1. How Atoms Differ

2. Properties of Subatomic Particles
Symbol
Location
Relative
Charge
Relative mass
Actual mass (g)
Electron
e- or
In the space surrounding the nucleus 1- 1
1840
9.11
x 10-28
Proton
p+ or
In the nucleus 1+
1.673
x 10-24
Neutron
n0 or
1.675

3. II. Atomic Number the number of protons in an atom Identifies element
each atom has unique #
# never changes

4. III. Mass Number
represents the total number of protons and neutrons in the nucleus
# of neutrons = mass number – atomic number

5. IV. Isotopes
Atoms of the same element but have a different # of neutrons
Ex: 3 isotopes of carbon:

6. All elements have isotopes (some 2, some 3, etc.)
Some isotopes are naturally radioactive.
Ex: Plutonium

7. V. Representing Isotopes
In Ag-107, the 107 represents the mass number (neutrons + protons)
the 47 represents the number of protons

8. Practice:
1. What is the mass number for Co-59? 2. What is the mass number for 59 7

9. VI. Atomic Mass
The standard is the atomic mass unit (amu): defined as 1/12 of the mass of a carbon-12 atom
the weighted average of the isotopes of that element.
Formula:
Atomic mass of
an element = (
% abundance of
Isotope #1 x
mass
Isotope #1 ) +
Isotope #2 …

10. Practice 3 Silver has two naturally occurring isotopes.
Ag-107 has an abundance of 51.82% and mass of amu.
Ag-109 has a relative abundance of 48.18% and a mass of amu.
Calculate the atomic mass of silver.

11. Practice 4
Rubidium is a soft, silvery-white metal that has two common isotopes, Rb and Rb.
If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium? 85 37 87 37

12. Vocabulary to Know Atomic #- same # of protons & electrons
Mass #-protons + neutrons
written 2 ways: Carbon-14 or C
Isotopes-same # of protons, different # of neutrons
Atomic mass-weighted average mass 14 6