Warm Up
10-1-15
Decreasing
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
Homework
-Turn in WS quiz review
-Quiz Unit 3
-Notes unit 3-4
-WS Nuclear Decay
Oct 9 - Test Unit 3
Oct 9 - Midterm Exam (45 Qs)
Oct 9 - Online HW Unit 3
Quiz Unit 3
• You may write on the quiz
• Unit 3-1 through 3-3
• 6 free response questions
Unit 3-4
Nuclear Chemistry
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)
Nuclear Force
• The nucleus is held together by residual strong
force
quarks & gluons
transfer in the nucleus
• Much stronger than the electrical repulsion
between the protons
• Stable nucleus have a ratio of 1 to 1.5 for
neutrons to protons
Radioisotopes
• Radioisotopes- unstable isotopes that gain
stability by releasing radioactive particles.
α (alpha), β (beta), and γ (gamma)
alpha
Unstable
isotope
stable
gamma
beta
Half-Life
• Half-life is the time required for half of a
radioactive substance to decay (to be stable).
-20 g sample has a halflife of 5 years. How much
is left after 10 years?
5g
-How much is left after 3
half-lives?
2.5 g
-After 4 half-lives how
many percent is still
radioactive?
6.25%
• N-13 emits beta radiation with a halflife 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
Assignments
• Summary
• Question #16 ONLY on the worksheet today
• Current event news article