Solved Practice Questions on Atomic Models | Physical Chemistry PDF Download

Q.1. In the wave-mechanical model of an atom, degenerate energy levels have:
(a) Equal energy
(b) Equal number of electrons
(c) Same shape
(d) Electrons with the same spin

Correct Answer is Option (a)
Degenerate energy levels have equal energy. In an atom, the orbitals in the same subshell are degenerate in absence of an external magnetic field. 

Q.2. According to Dalton’s Atomic Theory, matter consists of indivisible _______
(a) Molecules
(b) Atoms
(c) Ions
(d) Mixtures

Correct Answer is Option (b)
Atom is the basic unit of life. A molecule is a compound made up of 2 or more atoms held by chemical bonds. The mixture is a combination of pure substances in a ratio. Ion is either positively or negatively charged. 

Q.3. Paired electrons in an atom have equal values of all of the four quantum numbers.
(a) True
(b) False

Correct Answer is Option (b)
According to Pauli’s exclusion principle, no two electrons in an atom can have all four quantum numbers equal. Paired electrons have opposite spins. 

Q.4. Atoms of different elements differ in mass.
(a) True
(b) False

Correct Answer is Option (a)
Each and every element has a different mass. For example, carbon’s molecular weight is 12.0107 u, oxygen’s molecular weight is 15.999 u and nitrogen’s molecular weight is 14.0067 u. Hence it’s different for different elements. 

Q.5. Protons attract electrons. Then why do electrons not fall on the nucleus?
(a) Neutrons repel the electrons
(b) Electrons in ground state cannot radiate energy
(c) At very small distances, protons repel electrons
(d) Inner electrons repel those in outer orbitals

Correct Answer is Option (b)
In the ground state, electrons form standing waves. Standing waves are those in which energy is not transferred. Hence, electrons are bound to revolve around the nucleus with constant potential energy. 

Q.6. What did Dalton’s Theory couldn’t explain?
(a) gaseous volumes
(b) conservation of mass
(c) chemical philosophy
(d) indivisible atoms

Correct Answer is Option (a)
Dalton’s atomic theory couldn’t explain gaseous volumes, because as per his view, different elements have different mass but this isn’t true. This is explained by Gay lussac’s law. This is one of the major limitations of Dalton’s atomic theory. 

Q.7. Number of atomic orbitals in nth shell is:
(a) n² 
(b) 2n² 
(c) 2n + 1
(d) n − 1

Correct Answer is Option (a)
Every shell contains n² orbitals and every orbital can accommodate a maximum of 2 electrons. Hence a maximum of 2n² electrons can reside in nth shell. 

Q.8. What is the name of Dalton’s publication?
(a) A New system of atomic Philosophy
(b) An old system of Chemical Philosophy
(c) A New System of Chemical Philosophy
(d) A New System of Chemical Prophecy

Correct Answer is Option (c)
Dalton published ” A New System of Chemical Philosophy” in 1808. He proposed a theory in that, that is Dalton’s atomic theory. It also has some limitations like it couldn’t explain how molecules combine i.e. their driving force. 

Q.9. Electronic configuration of Cu is [Ar] 3d10 4s1. Which rule is violated in this configuration?
(a) Aufbau Principle
(b) Hund’s Rule of Maximum Multiplicity
(c) Pauli’s Exclusion Principle
(d) None of the mentioned

Correct Answer is Option (a)
According to the Aufbau principle, orbitals of lower energy are completely filled before electrons start occupying higher energy orbitals. But in copper, higher energy 3d is filled before lower energy 4s. Such violation of the Aufbau principle appears in about 20 elements. 

Q.10. Which of the following may not be explained by Dalton’s atomic theory?
(a) reason for combining atoms
(b) conservation of mass
(c) chemical philosophy
(d) indivisible atoms

Correct Answer is Option (a)
Dalton’s atomic theory couldn’t explain the reason for combining atoms. This is one of the major limitations of Dalton’s atomic theory. Though it could explain the conservation of mass, indivisible atoms and definite proportions. 

