Question

1 a.m.u is equal to:
A. \[~1.66\times {{10}^{-24}}g\]
B. \[~1.66\times {{10}^{-27}}g\]
C. \[~1.66\times {{10}^{24}}g\]
D. \[~1.66\times {{10}^{24}}kg\]

Answer 1

Hint: Atomic mass unit is an international standard to weigh an element. An atom is the smallest constituent of an element which shows its entire properties. All materials are made up of atoms. The Atomic mass unit is the way to express the mass of an atom.

Formula used:
\[1\text{ a}\text{.m}\text{.u =}\dfrac{\text{Mass of }{{\text{a}}^{\text{12}}}\text{C atom}}{\text{12}}\]

Complete step by step answer:
The atom is having a size million times smaller than the thickest human hair. It has a diameter of \[{{10}^{-10}}m\]. It can’t be weighed directly. Thus, for practical purposes, the relative mass of atoms is used instead of their actual masses. The Atomic Mass Unit is the method by which the relative masses are expressed relative to that of a standard reference atom. The IUPAC accepted C-12 isotope as the standard. The mass equal to $\dfrac{1}{12}th$ of the mass of a \[^{12}C\] atom is called one atomic mass unit. ‘a.m.u’ is the abbreviation of the atomic mass unit and denoted by the symbol u.

\[1\text{ a}\text{.m}\text{.u =}\dfrac{\text{Mass of }{{\text{a}}^{\text{12}}}\text{C atom}}{\text{12}}=\dfrac{1.9924\text{ }x\text{ }{{10}^{-23}}}{12}g=1.66\times {{10}^{-24}}g\]

\[1\text{ a}\text{.m}\text{.u =}1.66\times {{10}^{-24}}g\]
Therefore, option A is the correct answer.

Additional information:
The atomic mass of elements is expressed on a relative scale based on the mass of a \[^{12}C\] atom. The relative atomic mass is a number which measures how much it is heavier than $\dfrac{1}{12}th$ the mass of a C-12 atom (or 1 a.m.u)
$\text{atomic mass =}\dfrac{\text{mass of an atom}}{\dfrac{\text{1}}{\text{12}}\text{th }\!\!~\!\!\text{ mass of C-12 atom}}$

Note: The Carbon-12 has a mass of 12 a.m.u. Carbon-12 is the most abundant isotope of carbon. Mostly the carbon will have the same number of protons and neutrons. So, we can easily find the average mass of the particle. If we are considering hydrogen instead of carbon because the atomic mass number 1. But the hydrogen isotopes are abundant in earth and won't give the perfect average mass of a particle.