As the atomic number of the elements in the periodic table increases, the number of electrons in the corresponding atom increases.
An atom is composed of a nucleus, containing protons and neutrons, and the electrons orbiting the nucleus. The protons are positively charged particles. A proton and an electron have electric charge that is equal in magnitude; however, the charge of an electron is negative while the charge of a proton is positive. The neutrons do not have electric charge.
Atomic number of an element is the number of protons inside the nucleus. Since the whole atom must be electrically neutral, the number of electrons orbiting the nucleus (that is, total negative charge of inside the atom) must equal the total positive charge inside the atom, which is determined by the number of protons, or atomic number. Since the magnitude of the electric charge of each proton and electron is the same, the number of electrons inside the atom always equals the number of protons. This means that when atomic number increases, the number of electrons also increases.