Question

(i) Write the electronic configurations of the following ions: (a) H– (b) Na+ (c) O2– (d) F–
(ii) What are the atomic numbers of elements whose outermost electrons are represented by (a) 3s1 (b) 2p3 and (c) 3p5?
(iii) Which atoms are indicated by the following configurations? (a) [He] 2s1 (b) [Ne] 3s2 3p3 (c) [Ar] 4s2 3d1.

Answer 1

(i) (a) H - ion The electronic configuration of H atom is 1s 1 .A negative charge on the species indicates the gain of an electron by it.
∴ Electronic configuration of H - = 1s2
(b) Na + ion The electronic configuration of Na atom is 1s2 2s2 2p6 3s1 . A positive charge on the species indicates the loss of an electron by it.
∴ Electronic configuration of Na+ = 1s2 2s2 2p6 3s0 or 1s2 2s2 2p6
(c) O2- ion The electronic configuration of 0 atom is 1s2 2s2 2p4 . A negative charge on the species indicates that two electrons are gained by it.
∴ Electronic configuration of O2- ion = 1s22s2 p6
(d) F- ion The electronic configuration of the F atom is 1s22s22p5 . A negative charge on the species indicates the gain of an electron by it.
∴ Electron configuration of F- ion = 1s22s22p6
(ii) (a) 3s1 Completing the electron configuration of the element as 1s22s22p63s1.
∴ Number of electrons present in the atom of the element = 2 + 2 + 6 + 1 = 11
∴ The atomic number of the element = 11
(b) 2p3 Completing the electron configuration of the element as 1s22s22p3.
∴ Number of electrons present in the atom of the element = 2 + 2 + 3 = 7
∴ The atomic number of the element = 7
(c) 3p5 Completing the electron configuration of the element as 1s22s22p5.
∴ Number of electrons present in the atom of the element = 2 + 2 + 5 = 9
∴ The atomic number of the element = 9
(iii) (a) [He] 2s1 The electronic configuration of the element is [He] 2s1 = 1s22s1.
∴ The atomic number of the element = 3 Hence, the element with the electronic configuration [He] 2s1 is lithium (Li).
(b) [Ne] 3s23p3 The electronic configuration of the element is [Ne] 3s23p3= 1s 2 2s22p6 3s2 3p3 .
∴ The atomic number of the element = 15 Hence, the element with the electronic configuration [Ne] 3s23p3 is phosphorus (P).
(c) [Ar] 4s23d1 The electronic configuration of the element is [Ar] 4s2 3d1= 1s2 2s22p63s23p6 4s23d1.
∴ The atomic number of the element = 21 Hence, the element with the electronic configuration [Ar] 4s23d1 is scandium (Sc).