1. What are Isotopes
Isotopes are atoms that have a different number of neutrons, but the same number of protons and electrons.
An atom is still the same element if it has different neutrons - it’s just a different version!

2. Carbon Isotopes
For example, the element carbon has 13 different isotopes!
You are familiar with C-12 (the C stands for carbon, and the 12 is it’s atomic mass)
This isotope has 6 neutrons
C-14 (atomic mass 14) is used for carbon dating and has 8 neutrons!

3. More about Isotopes
In an isotope, the number of protons and electrons never changes- only the number of neutrons is different
This means that each isotope of a particular element has a different atomic mass than another isotope of the same element
Remember: C-12 has an atomic mass of 12 and C-14 has an atomic mass of 14!

4. Count the Number of Protons and Neutrons

5. Isotope Notation
There are several different ways to write symbols for isotopes, each of which is perfectly legitimate.
The other ways to write each of these hydrogen isotopes from top to bottom are:
Hydrogen-1 or H-1
Hydrogen-2 or H-2
Hydrogen-3 or H-3
Example
Write down the three different notations for a carbon atom with 6 protons and 6 neutrons.

6. Applications of Isotopes
Structural determination of compounds
Carbon-14 is used for dating archaeological or geological materials
Medical Uses
Isotopes are used for diagnosis in medicine, Sodium and Iodine.

7. Quick Activity
Calculate the number of neutrons there are in the following isotopes (use your periodic table to find the atomic numbers)
Carbon-14
Nitrogen-15
Sulfur-35
Calcium-45
Iodine-131

8. Calculating Atomic Mass Based on Isotopes
Most elements exist as several different isotopes. For example, chlorine has two naturally occurring isotopes:
chlorine-35
chlorine-37
75.77% of the chlorine in the world exists as chlorine-35, and 24.23% exists as chlorine-37.

9. Calculating Atomic Mass Based on Isotopes
This is why the atomic masses on the periodic table are not WHOLE numbers.
If we know how much of each isotope exists in the world, we can calculate the average atomic mass of that element (which is the number you find on the periodic table).