to solve this problem all we need is a periodic table bromine has a symbol br the top number on the square is the atomic number this is the number of protons in the nucleus of that element since the question said a bromine atom we can assume that the number of protons and electrons are the same since protons have a positive charge the total number of protons must be balanced by the same number of electrons because electrons have a negative charge so the numbers of electrons is 35 finally we need to figure out the number of neutrons this is called the atomic mass to answer this homework question we're going to round this number to the nearest whole number because that will tell us the mass technically it's the mass number of the most common type of that element so for bromine it would be 80. the mass number 80 is the number of protons and neutrons added together since we already know the number of protons we can subtract that from the mass number so the number of neutrons is the mass number minus the atomic number and for bromine that comes out to 45 neutron