Question

How many valence electrons does silicon have?
(A) 28
(B) 2
(C) 14
(D) 1
(E) 4

Answer 1

Hint: Silicon belongs to group 14 in periodic table. $1s^{2}2s^{2}2p^{6}3s^{2}3p^2$is electronic configuration of silicon in ground state. Atomic number of silicon is 14. In its outermost shell, four electrons are present. It is placed below carbon in the periodic table.

Complete solution step by step:
-Atomic number of silicon is 14.
-It belongs to group 14 of periodic table. Group 14 elements are also a carbon family.
-It is placed below carbon in periodic table.
-Electronic configuration of silicon is $$1s^{2}2s^{2}2p^{6}3s^{2}3p^2$$.
-In the first shell, it has two electrons. In the second shell, it has eight electrons.
-In the outermost shell that is the third shell it has four electrons.
-Valence electrons are electrons of the outermost shell which can participate in chemical bonding.
-To complete octet, silicon forms bonds with four other atoms.
-The outermost shell electronic configuration for silicon is $3s^{2}3p^2$. Two electrons are present in 3s orbital and two electrons are present in 3p orbital.
-Valence electrons can be calculated by determined using following steps:
When atomic number of elements is known, electronic configuration should be written according to Aufbau principle, then valence electrons are the number of electrons present in the outermost shell.
-As in silicon, four electrons are present in the outermost shell, so silicon has Four valence electrons.

-Correct option is (E) 4.

Note: Atomic number of silicon is 14. So electronic configuration according to Aufbau principle is $1s^{2}2s^{2}2p^{6}3s^{2}3p^2$.Valence electrons are electrons present in outermost shell. Also, the first shell gets filled with 2 electrons, the second shell with 8 electrons so remaining four electrons are filled in the outermost third shell.