how many electrons are in the nucleus of an aluminum atom?
The number of protons an atom has in its nucleus is given by the atomic number. A quick looks in the periodic table will show that aluminium has an atomic number equal to #13#. This means that any atom that is an isotope of aluminium will have #13# protons in its nucleus. Since you're dealing with a neutral atom, the number of electrons that surround the nucleus must be equal to the number of protons found in the nucleus. Therefore, the aluminium-27 isotope will have #13# electrons surrounding its nucleus. Finally, use the known mass number to determine how many neutrons you have. #color(blue)(mass number = no. of protons + no. of neutrons)#. #no. of neutrons = 27 - 13 = 14#.