# Question #aa3b6

Aug 20, 2016

As the name suggests sub atomic particles are constituent particles of an atom, viz, Protons, Neutrons and Electrons.

We know that for any atom
Number of protons$=$ Atomic number
Number of Neutrons$=$ Mass number $-$Atomic number
Number of Electrons$=$Number of protons$=$ Atomic number

Armed with this knowledge let us find out number of sub atomic particles in a molecule of ${\text{NH}}_{3}$
One molecule of ${\text{NH}}_{3}$ has one atom of $\text{N}$ and three atoms of $\text{H}$
One atom of $\text{N}$ has
Number of protons$=$ Atomic number of $\text{N} = 7$
Number of Neutrons$=$ Mass number $-$Atomic number$= 14 - 7 = 7$
Number of Electrons$=$Number of protons$=$ Atomic number$= 7$
Number of sub atomic particles is an atom of $\text{N} = 7 + 7 + 7 = 21$

One atom of $\text{H}$ has
Number of protons$=$ Atomic number of $\text{N} = 1$
Number of Neutrons$=$ Mass number $-$Atomic number$= 1 - 1 = 0$
Number of Electrons$=$Number of protons$=$ Atomic number$= 1$
Number of sub atomic particles is an atom of $\text{N} = 1 + 0 + 1 = 2$
$\therefore$ Three atoms of $\text{H}$ have number of sub atomic particles$= 3 \times 2 = 6$

One molecule of ${\text{NH}}_{3}$ has number of sub atomic particles$= 21 + 6 = 27.$