Question

1. Which element has the following electron configuration?

(a) [He]2s1 _____________

(b) [Ne]3s23p3_____________

(c) [Ar] 4s23d104p6 _______________

(d) [He]2s22p3 _____________

(e) [Ar]4s13d10______________

(f) [Ar]4s13d5_______________

2.Write the number of core and valence electrons in Ca and Mg.

Ca has ______ core electrons and ______ valence electrons.

Mg has _______core electron and ______ valence electrons.

3.Identify the element.
(a) The element that contains 10 core electrons and 5 valence electrons. ____

(b) Its (1+) ion contains 18 core electrons and 7 valence electrons. _____

4.Rearrange the following atoms/ions in decreasing order of radius:

(a) Cl, Mg, Ca, Ba : _________________________
(b) Al3+, Mg2+, Ca2+, F−, O2− : ________________________
(c) Pb, Sn , Si, As: _________________________

5.

(a) [Ne] (b) [Ar]

write the set of isoelectronic ions (4 each) that have the same ion configuration as the noble gas

Answer 1

Answer – 1) We are given electronic configuration and we need to find out the element

We know the total electron in the electronic configuration for neutral element is the equal to its atomic number, so the following are the elements as follow –

(a) [He]2s1 = Lithium (Li)

(b) [Ne]3s23p3 = Phosphorus (P)

(c) [Ar] 4s23d104p6 = Krypton (Kr)

(d) [He]2s22p3 = Nitrogen (N)

(e) [Ar]4s13d10 = Copper (Cu)

(f) [Ar]4s13d5 = Chromium (Cr)

2) We know the core electron are the electrons which are not involved in bonding. Valance electron are the electrons which are used in chemical bonding electron or valance electrons = group number in that element present.

Ca has 18 core electrons and 2 valence electrons.

Mg has 10 core electron and 2 valence electrons

3) Now we are given the core and valance electron and from that we need to find out the element

(a) The element that contains 10 core electrons and 5 valence electrons is Phosphorus (P)

(b) Its (1+) ion contains 18 core electrons and 7 valence electrons is Manganese (Mn)

4) We know the atomic or ion radius decrease from left to right in period and it is increase from top to bottom in the group , so the following are the atoms/ions in decreasing order of radius –

(a) Cl, Mg, Ca, Ba : Ba > Ca > Mg > Cl
(b) Al3+, Mg2+, Ca2+, F−, O2− : O^2- > F^- > Ca²⁺ > Mg²⁺ > Al³⁺
(c) Pb, Sn , Si, As: PB > Sn > As > Si

5) We know isoelectrons means the which have same electrons

a) [Ne] has 10 electron

so, O^2-, F^- , Na⁺, Mg²⁺ all has 10 electron and all these ions are isoelectronic with Ne.

a) [Ar] has 18 electron

so, S^2-, Cl^- , K⁺, Ca²⁺ all has 18 electron and all these ions are isoelectronic with Ar.