Question

What is the atomic number of the atom?

Answer 1

Hint: An atom consists of protons and neutrons (together known as nucleons) in nucleus and electrons revolving around the nucleus. The number of protons and electrons are equal in an atom so that net charge on the atom is zero. For every element, the number of protons and electrons are unique.

Complete answer:
An atom consists of electrons, protons and neutrons. Electrons in an atom revolve around the nucleus in stationary orbits but protons and neutrons are present in the nucleus. Number of protons and number of electrons in a particular atom is the same and is known as its atomic number.
Atomic number is a unique property of an element since an element consists of the same type of atom and every element is defined by the number of protons it has.

Additional Information:
Since the mass of an electron is negligible as compared to that of proton and neutron, mass of an atom is considered to be concentrated at its nucleus. That means, the mass of an atom relies on the number of neutrons and protons. Protons and neutrons are together named as nucleons. Thus, the mass number of an atom is the number of nucleons present in its nucleus.

Note:
Students often make mistakes while writing notations of an atom. While writing the notation of an atom of an element, its mass number is written at the top left and atomic number is written at the bottom left of the symbol of the element.
Atoms of an element can have different mass numbers and are known as isotopes of the element.