Atomic Number, Mass Number, Isotope

Atoms are the basic building blocks of matter. Each element on the periodic table consists of atoms.
Every atom is made up of a nucleus that contains protons and neutrons, with electrons revolving in various energy levels around the nucleus.
Atomic number: This is the number denoted with ‘Z’ that signifies the number of protons in an atom’s nucleus. It is unique to each element. For instance, the atomic number of hydrogen is 1, meaning it has 1 proton.
Mass number, depicted by ‘A’, is the total number of protons and neutrons in the nucleus of an atom. It can vary for isotopes of the same element.
An element’s identity is determined by its atomic number. Two atoms with the same number of protons belong to the same element, regardless of the number of neutrons or electrons they have.
Isotopes are two or more forms of the same element that contain the same number of protons but a different number of neutrons. Although they have different mass numbers, isotopes of an element are chemically very similar because they have the same number of electrons.
For example, Carbon-12, Carbon-13, and Carbon-14 are isotopes of carbon. They all have 6 protons but have 6, 7, and 8 neutrons respectively.
Atomic mass of an element, typically found below the symbol on the periodic table, is the weighted average mass of the isotopes of that element.
The abundance and mass number of each isotope are used to calculate this average atomic mass. This number plays a significant role in determining the properties of the element.
It’s helpful to know that the periodic table is arranged in ascending order of atomic number (“the number of protons”), not mass number or atomic weight.
Understanding these basic properties of atoms and elements – atomic number, mass number, and isotopes – is fundamental to mastering the concept of atomic structure.

Now, try to use these points to answer practise questions or experiment problems to cement your understanding. Don’t forget to check your answers after each session.