Chemistry MCQs for NEET — Practice Questions with Answers

The text explicitly states: 'unlike orbitals of hydrogen or hydrogen like species, whose energies depend only on the quantum number n, the energies of the orbitals in multi-electron atoms depend on quantum numbers n and l.' (Reference: 'the energies of the orbitals in multi-electron atoms depend on quantum numbers n and l.')

The Aufbau principle states: 'in the ground state of the atoms, the orbitals are filled in order of their increasing energies. In other words, electrons first occupy the lowest energy orbital available to them and enter into higher energy orbitals only after the lower energy orbitals are filled.' (Reference: 'Aufbau Principle: The principle states : in the ground state of the atoms, the orbitals are filled in order of their increasing energies.')

The text states: 'The restriction imposed by Pauli’s exclusion principle on the number of electrons in an orbital helps in calculating the capacity of electrons to be present in any subshell. For example, subshell 1s comprises one orbital and thus the maximum number of electrons present in 1s subshell can be two, in p and d subshells, the maximum number of electrons can be 6 and 10 and so on. This can be summed up as : the maximum number of electrons in the shell with principal quantum number n is equal to $2n^2$.' (Reference: 'the maximum number of electrons in the shell with principal quantum number n is equal to $2n^2$.')

The text provides the useful order of filling: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p... It specifically states: 'For example, valence electron in potassium must choose between 3d and 4s orbitals and as predicted by this sequence, it is found in 4s orbital.' (Reference: 'For example, valence electron in potassium must choose between 3d and 4s orbitals and as predicted by this sequence, it is found in 4s orbital.')

The context on molecular orbitals states: 'The bonding molecular orbital has lower energy and hence greater stability than the corresponding antibonding molecular orbital.' (Reference: 'The bonding molecular orbital has lower energy and hence greater stability than the corresponding antibonding molecular orbital.')

The context states: 'energies of the orbitals in the same subshell decrease with increase in the atomic number (Zeff). For example, energy of 2s orbital of hydrogen atom is greater than that of 2s orbital of lithium and that of lithium is greater than that of sodium and so on, that is, $E_{2s(H)} > E_{2s(Li)} > E_{2s(Na)} > E_{2s(K)}$.' Therefore, the correct order is $E_{2s(H)} > E_{2s(Li)} > E_{2s(Na)}$. (Reference: '$E_{2s(H)} > E_{2s(Li)} > E_{2s(Na)} > E_{2s(K)}$')

The text mentions: 'It may be noted that different subshells of a particular shell have different energies in case of multi-electrons atoms. However, in hydrogen atom, these have the same energy.' (Reference: 'However, in hydrogen atom, these have the same energy.')

The context states: 'if two orbitals have the same value of (n + l), the orbital with lower value of n will have the lower energy.' (Reference: 'if two orbitals have the same value of (n + l), the orbital with lower value of n will have the lower energy.')

The text states: 'The filling of electrons into the orbitals of different atoms takes place according to the aufbau principle which is based on the Pauli’s exclusion principle, the Hund’s rule of maximum multiplicity and the relative energies of the orbitals.' Heisenberg's Uncertainty Principle is not listed as a governing rule for electron filling. (Reference: 'The filling of electrons into the orbitals of different atoms takes place according to the aufbau principle which is based on the Pauli’s exclusion principle, the Hund’s rule of maximum multiplicity and the relative energies of the orbitals.')

The text explains two ways of representing electronic configurations: 'sa pbdc ...... notation' and 'Orbital diagram'. It then states: 'The advantage of second notation over the first is that it represents all the four quantum numbers.' The orbital diagram represents spin using arrows (↑ for positive spin, ↓ for negative spin), along with n, l, and $m_l$ implicitly by the box's position. (Reference: 'The advantage of second notation over the first is that it represents all the four quantum numbers.')