The first ionization energy of the first six elements in the periodic table is given below. H 1312.0 kJ/mol He 2372.3 Li 520.2 Be 899.4 B 800.6 C 1086.4 Why is the first ionization energy of B smaller than Be?
(a) Because the first IE tends to decreases as we go across a row of the periodic table from left to right.
(b) Because the nucleus of a B atom contains fewer protons than the nucleus of a Be atom.
(c) Because the outermost electron on B is in a 2p orbital, while in Be it is in a 2s orbital.
(d) Because the atomic number of B is odd, whereas the atomic number of Be is even.
(e) Because B has orbitals containing paired electrons while Be does not.
Answer: (c) Because the outermost electron on B is in a 2p orbital, while in Be it is in a 2s orbital.