2. Isotopes
Elements are defined by the number of protons
(atomic #, Z).
Atoms of an element with the same # of protons and
electrons, but different # of neutrons.
◦ Same atomic # (Z) but different mass # (A)
◦ Same chemical properties, however some are radioactive
10. Arrangement of Electrons in
Atoms
Electrons move very fast around the
nucleus
It is impossible to pinpoint their
location
Electrons are arranged in energy levels
and cannot be between them.
11. Arrangement of Electrons in
Atoms
1st level – 2
2nd level – 8
3rd level – 18 (when 8 are present next two
jump to level-4, then following return to
level-3)
4th level - 2