1. Remember we said that the atomic mass is the average of all the isotopes of an element. But what is an isotope and how is different from another atom of the same element? Isotopes are atoms of an element. They have: 1. A different number of neutrons in the nucleus. 2. The proton number stays the same. 3. May be heavier or lighter than the average mass found on the periodic table. 4. Most of the same characteristics and properties of that element. The biggest difference is the amount of neutrons in the nucleus!

2. ISOTOPES Carbon as found on the Periodic Table of Elements Carbon-14 (an isotope of carbon) 6 electrons are outside the nucleus 6 protons in the nucleus (Blue) 6 neutrons in the nucleus (white)** **Notice there are 6 protons (atomic #) and 6 neutrons because 12 (mass #) - 6 (atomic #) = 6 neutrons. 6 electrons are outside the nucleus 6 protons in the nucleus (blue) 8 neutrons in the nucleus** **Notice there are 6 protons (atomic #) and 8 neutrons because 14 (mass #) - 6 (atomic #) = 8 neutrons.

3. Isotopes So then how do we find know if an atom is an isotope or not? An isotope will always be designated by the element’s name and the mass number. For example, the isotope of carbon with a mass of 14 would look like: Carbon-14 We use the information above along with the ATOMIC NUMBER to find out our particle numbers. Let’s fill in the chart below and then eventually create a picture of what each element’s atoms look like. Element Name Mass Number NameSymbo l Atomic Mass Mass #Atomic # # of Proton s # of Neutrons # of Electrons Carbon-14--------- -- 14

4. Nuclei Comparison (set-up) 1. Draw 3 sets of circles, in your notebook (on the next left hand side) 2. Label a set of circles A, label a set B, and label a set C, 3. Pick a marker color to represent your neutrons 4. Pick a marker color to represent your protons. 5. Write in your notebook which color is representing protons, and which color is representing neutrons.

5. Nuclei Comparison (con’t) 5. In the circles, draw the protons and neutrons in the following nuclei: Set A. Hydrogen-1 and Hydrogen-2 Set B. Beryllium-9 and Beryllium-10 Set C. Boron-10 and Boron-11 6. Answer the following questions: 1. Explain why each set of nuclei you drew are considered isotopes of each other. 2. If an isotope has a higher mass number, is it heavier or lighter than the periodic table atom? WHY? 3. Look at the each set of isotopes and their mass numbers. If you had to predict which one was the most abundant (found the most) in nature, which isotope would you predict? WHY?

6. NUCLEI Comparison (answers) Hydrogen-1 and Hydrogen-2 Beryllium-9 and Beryllium-10 Boron-10 and Boron-11 2. Hydrogen-2 is heavier than Hydrogen-1 because it has more neutrons 3. Hydrogen-1 is the most abundant because the average mass on periodic table is closer to one 2. Beryllium-10 is heavier than Beryllium-9 because it has more neutrons 3.Beryllium-9 is the most abundant because the average mass on periodic table is closer to one 2. Boron-11 is heavier than Boron-10 because it has more neutrons 3.Boron-11 is the most abundant because the average mass on periodic table is closer to one