1. THE ATOM!

2. Atomic Number How are atoms of one element different from another?
Elements contain different number of protons!
# of protons = # of electrons
ATOMIC NUMBER (Z) is the number of protons in the nucleus.

3. Determine the number of Protons
Element Protons Atomic # Z
Carbon
Phosphorus
Gold 6 15 79

4. Mass Number – The number of protons and neutrons in the nucleus of an isotope. Mass # = p + n
Nuclide p n e mass #
Oxygen
-31 15

5. COMPLETE SYMBOL

6. Protons Neutrons Electrons Atomic # Mass #

7. Isotopes Dalton was wrong!! All elements are not identical.
Atoms of the same element can have different numbers of neutrons, so different mass #. Call them ISOTOPES!
1912 – Frederick Soddy proposed the idea. Won the nobel prize in 1921 for his work.

8. Naming Isotopes
We can put the mass number after the name of the element:
Carbon-12
Carbon-14
Uranium-235
p e n H
Protium H
Deuterium H
tritium

9. Average Atomic Mass
Elements occur in nature as mixtures of isotopes. The number on the bottom of the box of each element.
This is abundance of each isotope in nature.
Use Atomic Mass Unit (amu) – 1/12 of a C-12 atom. Has isotopic purity.

10. Average Atomic Mass
Multiply the atomic mass of each isotope by its abundance and add the results.
C % =
C % =
C-14 <0.01 =
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