The atomic number represents the number of protons present in the nucleus of an atom. The atomic number of an element is located on the upper-left corner of that element in the periodic table.
Krypton's atomic number is 36, which means that there are 36 protons in the nucleus of one atom of krypton. Krypton also has 36 electrons.
Protons are positively charged, whereas electrons are negatively charged. In this way, an element cancels out the positive and negative charges to remain in an electrically neutral form. Unlike the quantity of protons in an element, the number of electrons can change. When an atom gains or loses an electron it becomes an ion, or an electrically charged atom.
If one atom of krypton were to lose one electron, it would have a positive charge of +1, because the number of protons is now exactly one greater than the revised number of electrons. An atom of an element can also have a different number of neutrons, though neutrons carry no electrical charge.
Krypton has a mass number of 84. The mass number is the sum of the number of protons and neutrons present in the nucleus of an atom. By subtracting 36 protons from the mass number of 84, it is determined that krypton has 48 neutrons. Atoms may gain or lose neutrons, and these different forms of the element are known as isotopes.