Question

Of what atoms are composed? How do we differentiate them? And what are isotopes?

Answer 1

Hint: Atoms are made up of enormous particles, protons and neutrons that are assembled into nuclei, a collection of such particles and around which electrons whizz about. The electrons have opposite charge to positively charged nuclear particles, the protons. The only exchange of electrons and sharing of electrons take place between atoms.

Complete answer:
An atom is the smallest unit of the matter that forms a chemical element. Every solid, liquid, gas and plasma is made up of neutral or ionized atoms. Atoms are extremely small, typically around $100pm$ across. It is made up of three main parts which are protons, electrons and neutrons.
The positively charged particle is known as proton, the negatively charged particle is known as electrons and the neutral particle is known as neutrons. The protons and neutrons are present in the nucleus of the atom whereas electrons revolve around the nucleus. With the help of the number of protons we can tell about the atomic number whereas with the help of the sum of the neutrons and protons we can find the atomic mass of the atom.
The simplest atom is the hydrogen $^1H$ which contains only one proton and one electron in the neutral atom. The nucleus also contains neutrons, of which a given atom could contain various numbers. This explains the existence of isotopes. Thus hydrogen contains one neutron, in addition to protons, so we got the deuterium isotope, i.e. $^2H$.
To answer this question, we will take $^{12}C$ isotope. By the definition the carbon element contains six protons, i.e. the atomic number of carbon is $6$, thus it will have six neutrons in its nucleus and around the nucleus there will be six electrons which will have various energy levels.
Most of the carbon nuclei are $^{12}C$. A few contain $7$ neutrons which give the $^{13}C$ isotope and quite few contain $8$ neutrons which give the $^{14}C$ isotope.

Note:
It is important to remember that if there are $6$ positively charged protons there must be $6$ negative extra-nuclear charges in the neutral atom, i.e. electrons which are conceived to whizz about the massive nuclear core.