Lakhmir Singh & Manjit Kaur Test: Structure of the Atom - Class 9 MCQ

Answer:
The nucleus consists of protons and neutrons. Here is a detailed explanation of the components of the nucleus:
1. Protons:
- Protons are positively charged particles found in the nucleus of an atom.
- They have a mass of approximately 1 atomic mass unit (amu).
- The number of protons in an atom determines its atomic number, which defines the element.
2. Neutrons:
- Neutrons are neutral particles found in the nucleus of an atom.
- They have a mass similar to protons, approximately 1 amu.
- The number of neutrons in an atom can vary, resulting in different isotopes of an element.
3. Electrons:
- Electrons are negatively charged particles found in energy levels or shells outside the nucleus.
- They have a much smaller mass compared to protons and neutrons.
- The number of electrons in an atom is equal to the number of protons, ensuring overall neutrality.
Summary:
- The nucleus of an atom consists of protons and neutrons.
- Protons carry a positive charge and define the atomic number of an element.
- Neutrons are neutral particles and contribute to the mass of the atom.
- Electrons orbit around the nucleus in energy levels.

Valence Electrons in Sodium (Na)

• Sodium (Na) is a chemical element with atomic number 11.
• It belongs to group 1 of the periodic table, also known as the alkali metals group.
• The number of valence electrons in an atom is determined by its group number.
• Since sodium is in group 1, it has 1 valence electron.
• In the case of sodium, it readily loses its single valence electron to achieve a stable electron configuration, forming a Na+ ion.

The mass number, also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. It is approximately equal to the atomic mass of the atom expressed in atomic mass units.

Neutron is a fundamental particle which have–
There are four options given to choose from regarding the charge and mass of a neutron. Let's analyze each option to determine the correct answer.
Option A: 1 unit charge and 1 unit mass
- A neutron has no charge, so this option is incorrect.
Option B: No charge and 1 unit mass
- This option correctly states that a neutron has no charge. Neutrons are electrically neutral particles.
- Neutrons do have mass, with a mass of approximately 1 atomic mass unit (u) or 1.67 × 10^-27 kg.
- Therefore, option B is correct.
Option C: Have no charge and mass
- This option is incorrect as it implies that a neutron has no mass. However, neutrons do have mass.
Option D: Have –1 unit charge and 1 unit mass
- This option is incorrect as it states that a neutron has a negative charge. Neutrons are electrically neutral and do not possess any charge.
Therefore, the correct answer is option B: Neutrons have no charge and 1 unit mass.

The species that does not contain neutrons is option A: H (Hydrogen).
Explanation:
Hydrogen is the first element in the periodic table and has an atomic number of 1. It consists of only one proton in its nucleus and no neutrons. Neutrons are subatomic particles that have no charge and contribute to the mass of an atom.
Let's analyze the other options:
B: Li²
- Lithium (Li) is the element with atomic number 3.
- The superscript 2 indicates the charge, not the number of neutrons.
- The nucleus of lithium consists of 3 protons and a variable number of neutrons.
C: C
- Carbon (C) is the element with atomic number 6.
- It has 6 protons in its nucleus and a variable number of neutrons.
- Carbon has stable isotopes with 6, 7, and 8 neutrons.
D: O
- Oxygen (O) is the element with atomic number 8.
- It has 8 protons in its nucleus and a variable number of neutrons.
- Oxygen has stable isotopes with 8, 9, 10, 11, 12, 13, 14, 15, and 16 neutrons.
Therefore, among the given options, only Hydrogen (H) does not contain neutrons in its nucleus.

Explanation:
The mass number of an atom is equal to the number of nucleons. Nucleons are the particles found in the nucleus of an atom, which include protons and neutrons. Electrons are not included in the mass number because they have a negligible mass compared to protons and neutrons.
Key Points:
- The mass number of an atom is equal to the number of nucleons.
- Nucleons are the particles found in the nucleus of an atom.
- Nucleons include protons and neutrons.
- Electrons are not included in the mass number.
- Electrons have a negligible mass compared to protons and neutrons.

- The atomic number of an element is the number of protons in its nucleus.
- This defines the identity of the element and determines its position in the periodic table.
- Since protons have a positive charge, the atomic number is effectively the electrical charge of the nucleus.
- Electrons, which are negatively charged, balance this charge in a neutral atom.
- Therefore, the atomic number is best described as the electrical charge of the nucleus, making option C correct.

