AP Chemistry Chapter 23 Notes. Henri Becquerel ruined some photographic plates with x-rays from a...
-
Upload
anis-spencer -
Category
Documents
-
view
216 -
download
0
Transcript of AP Chemistry Chapter 23 Notes. Henri Becquerel ruined some photographic plates with x-rays from a...
AP Chemistry
Chapter 23 Notes
Henri Becquerel ruined some photographic plates with x-rays from a uranium source and radioactive decay was discovered in 1896.
Henri Becquerel’s experiment – (1896)
Tried to see if fluorescent minerals would give off X-rays. Set some out in the sun with covered photographic film. If minerals gave of X-rays when they fluoresced, the film should darken – and it did.
Accidentally set some of these minerals in a dark drawer for a few days with undeveloped film, and was surprised to see the film strongly exposed. He knew they gave off X-rays when charged by the sun - but these results suggested the X-rays were coming from the mineral itself – Natural Radioactivity – No external energy source required!
Radioactivity
One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of
Marie Curie (1876-1934). She discovered radioactivity,
the spontaneous disintegration of some elements into smaller pieces.
Marie and Pierre Curie’s experiments with pitchblende – Discovered Radioactive Naturally occurring elements, particularly Uranium, Radium, and Polonium. Curium was named after Marie posthumously
THE GREAT DISCOVERY W.K. Roentgen’s experiment (1895) - Fluorescence –Certain substances will absorb photons of energy when exposed to a source (i.e. cathode rays, the sun), and then emit them over a period of time – thus they glow in dark when exposed to UV lightCathode rays –beams of electronsCathode ray tube (CRT) –Vacuum tube that has electric current passed through it .Component of television sets –that’s why they call it “the tube”
X-rays –Name given by Roentgen to unusual stray energy observed to cause fluorescence across the room when CRT was used… X-ray because he did not know what the heck it was….and the name stuck
BETA PARTICLES
•Consists of – high speed electron (from disintegration of neutron)
•Tissue damage potential – much greater than Alpha
•Harmful if ingested? – not as much as Alpha
•Can be blocked? – by glass, will penetrate skin
GOLD FOIL EXPERIMENTGOLD FOIL EXPERIMENTErnest Rutherford and the Gold Foil Experiment Ernest Rutherford and the Gold Foil Experiment
Disproved Thompson’s plum pudding modelDisproved Thompson’s plum pudding modelProved the existence of a nucleus with a positive charge Proved the existence of a nucleus with a positive charge
•Consists of – He nucleus•Tissue damage potential – great – if internalized•Harmful if ingested? – yup, very•Can be blocked? – by layer of skin, or cardboard
•Note that atoms are NOT conserved in nuclear reactions, but mass numbers and atomic numbers are.
ALPHA PARTICLES
NUCLEAR RADIATIONNUCLEAR RADIATION Ernest Rutherford and the Lead block experiment Ernest Rutherford and the Lead block experiment (1899) -(1899) - Alpha rays (Alpha rays ())Beta rays (Beta rays ()–)–Gamma rays (Gamma rays () )
How did Rutherford’s gold foil experiment change the theory of the structure of the atom?
Thompson1906
Rutherford1913
Bohr1924
ARCHITECTURE OF THE ATOM
•Atomic Number – Number of protons•Determine what type of element an atom is
•Mass Number – Sum of total number of protons and neutrons in an atom•Can change for an element depending upon the number of neutrons present
•Isotopes – Elements with the same atomic number, but different mass numbers
•Due to the difference in number of neutrons•Example:
•C-14 and C-12•H-1, H-2, and H-3
•Radioisotope – Isotope that is unstable and undergoes decay, thus giving off radiation
PARTICLE LOCATION CHARGE MASS
Protonnucleus
+1 amu
Neutron nucleus 0 1 amu
Electron Outside nucleus - 0.00054 amu
Subatomic Particles
Symbol Name Protons (Atomic Number)
Neutrons Mass Number
Electrons
73Li Lithium -7 3 4 7 3
146 C Carbon-14 6 8 14 6
6731Ga Gallium -67 31 36 67 31
Common Isotopes
Isotopes of Particular interest –C-14 used in radiocarbon dating I-131 used in thyroid cancer treatmentU-235 used in nuclear power
ISOTOPES IN NATURE
Atomic Mass -Weighted Average mass of all existing isotopes of an element
Can be calculated by: (percent isotope 1)(molar mass isotopes 1) + (percent isotopes 2)(molar mass isotope 2) +….. Try this with your grades as an example…. Final grades will be determined by giving homework 10%, labs 30%, and tests 60%…Homework grade = 85%Lab grade = 80%Test grade = 60% Final grade = (.10)(.85) + (.30)(.80) + (.60)(.60) = .69
Nuclear Section B Introduction
Approx. 90 known naturally occurring elements
Approx. 350 known isotopes in our solar system
Approx. 70 of these radioactive
Approx. 1,600 Lab created isotopes
Radioactive – just means unstable – it naturally decays
There is a rather constant level of natural radiation in our environment – called background radiation
Type Symbol Change in Atomic Number
Change in Neutrons
Change in Mass
NumberAlpha -2 -2 -4
Beta +1 -1 0
Gamma 0 0 0
TABLE OF CHANGES RESULTING FROM NUCLEAR DECAY
Spontaneous Radioactive Stability
1. Production of an particle
2. Production of a particle
3. Production of rays
4. Spontaneous Fission
1. production of particle
? He U 42
23892
Th He U 23490
42
23892
2. production of particle
? eTh 01
23490
Pa eTh 23491
01
23490
3. production of rays
?U*238
92
UU 23892
23892
*
4. Spontaneous Fission
DECAY SERIESShows the nuclear decay steps that occur when a radioactive isotope decays to a final stable product
II. Nuclear Fission
Sub-CriticalSub-Critical
CriticalCritical
SupercriticalSupercritical
then radioactive decomposition:
?? n β Kr 10
01-
9236
½ life = 1.3 sec
then radioactive decomposition:
½ life = 1.3 sec
Rb n β Kr 9137
10
01-
9236
then radioactive decomposition:
?? βBa 01-
14156
½ life 18.3 months
then radioactive decomposition:
½ life 18.3 months
La βBa 14157
01-
14156
Other Types of Nuclear Reactions
K-capture: the capture of an electron from the first or K shell
Other Types of Nuclear Reactions
Positron (0+1): a positive electron
207 207
Formation of a Neutron
An electron and proton combine to form a neutron.
