Question

What is the mass of ( in gram) of $1$ atom of sodium?

Answer 1

Mass of a substance is the amount of matter present in it but weight is the force exerted by gravity on an object. Mass of the substance remains constant but weight varies from one place to another because of change in gravity. Kilogram is the unit of mass however small masses may be measured in grams.

Complete answer:
Sodium is an alkali metal, present in the ${3^{rd}}$ period of periodic table. Sodium has atomic number $11$ and we know that Mass number = Total number of protons + Total number of neutrons.
So the atomic mass of sodium $= 11 + 12 \Rightarrow 23g$
The amount of substance that contains the same number of entities like molecules, atoms, ions, etc as the number of atoms present in $12g$ of carbon- $12$ isotope.
Moreover, the mass of $6.022 \times {10^{23}}$one mole of atom for any element in grams is equal to its gram atomic mass or one gram atom.
So, according to the question:
One mole of sodium atom contains $6.022 \times {10^{23}}$ number of sodium atoms. Therefore, the mass of $6.022 \times {10^{23}}$ number of atoms of sodium will be $23$ grams.
So, mass of one atom of sodium will be equal to$\dfrac{{23}}{{6.022 \times {{10}^{23}}}} = 3.18 \times {10^{ - 23}}$ grams.
Hence, mass of one atom of sodium = $3.18 \times {10^{ - 23}}$grams.

Note:
Avogadro’s constant is a proportionality factor that relates the number of entities or constituent particles such as atoms, molecules, ions, etc of a sample with the amount of the substance in that sample. The SI unit of Avogadro’s constant is the mole inverse i.e. $mol{e^{ - 1}}$. The value of Avogadro’s constant is equal to $6.022 \times {10^{23}}$.