Question

What makes up an atomic number?

Answer 1

Hint: We know that in order to answer this question, try to proceed by defining an atom. Then, describe the subatomic particles of which an atom is made. And, then you will get an idea about the atomic number and mass number of an atom. Try to remember what is the formula used to calculate the atomic number and mass number and you will get your answer.

Complete answer:
An atom is the smallest unit of matter which is composed of three subatomic particles- the proton, the neutron, and the electron. Protons are referred to as the positively charged particles present in the nucleus while electrons are the negatively charged particles that are present in the nucleus and neutrons are the neutrally charged particles present in the nucleus along with the protons.
In the periodic table the elements are arranged in an increasing order of their atomic number. From left to right in the periodic table the atomic number of an element increases. Atomic numbers always tend to be whole numbers. The number of subatomic particles corresponds to the total number of atomic mass and atomic number present. Number of protons in a neutral atom is equal to the electron present in the shell.
Protons and neutrons are responsible for the formation of atomic numbers. In the nucleus of an atom the number of protons present gives us the atomic number. Atoms of the same element exhibit the same atomic number. Atoms of different elements exhibit different atomic numbers. The atomic number is denoted by the letter $Z$.except hydrogen all other atoms consist of protons, electrons and neutrons.
The atomic number gives us the count of protons present in an atom, which helps us in arranging them in their energy level. $_{Z}^{A}X$ Here the letter $Z$ represents the atomic number whereas the letter $A$ represents atomic mass. Atomic mass is the addition of protons and neutrons in an atom.

Note:
Remember that atoms having the same number of electrons are referred to as isoelectronic atoms. Atoms of the same element having different numbers of neutrons are referred to as isotopes whereas atoms of different chemical elements have the same number of nucleons (i.e. same number of protons and neutrons).