1. Isotopes and Average Atomic Mass

2. Scientists have discovered that each element consists of atoms that are virtually identical. There is a notable exception, however. While the element carbon is defined as being made up of neutral atoms with 6 protons and 6 electrons, not every carbon atom has the same number of neutrons. Carbon has three naturally occurring isotopes.

3. What are Isotopes? O Atoms of the same element that have different numbers of neutrons (same # of electrons and protons), therefore, different mass numbers (atomic mass).

5. How many isotopes can an element have? O All elements have a number of isotopes. Hydrogen has the fewest number of isotopes with only three. The elements with the most isotopes are cesium and xenon with 36 known isotopes.

6. Stable and Unstable Isotopes O Some isotopes are stable and some are unstable. O When an isotope is unstable it will decay over time and eventually it will turn into another isotope or element. O Unstable isotopes are considered radioactive. Most elements that are found in nature are made up of stable isotopes. O The element with the most stable isotopes is tin which has ten different stable isotopes.

7. Writing a symbol for an Isotopes?

8. Calculating Average Atomic Mass

9. Calculating average atomic mass In order to determine the atomic weight of an element accurately, the atomic masses of the isotopes and the percentage of each isotope must be arrived at experimentally, and calculated.

10. Calculating Average Atomic Mass

11. Example # 1