1. Atomic Structure –
cont…

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

3. Isotopes - hydrogen

4. Isotopes - chlorine
Chlorine Protons Electrons Neutrons
n

5. Isotopes - chlorine
Chlorine Protons Electrons Neutrons
n
17 17
17 17

6. Isotopes - chlorine
Chlorine Protons Electrons Neutrons
n
17 17 35-17=18
17 17 37-17 = 20

7. Isotopes
Practice Problems…..

8. Relative Atomic Mass
(Ar)
oHow we compare the
mass of atoms
oBased on Carbon
atom
oAtomic mass units
(amu)
Element Ar
H 1
C 12
O 16
Mg 24
Cl 35.5

9. Relative Atomic Mass
(Ar)
Calculate the relative atomic mass (Ar) or Chlorine.
25 % 75 %
(75x35) + (25x37)= 35.5 amu
100

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

12. Arrangement of Electrons in
Atoms
Bohr-Rutherford Diagrams