Atoms contain subatomic particles. Electrons are negatively charged particles which are found outside the nucleus of an atom. If you use your periodic table of elements, whatever the atomic number is, which represents the amount of positive charges or protons, that is also the number of electrons the atom has. Atoms are electrically neutral. For example, the atomic number of Hydrogen is 1. Therefore, it contains 1 proton and 1 electron. Atoms in the periodic table are arranged by increasing atomic number.
Electron numbers are total number of electrons.
Examples: Electron numbers of ATOMS of Hydrogen = 1, Helium = 2,
Lithium =3, Beryllium = 4, Boron = 5, Carbon = 6, Nitrogen = 7,
Oxygen = 8, Fluorine = 9, Neon = 10, etc.
Are you refering to number of electrons in a given atom?
Electrons which are the negative particles, same as the other particles protons and neutrons in a given atom can be computed based on the atomic number and atomic weight. The atomic number is the same number of proton. Thus if an atom has an atomic number of 7 just like in the case of N, it has a number of protons equal to 7. In terms of neutral atoms, the number of proton represents the number of electron. Thus in the case of N it has a number of protons equal to 7 and electrons which is also equal to 7.