Please take out your nuclear chemistry notes/ worksheet and turn to your three homework problems. Please take out a sheet of notebook paper. Nuclear equation quiz Tomorrow! So listen good today Ch 10 Nuclear Chemistry

Nucleus of the Atom Nuclei are made up of protons and neutrons. Collectively called ‘nucleons’ In nuclear chemistry an atom is called a nuclide and referred to the number of mass number Protons and neutrons are packed very closely together and contain the mass of the atom.

Fundamental forces in the nucleus Strong nuclear: powerful force that holds protons and neutrons together Weak Force: acts over a short range- radioactive decay Electromagnetic force: attraction and repulsion of charged particles Gravity: attractive force- acts between any two masses

Mass Defect Most of the time the total number of protons, neutrons and electrons adds up to the total mass of the atom. When the actual mass is different from the expected mass this is a mass defect. This difference comes from Einsteins famous E=mc2 equation. Some difference in mass comes from a conversion of mass to energy when a nucleus is created.

Radioactivity An unstable nucleus can emit radiation charged particles energy All atoms with more than 83 protons are radioactive. Almost all elements with more than 83 protons do not exist in nature and they decay rapidly soon after they are created.

Radioactive Decay: Nuclear Stability Most stable ratio 1:1 protons: neutrons Small elements- stable Larger elements- less stable radioactive

Nuclear Radiation – charged particles and energy (radiation) Alpha Decay: + particle made of 2 protons and 2 neutrons The same as a He atom. Symbol:  Symbol :42He 4 = mass # = p + n 2 = atomic # = p Paper can block alpha particles- least penetrating Heaviest form- loses energy as it moves

Alpha Decay of Uranium Uranium 238 undergoes Alpha decay: It loses 2 protons and 4 amu (atomic mass) To become Th-234 It loses one alpha particle which has the same number of protons and mass of the He-2 atom.

Beta Particles metal can block, faster and more penetrating than alpha Negative radiation An electron emitted by an unstable nucleus. Symbol:  Symbol: 0-1 e A neutron decays into a proton & e-. e- is emitted & proton remains trapped. metal can block, faster and more penetrating than alpha

Gamma Decay Radiation with no mass & no charge. Ray of energy Symbol:  Atomic number and mass number remain the same but the nucleus loses energy. Electromagnetic waves that travel at the speed of light. Can pass through most metal, but most blocked by thick concrete

How do we measure radiation? Geiger Counter Uses a gas filled tube to measure ionization radiation If a radioactive particle penetrates the tube through which a high potential difference is applied. This discharge is registered on the counter

Half-Life The time required for half of a radioisotope sample to decay After 1 half life, half of the original sample is left and half has decayed into the daughter element After 2 half-lives, only a quarter of the original sample still exists.

Half-lives can vary from fractions of seconds to billions of years. Nuclear decay is constant and is not affected by varying conditions. We can use the 1/2 lives to determine the age of A sample

Carbon Dating- Bones Every plant and animal has Carbon in their body- you get it form the food you eat. When an organism dies the carbon-14 levels will not go up. The carbon-14 will decay into Nitrogen-14. Scienctists use the ratio of Nitrogen to Carbon to determine how much of the original sample remains. They know the half-life of Carbon-14 and can date the sample.

Quick-Lab: Modeling ½ Life p 300 Copy Purpose: Analyze data to calculate the “half-life” of a model radioactive element Copy and answer hypothesis from board. Procedure: Follow on page 300 You will get a zero if you eat anything in lab! I reuse the candy! Instead of wallpaper squares we have candy hearts Need to count out total hearts between partners- this is your starting “mass” Work in groups of two Roles: one counters & one recorder Turn-In (Stapled together) Purpose and hypothesis. One data table AND GRAPH with groups results Answers the Analyze and Conclude Q’s (Draw a chart)

Nuclear Fission Splitting of atomic nuclei into 2 smaller nuclei of approx. equal mass. U-235 undergoes fission Not much energy is produced from one atom- only when a chain reaction occurs Chain reactions are caused when the smaller parts collide into other nuclei and continue the process. Chain reactions release huge quantities of ENERGY!

Examples of Nuclear Fission Nuclear Weapons- release all energy at once

Ex: Nuclear Power Plants Plants monitor controlled fission of U-235 to generate energy. Energy heats water to make steam which turns the turbine of a generator Steam condenses to liquid water which is re- used in the reactor core

Nuclear Fusion Combining of two nuclei form a larger nucleus of larger mass A lot of energy is released . The sun is powered by fusion of Hydrogen to Helium High temps are needed for fusion (10,000,000 °C).

Video-Field Trip- Nuclear Medicine What is nuclear medicine? If radioactive substances are used today to treat certain types of cancer, how was it possible for Marie Curie and Irene Curie to develop a form of cancer by working with radioactive substances?