Atoms and Isotopes the light bulb is a reminder 4/24/2017 Atoms and Isotopes the light bulb is a reminder you need to do something on your notes page

What are isotopes? Key Why are all these atoms still called CARBON? 4/24/2017 What are isotopes? Atoms of an element that have different masses This occurs by changing the number of neutrons in the nucleus. Key AMU = atomic mass unit Carbon-12 atomic mass = 12 AMU 6 p+ and 6 n = 12 AMU Carbon-13 atomic mass = 13 AMU 6 p+ and 7 n = 13 AMU Carbon-14 atomic mass = 14 AMU 6 p+ and 8 n = 14 AMU Why are all these atoms still called CARBON? Slide 1

What are isotopes? Key Isotopes of Hydrogen H H H Standard atomic notation Hydrogen-1 atomic mass = 1 AMU 1 p+ and 0 n = 1 AMU AMU = atomic mass unit 1 H 1 Periodic Table Notation Mass number on top Hydrogen-2 (deuterium) atomic mass = 2 AMU 1 p+ and 1 n = 2 AMU 2 H 1 Atomic number on bottom Hydrogen-3 (tritium) atomic mass = 3 AMU 1 p+ and 2 n = 3 AMU 3 H 1  Hydrogen is the only element that has different names for its isotopes Slide 2

Isotopes are written using standard atomic notation. Potassium has three isotopes, Potassium is found in nature in a certain ratio of isotopes. 93.2% is potassium-39, 1.0% is potassium-40, and 6.7% is potassium-41 Atomic mass = (0.932 x 39) + (0.001 x 40) + (0.067 x 41) = 39.1 AMU So why is the mass of K listed as 39.1 AMU? AMU = atomic mass unit Slide 3

What is Radioactivity? Elements that are RADIOACTIVE have nuclei that is UNSTABLE. Why is this nucleus unstable? Count up the number of protons and neutrons – are there more attractive or repulsive forces in this nucleus? A nucleus is unstable if it has too many particles in the nucleus. To become STABLE, they give up particles or energy and this is……. Radioactivity Slide 4

What is Radioactivity? The strong nuclear force holds the protons and neutrons together but when the repulsive force of the protons gets too large then the atom undergoes radioactive decay. Slide 5

Radioactive Decay Parent nucleus (unstable) Daughter nucleus Radioactivity released The radioactivity released can be particles or energy Slide 6

What is Radioactivity? Slide 7

Radioactivity All elements have at least one radioactive isotope. 4/24/2017 Radioactivity All elements have at least one radioactive isotope. All isotopes with atomic number greater than 83 are radioactive. Graph of Stable and Unstable isotopes Example: Uranium-238 Proton number = 92 Neutrons = 146 Slide 8

Periodic Table Slide 9

Uranium 238 decay (U-238) Unstable parent nucleus First decay product Q: Why is the mass of the daughter nucleus less than the mass of the parent nucleus? A: The daughter nucleus has LOST neutrons to become stable. Q: Why is the atomic number of the daughter nucleus less than the atomic number of the parent nucleus? A: The daughter nucleus has LOST protons to become stable and has become a different element. Stable daughter nucleus Slide 10

Uranium 238 decay The half life of U-238 is 4.5 billion years. If you start with 100 g of U-238 4.5 billion years later you have 50 g of U-238 (half of parent left) 50 g of Pb-82 (new daughter element) Slide 11