+ve charged nucleus containing most of mass,
surrounded by atomic shells with orbiting
electrons containing negligible mass
Atomic/proton number gives no. of
protons in nucleus; also defines the
element and gives no. of electrons in
an ATOM
No. of electrons is same as no. of protons in an
ATOM, so atoms are electrically neutral
No. of electrons is different to no. of
protons in an ION so charged: +ve = lost
electrons, -ve = gained electrons; find
original no. of electrons in atom (atomic
no.) then add/subtract
ISOTOPES - ATOMS OF AN ELEMENT
WITH DIFFERENT NUMBERS OF
NEUTRONS AND DIFFERENT MASSES
Mass/nucleon number is no. of protons
plus no. of neutrons. Find no. of
neutrons by subtracting proton no. from
mass no.
Different isotopes of same element react in
same way - electrons involved in chemical
reactions, not neutrons