Unit 6A The Nature of Atoms Copy words in RED Copy words in RED

What are the 3 subatomic particles in an atom? electron proton neutron What are their charges? electron - negative electron - negative proton - positive proton - positive neutron - neutral neutron - neutral

Where are each located? electron - orbiting electron - orbiting proton - nucleus proton - nucleus neutron - nucleus neutron - nucleus

What’s the purpose of each. electron – involved in reactions with other elements. electron – involved in reactions with other elements. proton – identifies the element. proton – identifies the element. neutron – keeps the nucleus stable. neutron – keeps the nucleus stable.

Electromagnetism the force that deals with electricity and magnetism and displays attraction or repulsion between charged bodies the force that deals with electricity and magnetism and displays attraction or repulsion between charged bodies (fairly strong)

Strong Nuclear Force the force that holds protons and neutrons in a nucleus (netting) the force that holds protons and neutrons in a nucleus (netting) (very strong)

List the subatomic particles for… Hydrogen Hydrogen Helium Helium Lithium Lithium Carbon Carbon Gold (Au) Gold (Au) Radium (Ra) Radium (Ra) Uranium (U) Uranium (U) Plutonium (Pu) Plutonium (Pu)

An unstable nucleus releases energy by emitting radiation during the process of radioactive decay. An atom with an unstable nucleus is called a radioisotope. Mass number Atomic number Ex) U-238

How do we know this??? Study of the Atom began with study of Radiation 1895 German, W K Roentgen studies Fluorescence – emission of light when struck with radiant E ( ultraviolet) Accidentally discovered mysterious source of radiation, soon called X-rays Cathode Ray Tube (CRT)

1896 French physicist Henri Becquerel discovered radiation more powerful than X-rays when U-containing mineral (Pitchblende) exposed photographic plates Radiation is stronger than X-rays Uranium Salt Photographic film Cloudy day / Dark drawer for a couple days Much, much larger effect! The uranium itself was emitting radiation!

1903 French scientist Marie Curie & husband Pierre isolated Polonium and Radium from Pitchblende ore In 1934 she died from leukemia caused by her long-term exposure to radiation.

Ernest Rutherford English physicist developed a more modern model of the atom Performed the “gold foil experiment” with Hans Geiger and Ernest Marsden Geiger counter – measures counts per minute (CPM) of ionizing radiation

Rutherford’s Gold Foil Experiment As a result of this experiment Rutherford proposed that atoms had a nucleus composed of protons and neutrons As a result of this experiment Rutherford proposed that atoms had a nucleus composed of protons and neutrons

Electromagnetic Spectrum

Nonionizing Radiation Low Energy Transfers all its E to matter, causing atoms to vibrate or move e- to higher energy levels (light) Excessive exposure can be dangerous (ex. sunburn)

Ionizing Radiation High Energy Alpha, beta, & gamma radiation, X-rays, U-V Can ionize atoms/molecules, making them highly reactive, very dangerous to living cells/tissues

Nuclear Radiation Exposure to ionizing radiation: Radioisotopes are natural Different radioisotopes emit different types and amounts of radiation Everyone receives background radiation All life forms contain radioisotopes (radioactive isotopes)

Three kinds of radiation emitted via radioactive decay Alpha particles stopped by paper alpha particles are helium nuclei Beta particles stopped by aluminum beta particles are electrons Gamma rays stopped by lead gamma rays are high energy photons x-rays similar, but lower energy than gamma

Alpha particles are the least penetrating. Gamma rays are the most penetrating. 25.1

Alpha Radiation (  ) Particle released when the nucleus kicks out 2 neutrons and 2 protons Relatively massive Relatively slow Total charge of +2 Mass number changes by 4 and atomic number changes by 2

Beta Radiation (  ) Particle released when the nucleus changes a neutron into a proton and a beta particle Relatively small mass Relatively fast moving Total charge of -1 Mass Number remains constant  P N

Gamma Radiation (  ) Pure energy. Released from the nucleus when an alpha or a beta is emitted No mass Speed of light No charge

Nuclear Radiation form of ionizing radiation that results from nuclear changes Radioactive atoms have unstable nuclei, emitting subatomic particles and E Radioactive atoms may change to other elements if atomic # changes (handout)

Alpha, beta and gamma radiation Alpha particles deflected by magnet Gamma rays unperturbed by magnet Beta particles deflected opposite alpha Alpha particles were discovered to be helium nuclei It was noticed early on that beta particles behaved exactly like cathode rays (electrons) Gamma rays were very high energy x-rays (photons)

particle Alpha  Beta  Gamma  Mass4amu≈ 00 Charge+20 Effect on nucleus loses two protons and two neutrons The ELEMENT changes converts a neutron to a proton & ejects an electron The ELEMENT changes loses energy The element does not change What it isHelium nucleuselectronHigh energy electromagnetic radiation Comparison of Alpha, Beta, and Gamma Radiation

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Most sensitive cells: Rapidly dividing cells (Small intestines, bone marrow, hair, fetus) Least sensitive cells: Slowly dividing cells (brain, nerves)

Time Distance Shielding Containment

Radon from U-rich soil/rock

Food treatment comparable to pasteurization Kills pests/microorganisms without food degradation Controls sprouting Does not make the food radioactive FDA Approved Must be labeled

Smoke Detection Equipment Self-powered Lighting in Exit Signs Lighted Aircraft Instrumentation Pharmaceutical Detection Bomb/Weapons Detection Scanning and Surveillance Equipment Theft Deterrent Systems

Eliminate dust from computer disks & audio & video tapes Sterilize baby powder, bandages, cosmetics, hair products, & contact lens solutions Control thickness of sheet products Attach a non-stick surface to pans Brighten porcelain in false teeth

Small radioactive sources have provided heat and electrical power for space probes for decades Radioactive power supplies have allowed space craft to explore the outer solar system, too far from the sun for solar panels to be effective

X-radiation Radiographs Fluoroscopy CT scan Nuclear Medicine Generally low doses Short-time exposures