1. Isotopes
- isotope: atoms of the same element that have different numbers of neutrons
- Carbon, as found in nature, is a mixture of isotopes, including atoms of carbon-12, carbon-13, and small amounts of carbon-14.

2. Isotopes
atomic weight
- The atomic weight of an element is the weighted average of the mass of its atoms based on the amount of all its naturally occurring isotopes.

3. Isotopes Isotope Symbols
mass number
atomic number
-The top number (superscript) is the mass number
-The bottom number (subscript) is the atomic number

4. Isotopes -We can also write isotopes as such:
uranium-235 or uranium-238
-The ending number is the mass of the isotope

5. Complete the following chart:
Isotope Practice
Here are three isotopes of an element:
The element is ___________.
The number 6 refers to the _____________.
The numbers 12, 13, and 14 refer to the____________.
How many protons and neutrons are in the first isotope?
How many protons and neutrons are in the second isotope?
How many protons and neutrons are in the third isotope?
Complete the following chart:
Isotope name
atomic #
mass #
# of
protons
neutrons
electrons
uranium-235
uranium-238
boron-10
boron-11