Question

Electronic configuration of calcium is?
(a) $(Ar)4{{s}^ {3}} $
(b) $(Ne)3{{s}^ {2}} $
(c) $(Ar)4{{s}^ {2}} $
(d) $(Kr)4{{s}^ {2}} $

Answer 1

Hint: Here, the word electronic configuration tells us about the arrangement of electrons in the sub-shells. (it is just like the address of our house)

Complete step by step answer:
Electronic configuration is the distribution of electrons into orbitals of an atom.
• It can be represented in two ways-
I. ${{s}^{a}} {{p}^{b}} {{d}^{c}}$ .... notation
II. orbital diagram
In the first representation, the sub-shell is represented by the respective letter symbol and the number of electrons present in the subshell is depicted in the superscript, i.e., for example
$1{{s}^ {2}} $.

In orbital representation, each orbital of the sub-shell is represented by a square and the electron is represented by an upward arrow $(\uparrow) $for positive spin and by a downward arrow $(\downarrow) $a negative spin.

• For writing configuration, we should know the principal quantum numbers i.e. principle quantum number (n), azimuthal quantum number (l), magnetic quantum number (ml), spin quantum number (ms).

• Also, we have to keep some rules in our mind before writing electronic configuration. These rules are as follows-
4) AUFBAU PRINCIPLE – this rule states that ‘the orbitals are filled in order of their increasing energies’
5) PAULI EXCLUSION PRINCIPLE – it states that ‘No two electrons in an atom can have the same set of four quantum numbers’
6) HUND’S RULE – it states that in filling a particular subshell electron are first singly filled before doubly filled.
• Now, using above rules we will write electronic configuration of calcium (atomic no. is twenty)
      Ca = $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^ {2}} $
 Since we know that Argon has configuration as $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}$ , so by replacing it in calcium’s configuration. We get,
      Ca = $(Ar)4{{s}^ {2}} $


Therefore, option (c) is correct.

Note: Without knowledge of quantum numbers and some rules you will not be able to write electronic configuration, so it must be advisable that we have to ponder these rules.