Atomic Number and Atomic Mass

Introduction

The way elements differ from each other as illustrated below:
Atomic Number and Mass

Atomic Number = Number of electrons = Number of Protons
Atomic Mass = Number of Protons + Number of Neutrons

Example

Example 1: Here is an example of the atomic mass and atomic number of Oxygen (O).
Atomic Number and Mass-2

Exercise: Finding number of protons, neutrons, and electrons

Exercise-1: Number of Atoms

Check your answers here:
Solutions

Isotopes

These are atoms of a given element that differ in the number of neutrons and consequently in mass.
Example: Oxygne isotopes as shown below where each one is called a nuclide. ¹⁶O, ¹⁷O, ¹⁸O
where ¹⁸O is the most abundant (99.762% natural abundance).

Exercise: Isotopes of Magnesium

Exercise-1: Isotopes

Check your answers here:
Solutions