or shells around the nucleus, which explained the stability of atoms better than previous models.

Structure of the Atom

AI Learning Assistant

CBSE Learning Objectives – Key Concepts & Skills You Must Know

CBSE Revision Notes & Quick Summary for Last-Minute Study

Structure of the Atom

Atomic Models

Thomson's Model of the Atom

Rutherford's Model of the Atom

Bohr's Model of the Atom

Subatomic Particles

Atomic Number and Mass Number

Isotopes and Isobars

Valency

Electron Configuration

Applications of Isotopes

Important Diagrams

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes and Exam Tips

Common Pitfalls

Tips for Success

Multiple Choice Questions

Q1.What is the average atomic mass of bromine if it consists of isotopes 79 Br (49.7%) and 81 Br (50.3%)?

Correct Answer: C

Q2.What is the valency of magnesium based on its electronic configuration?

Correct Answer: B

Q3.Consider an element with two isotopes: Isotope A has a mass of 10 u and an abundance of 60%, while Isotope B has a mass of 11 u and an abundance of 40%. What is the average atomic mass of this element?

Correct Answer: B

Q4.In the context of atomic structure, which of the following statements about isotopes is correct?

Correct Answer: A

Q5.If an atom has its K and L shells completely filled, what is the total number of electrons in the atom?

Correct Answer: C

Q6.Which isotope of iodine is used in the treatment of goitre?

Correct Answer: C

Q7.Which of the following statements is true regarding isotopes?

Correct Answer: B

Q8.Which of the following isotopes is used in the treatment of cancer?

Correct Answer: B

Q9.Which element has an atomic number of 6?

Correct Answer: B

Q10.In Rutherford's gold foil experiment, which of the following observations led to the conclusion that the nucleus is positively charged?

Correct Answer: B

Q11.Which of the following statements about isotopes is correct?

Correct Answer: C

Q12.Which of the following statements is true about isobars?

Correct Answer: B

Q13.In Rutherford's gold foil experiment, which observation led to the conclusion that the nucleus is very small and dense?

Correct Answer: C

Q14.What is the valency of an element with an atomic number of 8?

Correct Answer: B

Q15.An isotope of an element has a mass number of 14 and an atomic number of 6. Which of the following statements is true about this isotope?

Correct Answer: B

Q16.Which of the following elements has a complete outermost shell with 8 electrons?

Correct Answer: B

Q17.Which model of the atom proposed that electrons are embedded in a positively charged sphere?

Correct Answer: C

Q18.Which of the following best describes the concept of isobars?

Correct Answer: C

Q19.Which of the following elements is most likely to form an ion with a +2 charge based on its electronic configuration?

Correct Answer: B

Q20.What is the atomic number of an element with 11 protons?

Correct Answer: B

Q21.If an atom has 6 protons and 8 neutrons, what is its mass number?

Correct Answer: D

Q22.Which isotope of uranium is commonly used as a fuel in nuclear reactors?

Correct Answer: A

Q23.What is the mass number of an atom with 6 protons and 8 neutrons?

Correct Answer: C

Q24.If an atom has 3 protons, 4 neutrons, and 3 electrons, what is its mass number?

Correct Answer: C

Q25.Consider an atom with atomic number 15 and mass number 31. If this atom forms an ion by losing 3 electrons, what will be the charge on the ion?

Correct Answer: A

Q26.Which of the following elements has a completely filled outermost shell in its neutral atomic state?

Correct Answer: A

Q27.Which scientist is credited with the discovery of the electron?

Correct Answer: A

Q28.If an element has isotopes with mass numbers 35 and 37, and the average atomic mass is 35.5 u, what is the approximate ratio of these isotopes in nature?

Correct Answer: B

Q29.If an atom has an atomic number of 8 and a mass number of 16, how many neutrons does it have?

Correct Answer: B

Q30.Which of the following elements has a complete octet in its outermost shell?