1. 101 A short lecture on Isotopes by Mr. C

2. Isotopes and the Periodic Table An element is identified by the number of its protons An atom’s mass is determined by the number of protons + neutrons Therefore, two atoms of the same element can have different masses (ISOTOPES) HOW?

3. Isotopes: Once again: An element is identified by the number of its protons And atom’s mass is determined by the number of protons + neutrons Therefore, two atoms of the same element can have different masses (ISOTOPES) if they have the same number of but different numbers of PROTONS NEUTRONS

4. Isotopes: So: 2 atoms of the same element can have different masses (ISOTOPES) if they have the same number of protons but different numbers of neutrons. Example - HYDROGEN Hydrogen-1 and Hydrogen-3 p+ p+ n n Hydrogen-1 is the most common hydrogen isotope; Hydrogen-3 (also known as tritium) is part of “heavy water” waste from nuclear power plants

5. Example - CARBON C-12 occurs most often in nature, C-13 occurs in about 5 % of all carbon, C-14 is used in carbon dating. Carbon-12 (6 p+ 6 n) Carbon-13 (6 p+ 7n) Carbon-14 (6 p+ 8n) p+p+p+p+p+p+ n n n n n n n n n nn n n n

6. ISOTOPES – so what? Because of the existence of 3 isotopes of hydrogen its atomic mass is 1.0079 amu and not exactly 1 amu. This is why in the periodic table most elements’ atomic masses are not whole numbers (they have 2 or more isotopes).