Chapter 10 Radioactivity and Nuclear reactions

Radioactivity and Nuclear reactions Chemical reactions occur by the rearrangement of electrons to make different bonds with other atoms Nuclear reactions occur by a change in an atom’s nucleus (where the protons and neutrons are stored) Radioactivity – the emission of subatomic particles or high-energy electromagnetic radiation by the nuclei of certain atoms

Isotope symbol A = Mass number, Sum of protons and neutrons in nucleus Z = Atomic number, the number of protons in the nucleus X = Chemical symbol Certain Isotopes can be refered to as nuclides 11 neutrons and 10 protons 10 neutrons and 10 protons

Subatomic particle notation Proton symbol Neutron symbol Electron symbol Positron symbol Mass number still in top left corner Number of protons still in bottom left corner

Types of radioactivity Alpha (α) decay – occurs when an unstable nucleus emits a particle consisting of two protons and two neutrons This adds up to a helium nucleus Alpha particle = Can represent process through a nuclear reaction Mass number and protons must be balanced

Alpha decay continuted Highly energetic radiation (like alpha decay) can interact and damage other molecules (like biological molecules) Alpha decay has the highest ionizing power due to its large size, but also has the lowest penetrating power because of its large size

Beta (β) decay Beta (β) decay – when an unstable nucleus emits an electron Through a neutron changing into a proton, an electron can be emitted from the nucleus Remember that all protons and neutrons must still be balanced in the equation Smaller size means less ionizing power, but better penetrating power

Gamma (γ) ray emission Gamma (γ) rays – high energy short wavelength photons Gamma ray symbol Alpha emission also occurs with gamma emission Has the lowest ionizing power, but the highest penetrating power

Positron Emission Positron – the antiparticle of an electron, same mass but with opposite charge When a proton changes into an neutron a positron is emitted Positrons have the same ionization and penetration power as beta particles

Electron capture Electron capture – when a nucleus assimilates an electron from an inner orbital of its electron cloud A proton and an electron combine to make a neutron

Practice Identify the emission types

Practice continued Fill in the empty position to balance the nuclear equation, then identify type of radiation

Practice continued Draw the equations for 238-uranium undergoing alpha decay, beta decay, positron emission, and electron capture

Half-life (t1/2) Half-life – (t1/2) the amount it takes for half of a radioactive sample to decay. Half-life is independent of size, temperature, and pressure Half-life is different for every element

Practice If you have 20g of carbon, how much will you have after one half life? How much after a total of two half-lifes? If the half life of Cobalt-60 is 5.3 years, how many years will it take a 100g sample to decay to 25g?

Nuclear Fission Nuclear fission – splitting of atoms Bombarding uranium (specifically U-235) with neutrons causes nuclear fission -- the splitting of the uranium atom Process releases a large amount of energy 3 neutrons are produced that can cause 3 more U-235 isotopes to undergo fission, this is a chain reaction

Nuclear Fusion Nuclear Fusion – combining of atoms Produces about 1000 times more energy than fission Mechanism behind the hydrogen bomb

Chapter 10 Review Radioactivity Types of radioactive decay Half-life Nuclear Fission and Fusion