Paper: CSIR-NET December 2013 · Subject: Inorganic Chemistry · Chapter: Chemical Bonding · Topic: Chemical Bonding – General · Marks: 2 · Difficulty: Easy
The energy of 2s and 2p orbitals is the same for
(a)Li
(b)$\mathrm{Li^{2+}}$
(c)$\mathrm{Be}^{2+}$
(d)$\mathrm{H}^{-}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Li²⁺ is the only one-electron species among the options, so its 2s and 2p orbitals are degenerate.
Explanation
Li²⁺ (1s¹) is a one-electron, hydrogen-like ion. With no other electron to screen the nucleus, orbital energy depends only on n, so 2s and 2p are degenerate. Li (1s²2s¹), Be²⁺ (1s²) and H⁻ (1s²) all have two or more electrons; screening and penetration then make E(2s) < E(2p). Answer: (b) Li²⁺.