Question

How do you find the atomic mass of calcium?

Answer 1

Hint Atomic mass is the mass of one mole atom. The atomic mass of an element is defined as the average weight of atoms of the element relative to the carbon atom, taken as exactly $12$. For example the atomic weight of an oxygen atom is $16$ and so $\text{16gm}$ is the weight of $\text{1}\,\text{mole}$ oxygen atoms. This can be represented mathematically in the following way –
\[\text{atomic}\,\text{weight =}\,\dfrac{\text{weight}\,\text{of}\,\text{atom}\,\text{in}\,\text{gram}}{\text{number}\,\text{of mole}\,\text{of}\,\text{atoms}}\,\]

Complete Step by step solution –
The atomic mass of each element is written below the box of each element symbol in the periodic table. So, the atomic mass of calcium is$\text{40}\text{.08}{\scriptstyle{}^{\text{gm}}/{}_{\text{mol}}}$ .
Atomic mass of an element can also be determined by some following method –
(i) Dulong and petit’s method – through this method if specific heat of the atom is known so we can calculate the atomic mass of the element by calculating the approx. atomic mass and valency in the following manner –
\[\begin{align}
& \text{Approx}\text{.}\,\text{atomic}\,\text{weight = }\dfrac{\text{6}\text{.4 cal}}{\text{specific}\,\text{heat}} \\
& \text{Valency }\,\text{= }\dfrac{\text{Approx}\text{.}\,\text{atomic}\,\text{weight}}{\text{Equivalent}\,\text{weight}} \\
 & \text{Exact}\,\text{atomic}\,\text{weight = Equivalent}\,\text{weight }\!\!\times\!\!\text{ }\,\text{Valency} \\
\end{align}\]
(ii) Isomorphism method – this method is applicable when the equivalent weight of an atom is known. This is calculated through the following equation –
$\text{Atomic}\,\text{mass =}\,\text{Equivalent}\,\text{mass }\!\!\times\!\!\text{ }\,\text{valency}\,\text{of}\,\text{atom}$
(iii) Vapour density method – this method is applicable for the gaseous element. If the vapour density of a gaseous element is known, so we can calculate the atomic mass of element through following equation- $\text{Molecular}\,\text{mass}\,\text{of}\,\text{gas = }\,\text{2 }\!\!\times\!\!\text{ Vapour}\,\text{density }\!\!\{\!\!\text{ at S}\text{.T}\text{.P }\!\!\}\!\!\text{ }$

Note – In the calculation of atomic weight through Dulong and petit’s method specific heat of the element must be present in calorie.
Do not get confused with atomic mass and mass number (A). Mass number is the sum of neutrons and protons or number of nucleons present in the nucleus of the atom, and mass number is always a whole number. However atomic mass the mass of one mole atoms.