The number of electrons in an atom is determined by its atomic number, which corresponds to the number of protons in the atom's nucleus. In a neutral atom, the number of electrons is equal to the number of protons.
To find the number of electrons in an atom, you can look up the atomic number of the element on the periodic table. For example:
Sodium (Na) has an atomic number of 11. This means that a neutral sodium atom has 11 electrons.
Oxygen (O) has an atomic number of 8, so a neutral oxygen atom contains 8 electrons.
Gold (Au) has an atomic number of 79, so a neutral gold atom has 79 electrons.
It's important to note that the atomic number represents the number of protons and electrons only in a neutral atom. In ions, which are atoms with a charge due to the gain or loss of electrons, the number of electrons will differ from the atomic number.
Additionally, for elements beyond hydrogen and helium, the number of electrons in each shell or energy level follows a pattern. The first energy level can hold a maximum of 2 electrons, the second level can hold up to 8 electrons, the third level can hold up to 18 electrons, and so on, following the rules of electron configuration and the filling of orbitals.