Atomic number(Z):The number of electrons or protons present in an atom is called atomic number
Mass number or Atomic mass(A):The sum of protons and neutrons give us mass number

Atomic Mass

Atomic mass refers to the mass of an atom of a specific chemical element. It is commonly expressed in unified atomic mass units (u), also known as daltons (Da). The atomic mass represents the average mass of all the naturally occurring isotopes of an element, taking into account their relative abundance.

Isotopes and their Contribution

Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei. These isotopes have the same atomic number, which defines the element, but their atomic masses differ. Since different isotopes have different masses, their contribution to the atomic mass is taken into consideration when calculating the average atomic mass of an element.

Atomic Mass Calculation

The atomic mass of an element can be calculated by multiplying the mass of each isotope by its relative abundance and then summing up the results. The relative abundance is usually expressed as a percentage or a decimal. For example, if an element has two isotopes with masses of 10 u and 12 u, and their relative abundances are 20% and 80% respectively, the atomic mass would be calculated as follows:

(10 u * 0.20) + (12 u * 0.80) = 2 u + 9.6 u = 11.6 u

Therefore, the atomic mass of this element would be 11.6 u.

Atomic Number

Atomic number refers to the number of protons in the nucleus of an atom. It is a fundamental property of an element and is represented by the symbol "Z." The atomic number determines the identity of the element since each element has a unique number of protons. For example, all hydrogen atoms have an atomic number of 1, while all carbon atoms have an atomic number of 6.

Key Points:
- Atomic mass is the mass of an atom of a specific element, expressed in unified atomic mass units (u).
- Isotopes are atoms of the same element with different numbers of neutrons.
- The atomic mass considers the average mass of all naturally occurring isotopes, taking into account their relative abundance.
- Atomic mass calculation involves multiplying the mass of each isotope by its relative abundance and summing up the results.
- Atomic number is the number of protons in the nucleus of an atom, determining the element's identity.
- Each element has a unique atomic number.