The lightest particle among the options given is the electron. Here is a detailed explanation:
Electron:
- The electron is a subatomic particle with a negative electric charge.
- It is considered to be one of the fundamental particles of matter.
- It is symbolized by the letter "e" and has a charge of -1.
- Electrons are found outside the atomic nucleus in orbitals or energy levels.
- They have a very small mass compared to protons and neutrons.
- The mass of an electron is approximately 9.10938356 × 10^-31 kilograms.
Neutron:
- The neutron is a subatomic particle with no electric charge.
- It is also considered to be one of the fundamental particles of matter.
- Neutrons are found inside the atomic nucleus along with protons.
- They have a mass slightly larger than that of protons.
- The mass of a neutron is approximately 1.674927471 × 10^-27 kilograms.
Proton:
- The proton is a subatomic particle with a positive electric charge.
- It is also considered to be one of the fundamental particles of matter.
- Protons are found inside the atomic nucleus along with neutrons.
- They have a mass slightly smaller than that of neutrons.
- The mass of a proton is approximately 1.672621898 × 10^-27 kilograms.
Conclusion:
- Among the options given, the electron is the lightest particle.
- It has a smaller mass compared to protons and neutrons.
- Therefore, the correct answer is B: Electron.

The correct option is C.
The nucleus of an atom is made up of protons and neutrons (two types of baryons) joined by the nuclear force. These baryons are further made up of sub-atomic fundamental particles known as quarks joined by the strong interaction.

The correct option is D.
The atomic size is of the order of 10⁻⁸
cm or 10⁻¹⁰ m or one angstrom unit.
On the other hand, the radius of an atomic nucleus is of the order of 10⁻¹³
cm or 10⁻¹⁵ m or one Fermi unit.

Isotopes are the atoms of the same element with similar atomic number but different atomic mass.The elements of isotopes share same chemical properties but different physical properties

According to the question, we need to determine the maximum number of electrons that can be accommodated in the nth level.

To solve this problem, we can use the formula for the maximum number of electrons in a specific energy level. The formula is given by:
Maximum number of electrons = 2n^2
Where:
- n represents the energy level or the principal quantum number.
Let's break down the solution into steps:
Step 1: Substitute the value of n into the formula.
- We are given the value of n as the nth level.
Step 2: Calculate the maximum number of electrons.
- Square the value of n (n^2).
- Multiply the squared value by 2 (2n^2).
Step 3: Determine the final answer.
- The maximum number of electrons that can be accommodated in the nth level is equal to the result obtained from step 2.
Therefore, the correct answer is option B: 2n^2.

Isotopes of an element are the atom which have:
- The same number of neutrons in their nuclei: Isotopes of an element have the same number of protons in their nuclei, which determines the element's atomic number. However, they can have different numbers of neutrons. This results in variations in their mass numbers.
- The same mass number: Isotopes have the same number of protons in their nuclei, which gives them the same atomic number. However, they have different numbers of neutrons, resulting in different mass numbers. Isotopes of an element have similar chemical properties due to the same number of electrons in their outer shells.
- Different number of electrons in their orbit: Isotopes have the same number of electrons in their orbit as they have the same atomic number. The number of electrons determines the element's chemical properties. Isotopes only differ in the number of neutrons in their nuclei.
- The same number of protons in their nuclei: Isotopes have the same number of protons in their nuclei, which determines the element's atomic number. However, they can have different numbers of neutrons, resulting in variations in their mass numbers.
Therefore, the correct answer is option D: The same number of protons in their nuclei.

Number of Electrons in Argon.

• Argon is a chemical element with the atomic number 18.
• As per the periodic table, the atomic number of an element represents the number of protons in the nucleus of an atom.
• Since atoms are electrically neutral, the number of electrons in an atom of Argon is also 18.

The correct option is D.
 Hydrogen is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one neutron, whereas the far more common protium has no neutrons in the nucleus.

Electrons in the valence shells of Sodium and Calcium:

Electronic configuration of Na is 2, 8, 1. Therefore, Na has 1 electron in its valence shell.

Electronic configuration of Ca is 2, 8, 8, 2. Therefore, Ca has 2 electrons in its valence shell.

 

To determine the maximum number of electrons that can be accommodated in the third shell (n = 3), we need to consider the following:
1. Maximum number of electrons in a shell:
The maximum number of electrons that can be accommodated in a shell is given by the formula 2n^2, where n is the principal quantum number.
2. Principal quantum number for the third shell:
In the case of the third shell (n = 3), the principal quantum number is 3.
3. Applying the formula:
Using the formula 2n^2, we can calculate the maximum number of electrons in the third shell as follows:
2(3^2) = 2(9) = 18
Therefore, the maximum number of electrons that can be accommodated in the third shell (n = 3) is 18.
Answer: C - 18

 

Both statements are correct. The first statement explains that an electron in a circular orbit undergoes acceleration due to its changing direction, which leads to the emission of energy. This is consistent with classical physics, where charged particles like electrons radiate energy when they are accelerated. The second statement accurately follows from the first: if an electron loses energy as it radiates, it would indeed spiral inward and eventually fall into the nucleus, resulting in atomic instability. However, empirical evidence shows that atoms are stable, which implies that the classical model of the atom is insufficient and that quantum mechanics provides a more accurate description of atomic structure, where electrons occupy defined energy levels that prevent them from spiraling into the nucleus.

 

Rutherford aimed to understand the arrangement of electrons within the atom through his experiments with alpha particles.

Thomson compared his model of the atom to a Christmas pudding, where the positive charge is the pudding itself and the electrons are the currants embedded within it.