Atomic Mass

Atomic mass is the mass of an atom of an element, expressed in atomic mass units (amu). The atomic mass is determined by adding up the masses of the protons and neutrons in the nucleus of an atom.

The mass of a proton is approximately 1 amu, while the mass of a neutron is also approximately 1 amu. The mass of an electron is negligible compared to that of a proton or neutron and is not included in the calculation of atomic mass.

To calculate the atomic mass of an element, we first need to determine the number of protons and neutrons in the nucleus of its atoms. This number is also called the mass number, and it is denoted by the symbol "A". The number of protons in the nucleus, also known as the atomic number and denoted by the symbol "Z", determines the element's identity.

The atomic mass of an element is then calculated by multiplying the mass of a proton by the number of protons in the nucleus and adding the mass of a neutron by the number of neutrons in the nucleus. Mathematically, we can represent atomic mass as follows:

Atomic mass (amu) = (number of protons x mass of a proton) + (number of neutrons x mass of a neutron)

For example, the atomic mass of carbon, which has 6 protons and 6 neutrons in its nucleus, is:

Atomic mass of carbon = (6 x 1.007276 u) + (6 x 1.008665 u) = 12.0107 u

Therefore, the atomic mass of carbon is approximately 12 amu. The atomic mass of an element can vary slightly due to the presence of isotopes, which are atoms of the same element with different numbers of neutrons in their nuclei.