Question

What is the atomic mass of Sodium?
(a). 22 g/mol
(b). 23 g/mol
(c). 11 g/mol
(d). 20 g/mol

Answer 1

- Hint: Atomic mass of an element can be determined from knowing the atomic number of the element and the number of neutrons present. In case of sodium the atomic number is 11.
Formula used: Atomic number + Number of neutrons

Complete step by step answer:
Sodium is an alkali metal. It holds its place in the periodic table as the first element of the 3rd period. It is the eleventh element in the periodic table. Therefore,
The atomic number of Sodium = 11,
Number of neutrons in the nucleus of the Sodium ion = 12
The atomic mass of Sodium $=11+12=23$
Hence, 1 mole of Sodium weighs 23 grams.
We know,
        Since the atomic mass of Sodium is 23, we can also write it as 23 g/mol.
Therefore, we conclude that Option B is the correct answer.

Additional Information:
The atomic number of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons. Atomic number is denoted by the symbol Z.
The atomic mass is the mass of an atom. Although the SI unit of mass is the kilogram, the atomic mass is often expressed in the non SI-unit dalton, where one dalton is defined 1/12 of the mass of a single carbon-12 atom, at rest. The protons and neutrons of the nucleus account for nearly all of the total mass of atoms, with electrons and nuclear binding energy making minor contributions. Thus, the numeric value of the atomic mass when expressed in the daltons has nearly the same value as the mass number.

Note: Atomic mass is a dimensionless quantity. Since the atomic number of sodium is 11, it has got 1 electron in the valence shell. Therefore, the valency of sodium is 1. The number of protons is equal to the number of electrons in sodium. But when sodium loses one electron to attain the octet configuration, sodium becomes an ion with +1 positive charge.