Unit 6A The Nature of AtomsUnit 6A The Nature of Atoms

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What are the 3 subatomic What are the 3 subatomic particles in an atom?particles in an atom?

electron proton neutron

What are their charges?What are their charges?electron - negativeelectron - negativeproton - positiveproton - positiveneutron - neutralneutron - neutral

Where are each located?Where are each located?

electron - orbitingelectron - orbitingproton - nucleusproton - nucleusneutron - nucleusneutron - nucleus

What’s the purpose of each.What’s the purpose of each.

electron – involved in reactions with other electron – involved in reactions with other elements.elements.

proton – identifies the element.proton – identifies the element.neutron – keeps the nucleus stable.neutron – keeps the nucleus stable.

ElectromagnetismElectromagnetism

the force that deals with the force that deals with electricity and electricity and magnetism and magnetism and displays attraction or repulsion displays attraction or repulsion between charged bodiesbetween charged bodies

(fairly strong)

Strong Nuclear ForceStrong Nuclear Force

the force that holds protons the force that holds protons and neutrons in a nucleus and neutrons in a nucleus (netting)(netting)

(very strong)(very strong)

List the subatomic particles List the subatomic particles for…for…

HydrogenHydrogenHeliumHeliumLithiumLithiumCarbonCarbonGold (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???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 platesRadiation 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 RutherfordErnest 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

RutherfordRutherford’’s Gold Foil s Gold Foil ExperimentExperiment

As a result of this experiment Rutherford As a result of this experiment Rutherford proposed that atoms had a nucleus proposed that atoms had a nucleus composed of protons and neutronscomposed of protons and neutrons

Electromagnetic SpectrumElectromagnetic Spectrum

Nonionizing RadiationNonionizing Radiation

Low EnergyTransfers 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-VCan ionize atoms/molecules, making them highly

reactive, very dangerous to living cells/tissues

Nuclear RadiationNuclear Radiation

Exposure to ionizing radiation:Radioisotopes are naturalDifferent radioisotopes emit different types and

amounts of radiationEveryone receives background radiationAll life forms contain radioisotopes

(radioactive isotopes)

Three kinds of radiation emitted via Three kinds of radiation emitted via radioactive decayradioactive decay

Alpha particles stopped by paperalpha particles are helium nuclei

Beta particles stopped by aluminumbeta particles are electrons

Gamma rays stopped by leadgamma rays are high energy photonsx-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

PN

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 radiationAlpha, 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 nucleiIt 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

Mass 4amu ≈ 0 0

Charge +2 -1 0

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 is Helium nucleus electron High energy electromagnetic radiation

Comparison of Alpha, Beta, and Gamma Radiation

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 pasteurizationKills pests/microorganisms without

food degradationControls 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 dosesShort-time exposures