0-1e + 1
1p --> 10n
fewer protons
more protons
Lessmass
III. Nuclear FusionExample #1
n He H H 10
42
31
21
Requires 40,000,000 K to Requires 40,000,000 K to
overcome electrostatic repulsionovercome electrostatic repulsion
Half life Half life
SM x (1/2)SM x (1/2)nn = EM = EM
(1/2)(1/2)nn = EM / SM or EM / SM = (1/2) = EM / SM or EM / SM = (1/2)nn
n log (1/2) = log (EM / SM)n log (1/2) = log (EM / SM)
n = log (EM / SM) / log (1/2)n = log (EM / SM) / log (1/2)
n = t / tn = t / t1/2 life1/2 life
ln (N/Nln (N/Noo) = ln (1/2)) = ln (1/2)nn
ln (N/Nln (N/Noo) = - kt) = - kt
tt1/2life1/2life k = ln (1/2) = 0.693 k = ln (1/2) = 0.693
tt1/2life 1/2life = 0.693/k= 0.693/k
A = kNA = kN
thus, N/Not = - kN1
where N = amount [conc or counts]and k = rate constant
dN/dt = - kN
t
0
N
N
dtk N
dN
0
t0
NN |kt| N ln
0
ktN
Nln
0
0N ln-ktN ln
Half-life : time when
0N2
1N
21kt
N
N21
ln0
0
Half-life
k
2ln 2
1 t
k
1/2ln -2
1 t
Binding Energyenergy released
during degradation of a nucleus
E = mc2
Energy = mass x speed of light2
1 gram of mass = 9 x 1013 joules = amount of energy needed to power your house for 1,000 years
E = mc2
or E = c2m
where c = 3.00 x 108 m/sec
SOURCES OF EXPOSURE TO IONIZING RADIATION
Nuclear Fission: Splitting of an atom into 2 or more “daughter particles”If daughter particles are unstable, then they will be radioactive
Particle Accelerators
Fission Chain Reaction
Hydrogen bombs
Results of fission reactions
IONIZING RADIATION – HOW MUCH IS SAFE?
•Rem – Roentgen equivalent to man•1Rem = 1000 mRem•Does not matter what type of radiation it is, it still has the same ionizing effect on living tissue•1 mRem of exposure to radiation increases risk of cancer death by 1 in 4 million•Two things to consider:
•Radiation density•Radiation dose
RADIATION DAMAGE: NOW AND LATER
•Radiation damage to your body can occur in several ways:•Break apart essential molecules
•proteins (i.e. enzymes)•nucleic acids (i.e. DNA)
•Mutations•Kills cells•Mutates sperm/ova•Cancer
•Government recommends no greater than exposure to 500 mrem per year for general public
•Government recommends no greater than 5,000 mrem per year from the workplace
Table of Factors Effecting Biological Damage from Radiation
FactorFactor EffectEffect
DoseDose Increase in dose Increase in dose produces proportional produces proportional increase in riskincrease in risk
Exposure timeExposure time Spreading out over time Spreading out over time decreases riskdecreases risk
Area ExposedArea Exposed Larger area means Larger area means greater riskgreater risk
Tissue typeTissue type Rapidly dividing cells Rapidly dividing cells more susceptiblemore susceptible
Radiation effects by dosage
EXPOSURE TO RADIATION
•Exposure to radiation can come from:•Cosmic Rays•Radioisotopes in rocks, soil, water, air•Fallout from nuclear weapons testing•Air travel•Radioisotope release from nuclear power generation
•Government recommends no greater than exposure to ______________for general public
•Government recommends no greater than ___________ per year from the workplace
•Radon gas comes from: Gas released from earth (from Uranium decay
•Radon gas exposure can lead to: lung cancer
•___________% of lung cancer deaths are caused by radon exposure.
•___________% of households in the U.S. have higher than recommended radon levels.
RADON IN HOMES