1. Atomic Structure

2. Definitions:
1. Atom – smallest particle, building block of all substances
2. Ion – element with a charge due to loss or gain of electrons
3. Isotope – element with the same number of protons but a different number of neutrons (mass number will change)
4. Atomic Number – number of protons; small, whole number on the periodic table
5. Mass Number – number of protons plus neutrons; this is the nuclear mass
6. Average Atomic Mass – weighted average of all isotopes

3. Particle
Mass
Location
Protons
1 amu
nucleus
Neutrons
Electrons
1/1840 amu
energy levels

4. Ways to write elements
I. Isotope
Carbon – (element name – mass #)
C (symbol – mass#)
Nuclear Symbol
12C (12 = mass#, 6 = atomic #) 6
31P-3 (31 = mass#, 15 = atomic #, = charge)

5. Calculating Average Atomic Mass
-since this is a weighted average, we must use percentages to calculate. All percentages of isotopes of an element must equal 100%
Steps:
Convert percentage to decimal
(divide by 100 OR move decimal 2 places to left)
Multiply decimal by mass number
Add together

6. Ex. What is the average atomic mass for an element that is 75% N-14, 20% N-15, and 5% N-16?