#chemistry #textbook

Pg:- 35,36

Ch:- 2

Atomic mass (also known as atomic weight) refers to the weighted average mass of an atom of an element, typically expressed in atomic mass units (amu). It is primarily calculated by considering the mass and abundance of an element's isotopes.

To measure atomic mass, you need to know an element's atomic number and mass number.

1. Identify the Isotopes and Their Abundances

Each element can have several isotopes, which are atoms with the same number of protons but a different number of neutrons. For example, carbon has two common isotopes: Carbon-12 (C-12) and Carbon-13 (C-13).

2. Multiply Each Isotope's Mass by Its Abundance

The contribution of each isotope to the atomic mass is the product of its atomic mass and its relative abundance.

3. Sum the Contributions

Once you have the contributions from all the isotopes, sum them to find the atomic mass:

• The atomic mass is often not a whole number because it reflects the weighted average of all isotopes.

• The atomic mass is crucial in chemistry and physics for calculations involving moles, stoichiometry, and reactions.