b) Nucleus

b) simple nuclear model of the atom; protons, neutrons, and electrons

c) relative sizes of atom and nucleus

d) proton number; nucleon number; isotope; notation AZX for the representation of nuclei

nucleus

• positively charged protons + uncharged neutrons

atom

• a nucleus + negatively charged electrons

proton charge = +e

neutron charge = 0

electron charge = -e

protom relative mass = 1

neutron relative mass = 1

electron relative mass = 1/1840

for an element

• AZX

  • A = nucleon number

  • Z = proton number

isotope = an atom with the same number of protons and different number of neutrons