1. ATOMIC STRUCTURE THE NUCLEUS: 1) THE PROTON:
A) WEIGH 1 AMU ( 1/12 THE MASS OF COLD CARBON, 12C ).
B) CONTRIBUTES MASS TO THE ATOM.
C) THE NUMBER OF PROTONS IS INDICATED BY THE ATOMIC NUMBER
a) THE PROTON HAS A POSITIVE CHARGE
b) INDICATES NUCLEAR CHARGE.
c) INDICATES NUMBER OF ELECTRONS IN A NEUTRAL ATOM.
d) INDICATES WHAT ELEMENT THE PARTICLE IS.
e) SPECIFIC ELEMENTS HAVE SPECIFIC ATOMIC NUMBERS( EX CARBON HAS AN ATOMIC NUMBER OF 6, 6 PROTONS, ONY CARBON HAS SIX PROTONS).
2) THE NEUTRON:
A) WEIGH 1 AMU.
B) CONTRIBUTES THE BALANCE OF MASS TO THE ATOM (THE REST IS PROTONS).
C) REDUCES PROTON REPULSION.
D) HAS NO CHARGE.
E) THE NUMBER OF NEUTRONS CAN CHANGE BETWEEN ATOMS.
F) IF TWO PARTICLES DIFFER IN THE NUMBER OF NEUTRONS RTHEY ARE CALLED ISOTOPES.

3. Calculate the average atomic weight for:
1) magnesium
mass number exact weight percent abundance

4. This is the solution for carbon:
Problem #1: Carbon
To calculate the average atomic
mass number
exact weight
percent abundance 12
98.90 13
1.10
To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures.
This is the solution for carbon:
( ) (0.9890) + ( ) (0.0110) = amu
ANOTHER EXAMPLE

5. 100 100 = 85.556 Average Atomic Mass Worksheet.
1) Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of
85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average
atomic mass of rubidium?
85.56 amu
85 X X = weighted mass = amu
85 X X = weighted mass =

6. Uranium has three common isotopes. If the abundance of 234U is 0.01%,
the abundance of 235U is 0.71%, and the abundance of 238U is 99.28%,
what is the average atomic mass of uranium?
237.98
234 X X X = mass average =
234 X .01% X 0.71% =

7. Magnesium consists of three naturally occurring isotopes
Magnesium consists of three naturally occurring isotopes. The percent abundance of these isotopes is as follows: 24Mg (78.70%), 25Mg (10.13%), and 26Mg (11.7%). The average
atomic mass of the three isotopes is amu. If the atomic mass of 25Mg is amu, and 26Mg is amu, calculate the actual atomic mass of 24Mg.