Q.11. Law of conservation of mass isn’t explained in Dalton’s atomic theory.
(a) True
(b) False

Correct Answer is Option (b)
Law of conservation of mass is explained in Dalton’s atomic theory. He said that reorganization of atoms is involved in chemical reactions. This means mass is neither created nor destroyed in a chemical reaction i.e. explained. 

Q.12. When an electron shifts to an inner shell, it:
(a) Absorbs photon
(b) Emits a photon
(c) Emits a positron
(d) Absorbs a positron

Correct Answer is Option (b)
Generally, lower potential energy means more stability. Excited electrons lose energy in the form of photons to shift to stable empty inner shells. Positron is anti-particle of an electron. 

Q.13. What is 1 Dalton?
(a) a unified mass unit, 1.360539040(20) × 10⁻²⁷kg
(b) a unified mass unit, 1.640539040(20) × 10⁻²⁷kg
(c) a unified mass unit, 1.660539040(20) × 10⁻²⁷kg
(d) a unified mass unit, 1.660539040(20) × 10⁻²⁷kg

Correct Answer is Option (d)
Dalton is also known as the unified mass unit that is equal to 1.660539040(20) × 10⁻²⁷kg or 931.4940954(57)MeV/c² or 1822.888486192(53)m_e (symbol: u, or Da or AMU). It’s a standard unit of mass on the molecular and atomic scale. 

Q.14. Around 1911, Rutherford suggested a planetary model of atomic structure. Which of the following was not a proposition of this model?
(a) Electrons revolve in circular orbits around the nucleus
(b) Nucleus consists of protons and neutrons
(c) Mass of atom is concentrated in the nucleus
(d) Most of the volume in an atom is void

Correct Answer is Option (b)
Neutrons were not discovered by then. Rutherford only suggested that the nucleus has a positive charge, but did not comment on its structure. 

Q.15. Could Dalton’s atomic theory explain the laws of chemical combinations?
(a) No
(b) Yes
(c) Only a few
(d) Except one

Correct Answer is Option (b)
Yes, it could explain all the laws of chemical combinations i.e. Law of Conservation of Mass, Law of Definite Proportions, Law of Multiple Proportions, Gay Lussac’s Law of Gaseous Volumes, and Avogadro’s Law. 

Q.16. Which of the Bohr’s postulates was incorrect?
(a) Energy of electrons is quantized
(b) Momentum of electrons is quantized
(c) Electrons release energy when shifting from excited state to ground state
(d) Electrons revolve around the nucleus in fixed circular orbits

Correct Answer is Option (d)
Heisenberg uncertainty principle implies that exact position and momentum of electrons cannot be known with certainty and hence, definite circular paths are not feasible. Certain regions around the nucleus (called orbitals) have a high probability of the existence of electrons. 

Q.17. They are no limitations to Dalton’s atomic theory.
(a) True
(b) False

Correct Answer is Option (b)
There are limitations to Dalton’s atomic theory. Dalton’s atomic theory couldn’t explain the reason for combining atoms. He also couldn’t explain gaseous volumes, because as per his view, different elements have different mass but this isn’t true. This is explained by Gay lussac’s law. 

Q.18. 4f orbital has higher energy than 5p.
(a) True
(b) False

Correct Answer is Option (a)
Sum of principal and azimuthal quantum numbers for 4f is (4 + 3 =) 7 and that for 5p is (5 + 1 =) 6. As a general rule, higher the sum, higher is the energy. 

Q.19. All atoms of a given element have identical ______ including identical ______
(a) Properties, mass
(b) Weight, volume
(c) Volume, properties
(d) Temperature, pressure

Correct Answer is Option (a)
According to Dalton’s Atomic Theory, All atoms of a given element have identical properties, including identical mass. The reason behind this is that they belong to the same element (here “they” is about atoms). 

Q.20. Which of the following orbitals do not exist?
(a) 3p
(b) 4s
(c) 2s
(d) 3f

Correct Answer is Option (d)
For principal quantum number 3, only possible values of azimuthal quantum number are 0, 1, and 2. Azimuthal quantum number of an f-orbital is 3.