Atoms can be classified based on numbers of electrons, neutrons and protons. The combined number of protons and neutrons is also known as its mass number. The number of protons an atom possesses is also known as it atomic number, which helps identify different elements. The number of neutrons an atom possesses in its nucleus will determine which isotope it is within that element. The number of electrons an atom has within the electron cloud surrounding the nucleus determines whether the atom has a charge or not. If it does have a charge, it is no longer considered an atom but rather an ion. Ions can be positively charged which are known as cations, or negatively charged which are known as anions.
For example, the element carbon has 6 protons within its nucleus. No other element has 6 protons, and so we can identify the element carbon by its atomic number of 6. A neutrally charged carbon atom also has 6 electrons, where each positive charge in the nucleus is balanced by the negative charge of the electrons, rendering it electrically neutral. Furthermore, a carbon atom typically has 6 neutrons, giving it a mass number of 12. However, there are different isotopes with 8 neutrons present within the carbon atom. This gives it a mass number of 14. Thus, understanding the atom and the terminology associated with it is crucial to understanding molecular composition and quantum chemistry.