Question

Which listed element has six valence electrons?
(A) Oxygen
(B) Lithium
(C) Bromine
(D) Argon
(E) Arsenic

Answer 1

Hint: The number of atoms present in the outermost shell of an electron is known as valence electrons. These numbers determine the valency of the electrons. Valency of electrons explains the combining capacity of the electrons.

Complete step by step solution:
We have studied the Bohr’s atomic model that says that the electrons of an atom revolve around their nucleus in their specific orbitals.
His theory explained how the electrons revolve around the dense nucleus in their fixed orbitals and also explained that the electrons around the innermost shell, (that is nearest to the nucleus) have less energy and the electrons that are far away in the orbitals away from the nucleus have more energy.
Now, if we talk about valency, the first orbital, that is closest to the nucleus, namely, the K subshell has 2 electrons revolving around it. This means that the K subshell can hold up to a maximum of only two electrons.
The second orbital, namely the L subshell (n=1) can hold a maximum up to $8$ electrons.
In the third orbital, namely the M subshell (n=2) a maximum number of electrons that it can hold is $18$ electrons.
The fourth orbital, namely N subshell (n=3) can hold a maximum up to $32$ electrons.
Subsequently, 8 electrons are added with each increasing orbital.
The distribution of electrons in each subshell can be calculated by the formula ${2{{n}^{2}}}$.
Therefore, number of electrons in K subshell = ${2\times 1}$ $=2$ electrons
Number of electrons in L subshell = ${2\times 2}$ $=4$ electrons
Number of electrons in M subshell = ${2\times 3}$ $=6$ electrons

Atomic Number	Element	Electronic configuration	Valence electrons
$8$	Oxygen	$2,6$	$6$
$3$	Lithium	$2,1$	$1$
$35$	Bromine	$2,8,18,7$	$7$
$18$	Argon	$2,8,8$	$8$
$33$	Arsenic	$2,8,18,5$	$5$

Therefore, the answer is (A).

Note: The valence electrons are calculated from the atomic number and not the atomic mass of electrons. Atomic mass is the mass of the atom present in 1 atomic mass unit.