Topic: Nuclear Chemistry Aim: What makes a nucleus stable? What are the 4 types of nuclear decay? Do Now: What are the two subatomic particles in the nucleus? How many p, n, & e are in an atom of K-37? HW:

Nuclear Stability Remember: Unstable nuclei Subatomic particles in the nucleus protons & neutrons Unstable nuclei have too many protons Like charges repel Bigger atomic #, more repulsion, more instability

Neutron: Proton Ratio Neutrons help stabilize the nucleus More p+ (higher atomic #) means more n are needed to stabilize the nucleus n : p ratio close to 1:1 is MOST STABLE

Neutron : Proton Ratio Larger elements tend to have larger n : p ratio (closer to 2:1)

Examples Determine n : p ratio of C 12 is mass # (p + n) 6 is atomic # (# of p) Therefore, 12 – 6 = 6 neutrons n : p ratio is 6 : 6 (or 6/6) which is 1 : 1 This isotope of carbon is stable. 12 6

Examples Determine the n : p ratio of Fe Is this nucleus stable? n : p ratio is 30 : 26 (30/26) = 1.2 : 1 This nucleus is stable 56 26

Radioactivity & Spontaneous Nuclear Decay Reference Tables N, O Radioisotope – any unstable isotope that is prone to decay (radioactive) Radioactivity - nucleus of an unstable isotope or element decays and gives off rays & particles Transmutation - nucleus of an atom decays and ONE ELEMENT CHANGES INTO ANOTHER ELEMENT!

Transmutations Natural: nucleus spontaneously decays to form a new element Nothing needs to bombard the nucleus to change it Table N radioisotopes all decay naturally (spontaneously) Artificial: transforming 1 element into another by bombarding the nucleus with high-energy particles Particle accelerators speed up the particles enough to cause an artificial transmutation How man-made elements are produced

Decay Modes Each radioactive isotope has a specific decay mode. alpha, beta, positron (all particles) gamma (rays – energy) How do we know which decay mode? REFERENCE TABLE N!!!

Alpha Decay Alpha particle emitted by nucleus of decaying radioisotope This is a helium nucleus, 2 protons & 2 neutrons (4-2) Charge of +2 Symbol – Table O

Alpha Decay

Alpha Decay Example To figure out which symbol to use for the product, see which element’s atomic # matches with your calculation!

Beta Decay Loss of beta particle Has same characteristics as an electron! Formed when a nucleus emits a neutron that converts into a proton and a beta particle Symbol:

Beta Decay

Beta Decay Example Note: mass # does not change b/c e- have no mass! Write the equation for beta decay of Carbon-14

Examples

Positron Decay Loss of a positron Symbol is e+ or β+ Antimatter equivalent of an electron Same mass as electron, opposite charge Just smile and nod. Really. Symbol is e+ or β+

Positron Decay

Positron Decay Example Write equation of positron decay of Neon-19.

Gamma Rays Loss of gamma rays Have 0 charge & 0 mass. extremely high energy photons (light) Have 0 charge & 0 mass. They’re just energy! No changes in mass or charge – just energy emitted by nucleus to help stabilize it By-product of most nuclear decay

Gamma Rays

Separating α, β-, β+ Particles, γ Rays Electric or magnetic fields can separate particles Alpha particle (charge?) deflected toward ___ electrode Beta particle (charge?) deflected toward ___ electrode Gamma ray (charge?)… + β- Radioactive Source γ α —

Sample Questions

Sample Questions

Sample Questions

Aug 05