1. 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
Explanation: 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.
2. When an electron shifts to an inner shell, it:
a) Absorbs photon
b) Emits a photon
c) Emits a positron
d) Absorbs a positron
Explanation: 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.
3. 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
Explanation: Neutrons were not discovered by then. Rutherford only suggested that the nucleus has a positive charge, but did not comment on its structure.
4. 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
Explanation: 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.
5. 4f orbital has higher energy than 5p.
a) True
b) False
Explanation: 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.
6. Which of the following orbitals do not exist?
a) 3p
b) 4s
c) 2s
d) 3f
Explanation: 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.
7. Elements in the same column of the periodic table have:
a) Similar valence shell electron configuration
b) Same value of highest principal quantum number
c) Same number of nucleons
d) All of the mentioned
Explanation: The elements having similar valence shell electrons have similar chemical properties like reactivity, nature of bonds in their molecules etc. Hence in the modern periodic table, they were grouped in vertical columns called ‘groups’.
8. As we move down a group, electronegativity of elements generally:
a) Increases
b) Decreases
c) Increases and then decreases
d) Decreases and then increases
Explanation: As we move down a group, atomic size increases which means that the valence electrons are much farther from the nucleus and hence experience less force of attraction. Hence the electronegativity decreases down the group.
9. How many periods are there in a modern periodic table?
a) 5
b) 6
c) 7
d) 8
Explanation: Modern periodic table places elements having the same maximum principal quantum number in one period. There are seven periods, though the seventh period consists of many unstable artificial elements.
10. Temporary IUPAC systematic symbol for the synthetic element 117 is:
a) Uuh
b) Uns
c) Uus
d) Une
Explanation: IUPAC has assigned temporary systematic name Ununseptium [=Un(1) +un(1) + sept(7) + ium] to the element with atomic number 117. It belongs to group 17 of the periodic table and is predicted to be a halogen. As of 2015, its discovery has not been officially confirmed.