1. Warm Up 10-1-15 1.Where are the biggest atoms on the periodic table? 2.Arrange the following elements in increasing electronegativity: Cl, As, Sn 3.Which trend(s) describe this graph Agenda -Turn in WS quiz review -Quiz Unit 3 -Notes unit 3-4 -WS Nuclear Decay Homework Oct 9 - Test Unit 3 Oct 9 - Midterm Exam (45 Qs) Oct 9 - Online HW Unit 3 Decreasing

2. Quiz Unit 3 You may write on the quiz Unit 3-1 through 3-3 6 free response questions

3. Unit 3-4 Nuclear Chemistry

4. Nuclear Reactions  Chemical Reactions: Atoms rearrange to form new substances, but atoms’ identities do not change. (electrons change, but nucleus remains the same)  Nuclear Reactions: Chemical RxN that involves the changing of an atom’s nucleus. Large amounts of energy released compared to chemical reactions (mass defect)

5. Nuclear Force The nucleus is held together by residual strong force Much stronger than the electrical repulsion between the protons Stable nucleus have a ratio of 1 to 1.5 for neutrons to protons quarks & gluons transfer in the nucleus

6. Radioisotopes Radioisotopes- unstable isotopes that gain stability by releasing radioactive particles. α (alpha), β (beta), and γ (gamma) Unstable isotope stable alpha beta gamma

7. Half-Life Half-life is the time required for half of a radioactive substance to decay (to be stable). -20 g sample has a half- life of 5 years. How much is left after 10 years? 5 g -How much is left after 3 half-lives? 2.5 g -After 4 half-lives how many percent is still radioactive? 6.25%

8. N-13 emits beta radiation with a half- life of 10 min. How long is three half lives? – 30 min How many grams of the isotope will be left if there were 10 g of N-13? – 1.25 g

9. Assignments Summary Question #16 ONLY on the worksheet today Current event news article