Lecture 8 Summary Spontaneous, exothermic Spontaneous, endothermic.
Transfer of energy by electromagnetic waves. Spontaneous emission of radiation when the nucleus of...
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Transcript of Transfer of energy by electromagnetic waves. Spontaneous emission of radiation when the nucleus of...
What is radioactivity?Spontaneous emission of radiation when
the nucleus of an atom breaks down to form a different element.
Electromagnetic radiation is classified into two types:
Non-ionizing Radiation: Transfers energy causing vibrations, electron
excitation, and heat Parts of the spectrum: radio, microwaves, infrared,
and visible Ionizing Radiation:
High energy that ejects electrons and transforms molecules into reactive unstable fragments
Parts of the spectrum: UV, X-ray, Gamma Ray
Radio WavesWhere have you encountered radio waves?
Radio waves have the longest wavelength, smallest frequency, and ___lowest___ energy.
MicrowavesWhere have you encountered microwaves?
Microwave radiation is used to cause particles in your food to vibrate. If particles are moving faster, what does that mean for their temperature? It increases!
Microwaves have long wavelengths, low frequency, and _____low_______ energy.
InfraredWhere have you encountered infrared radiation?
Some infrared radiation is given off from the ____sun_____, which feels warm on the skin.
Infrared radiation has a long-medium wavelength, medium-low frequency, and __medium-low____ energy.
Visible LightWhere have you encountered visible radiation?
This light given off by the sun is the energy provided for ___photosynthesis____.
Visible light has a medium wavelength, medium frequency, and __medium____ energy.
Ultraviolet Where have you encountered UV radiation?
UV radiation is beneficial for the body to get Vitamin D, however overexposure kills healthy cells and leads to skin cancer. The ___ozone____ layer filters this radiation from the sun.
UV radiation has medium-short wavelength, medium-high frequency, and
_____medium-high_____ energy.
X-RayWhere have you encountered X-ray radiation?
X-rays can pass through skin/muscle but are absorbed by the bone. Why should you limit the number of x-rays you get in a year?
X-rays have a short wavelength, high frequency, and __high____ energy.
Gamma Ray
Where have you encountered gamma rays?
Gamma rays can be emitted when an atomic bomb goes off. These rays are destructive to human cells and forms of them are used in cancer treatment.
Gamma rays are emitted when ______radioactive________ elements decay.
Gamma rays have the shortest wavelength, highest frequency, and the ___highest___ energy.
Circle the radiation with the highest energy in each grouping:
gamma ray microwave visible ultraviolet radio x-ray infrared ultraviolet visible blue color red color yellow color
Background RadiationThe constant level of radioactivity always
present around usCaused by:
Cosmic rays Naturally occurring uranium Radon in the air Radioactive isotopes in food and environment
What is your radiation exposure?National Average: 500 mremBackground Average: 360 mrem
How do nuclear and chemcial reactions differ?
Nuclear reactions involve the nucleus (protons and neutrons)
BUTchemical reactions involve the
transfer and sharing of electrons
Band of Stability
After element 83 (Bismuth)the elements are naturally unstable
and may emit decay particles
The bigger the atom gets and the further from a 1:1 ratio of
protons and neutrons, the less stable the
atom is
Types of Radioactive Decay
Decay Type Symbol Charge Reaction
Particle StrengthCan be
stopped by…
AlphaBeta
Gamma
Nuclear Symbols Review
• The superscript indicates the mass number and the subscript indicates the atomic number.
C12
6
XAZ
Mass Number
Atomic NumberElement Symbol
Steps to writing decay reactions:
1. Write the nuclear symbol for the element that is given.
2. Draw an arrow.3. Identify the type of particle that has decayed
and write it after the arrow.4. Balance the mass number (top) and the
atomic number (bottom). 5. Identify the new element.
Gamma Decay Loss of a gamma particle
Does it effect the outcome of the reaction?
Alpha and gamma decay of:
00γ
239Pu 94
Half-LifeTime required for half a sample to decay
The stability of the isotope is what determines the rate of decay.
Less Stable = faster decay
Half-Life After each half-life, half of
the sample decays. Start = 100%
40 blue particles are present 1 half-life = 50%
20 blue remain 2 half-lives = 25%
10 blue remain 3 half-lives = 12.5%
5 blue remain 4 half-lives = 6.25%
2.5 blue remain
Amount never becomes zero!!
Half-Life After 10 half-lives sample considered
nonradioactive because it approaches the level of background radiation.
Because the amount never reaches zero, radioactive waste disposal and storage causes problems. Would you want radioactive waste stored in your community?
How can we get rid of nuclear radioactive waste?
Half Life PracticeExample 1:
The half-life of mercury-195 is 31 hours. If you start with a sample of 5.00 g of the sample, how much of it will still be left after 93 hours?
Half Life Practice ContExample 2:
How many half lives have passed if there is only 1.875 g left of a 30 g sample?
If the half life for this sample is 1 hour, how many total hours have gone by?
Where do we use nuclear chemistry?
Sun is powered by nuclear reactionsElectricity from nuclear power plantsMedical:
x-rays, cancer treatment, radioactive tracers Industrial:
Sterilize equipment, sterilize (irradiate) food, x-rays of metal equipment (scan for cracks in airplanes)
Military
Radiation ExposureExposure to radiation can cause cell mutations
and illness.Four factors that affect exposure:
Dose (strength of radiation) Exposure time Area exposed Tissue exposed
FissionOne heavy atom breaks down into two or more
smaller atoms and produces energyThis becomes a chain reaction
(as one atom splits and hits more, and those split and hit more)
Supercritical:creates a great release of energy - atomic bomb
Will a chain reaction always occur?Particles reacting must have critical mass:
The minimum amount of mass needed for the neutron to hit and react with
No critical mass = no reaction
Fission reactions can also be controlled to contain the energy.