Atomic Structure and Models

Which statement about covalent bonds is correct?

1. They are formed by the transfer of electrons.
2. They always involve the sharing of equal numbers of electrons.
3. They can be polar or nonpolar depending on the electronegativity difference.
4. They are stronger than ionic bonds in all cases.

Answer: (c) They can be polar or nonpolar depending on the electronegativity difference.

Which of the following models of the atom could best explain the observation that electrons occupy discrete energy levels?

1. Bohr’s model
2. Thomson’s model
3. Rutherford’s model
4. Alpha-particle model

Answer: (a) Bohr’s model

Neon has the electronic configuration 2, 8. It is chemically inert because:

1. It has a completely filled valence shell.
2. It has 8 protons in its nucleus.
3. Its electrons are arranged symmetrically.
4. It is a noble gas.

Answer: (a) It has a completely filled valence shell.

Bohr’s atomic model introduced the concept of discrete energy levels. A hydrogen atom’s electron transitions from the n = 3 energy level to n = 2, emitting a photon. Which statement correctly explains this observation?

1. The photon is absorbed as the electron moves to a higher energy level.
2. The energy of the photon equals the difference in energy between the two levels.
3. The electron moves closer to the nucleus, and the atom loses mass.
4. The photon emitted has the same energy as the ionisation energy of the atom.

Answer: (b) The energy of the photon equals the difference in energy between the two levels.

Which of the following statements correctly describe the characteristics of a neutral atom of any element?

1. In a neutral atom, the charge of the atom is one.
2. A neutral atom always has more electrons than neutrons.
3. In a neutral atom, the atomic number equals the number of protons.
4. A neutral atom always has equal numbers of protons and neutrons.

Answer: (c) In a neutral atom, the atomic number equals the number of protons.

Which of the following statements correctly describe the characteristics of the ion shown in the image?

1. It contains more protons than neutrons.
2. It contains more electrons than protons.
3. It contains more protons than electrons.
4. It contains more electrons than neutrons.

Answer: (b) It contains more electrons than protons.

Below is a table showing the isotopes of hydrogen. Based on the table, which of the following statements is correct? Isotope Protons Neutrons Electrons Protium 1 0 1 Deuterium 1 1 1 Tritium 1 2 1

1. All isotopes have different chemical properties due to varying neutron numbers
2. Tritium is the most abundant isotope of hydrogen.
3. Deuterium has two electrons in its outer shell.
4. The isotopes differ in mass numbers but have the same atomic number.

Answer: (d) The isotopes differ in mass numbers but have the same atomic number.

A compound has a molecular mass of 44 g/mol and consists of 27.3% carbon, 72.7% oxygen by mass. Reconstruct the molecular formula of the compound and identify its chemical nature.

1. CO; Carbon monoxide
2. C2O2; Dicarbon dioxide
3. CO2; Carbon dioxide
4. C2O; Dicarbon monoxide

Answer: (c) CO2; Carbon dioxide

J.J. Thomson conducted an experiment with a cathode ray tube and observed the deflection of rays in an electric field. He proposed the "plum pudding model" of the atom. Based on this model, consider the following scenario: If a positively charged plate is brought near the cathode rays, which of the following observations would align with Thomson's findings?

1. The rays are attracted toward the positively charged plate.
2. The rays are repelled by the positively charged plate.
3. The rays will split into two directions.
4. The rays will remain unaffected.

Answer: (a) The rays are attracted toward the positively charged plate.

An unknown element has an atomic number of 11. It reacts vigorously with water to produce a gas that burns with a ‘pop’ sound and forms a basic solution. What could be the electronic configuration and position of this element in the periodic table?

1. 2, 8, 1; Group 2, Period 3
2. 2, 8, 1; Group 1, Period 2
3. 2, 8, 1; Group 2, Period 2
4. 2, 8, 1; Group 1, Period 3

Answer: (d) 2, 8, 1; Group 1, Period 3