One neutral atom of bromine has 35 protons, 35 electrons and 45 neutrons, according to ChemicalElements.com. Bromine has an atomic number of 35.
Because an element's atomic number corresponds to the number of protons in one atom of the element, bromine must have 35 protons. A neutral atom must have the same number of protons and electrons, so bromine also has 35 electrons.
An easy way to determine the number of neutrons in an element is to subtract the number of protons in the element from the element's mass number. The mass number is obtained by rounding the atomic weight to the nearest whole number.
Bromine's atomic weight of 79.9 rounds to 80. Subtracting 35 protons from a mass number of 80 gives a result of 45.