1. 3.00_Chemistry of Biology Biology I (Isotopes)
Slides 70-82

2. Isotopes
All atoms of an element have the same number of protons. However, they may have different number of neutrons.
Atoms with the same number of protons and a different number of neutrons are called isotopes.
An isotope is identified by its mass number, which is the sum of the protons and neutrons in the nucleus.

3. What are Isotopes?

4. Isotopes Notation

5. Isotopes and Elements Practice Problems

6. Isotopes
All the atoms of a particular element have the same number of protons. It is the number of protons which determine the chemical properties of an atom. This is because the number of protons determines the number of electrons which orbit the nucleus. The number of neutrons however can vary.
Atoms of the same element that have the same number of protons but different number of neutrons are called isotopes of that element.
Or in other words, atoms of the same element with the same atomic number but different atomic masses are called isotopes of that element.
The Three Isotopes of Hydrogen (H)

7. Isotopes
Atoms of the same element that HAVE A DIFFERENT NUMBER OF NEUTRONS
Some isotopes are radioactive. This means that their nuclei is unstable and will break down at a CONSTANT RATE over time.
There are several practical uses for radioactive isotopes:
CARBON DATING
TRACERS
KILL BACTERIA / CANCER CELLS

8. Isotopes: Different Forms of the Same Element
In any element, the # of protons is always constant.
Unlike the number of protons, the number of electrons and neutrons can vary within an element without changing the identity of the element.
Ex. Carbon (C) ALWAYS has 6 protons, but it can have anywhere from 6-8 neutrons and 2-10 electrons

9. Isotopes
An ISOTOPE is a form of an element that has a different number of neutrons than “normal”
Carbon has three isotopes
Notice how the # of protons does NOT change!

10. Isotopes
Atoms of the same element that have the same number of protons and electrons but have a different number of neutrons

11. Isotopes

12. Other Isotopes Most atoms have naturally occurring isotopes including:
Radon
Potassium
Uranium
When an element is “radioactive” it means it has an unstable number of neutrons (an unstable ISOTOPE)

13. Radioactive Isotopes
When a nucleus breaks apart, it gives off radiation that can be detected and used for many applications.
Examples include Carbon dating and radiation therapy to treat cancer.

14. Periodic Table on the Isotopes
The elements, as they are found on the periodic table, are neutral atoms and their mass is an average of all isotopes
Remember the atomic mass is the average of ALL isotopes, but when we round it for calculating the number of neutrons, we always get the most abundant isotope.