Question

Why is the atomic mass of the sodium atom $'23$ amu?

Answer 1

We know what gram word in gram atomic mass signifies and also check the molecularity of sodium in naturally occurring form. Think about the number of atoms used to calculate gram atomic mass.

Complete answer:
We know that sodium is metal and its molecularity is one. Sodium atoms form metallic bonds but they can be separated easily because the strength of sodium metallic bonds is very less. They have only one valence electron so the strength of the metallic bond is less. The atomic mass of sodium is $23\text{ }Amu.$ Gram atomic mass is the atomic mass in grams or mass of one mole of the substance. Given the atomic mass of sodium is $23.$ The gram atomic mass of sodium is the atomic mass in grams. So the gram atomic mass of sodium is $23g.$
Sodium is an alkali metal that comes first in the $3rd$ period of the periodic table. It is the $11th$ element, that is, its atomic number is $11.$ Mass number $=$ Total number of protons $+$ Total number of neutrons Sodium atom has $11$ protons and $12$ neutrons in its nucleus. Thus, we get the atomic mass number $11+12=23.$
The atomic mass of sodium is defined by the number of massive nuclear particles. $Na$ has the atomic mass number $23$, so its atomic mass is $23\text{ }amu.$

Note:
Remember that the molar mass and gram atomic mass of sodium are the same but in general; they depend on the chemical species. Molar mass is the mass of the Avogadro number of particles. Whereas gram atomic mass is the mass of Avogadro number of atoms. Gram molecular weight is the weight of the Avogadro number of molecules.