The atomic mass of a given element is the sum of the masses of its isotopes, each multiplied by its natural abundance. Isotopes are atoms of the same element with the same atomic number but different mass number. Atomic number on the other hand is the number of protons in the nucleus of an atom.
Silicon is an element in group 4 in the periodic table, it has an atomic mass of 28.08. It has an atomic number 14, which means it has 14 protons in the nucleus of its atom, and thus it has 14 electrons in the energy levels, and therefore, its electronic configuration is; 2:8:4.
