chemistry 1 chemistry 1 nuclear chemistry chapter 28
TRANSCRIPT
CHEMISTRY 1Nuclear Chemistry
Chapter 28
NUCLEAR CHEMISTRY
1896- Antoine Becquerel discovered ___________________
He accidently left uranium ore on top of photographic plates. They became fogged from the exposure. Becquerel had 2 graduate students: _______________ _______________
radioactivity
Marie &Pierre Curie
_______________________- the property by which uranium gives off rays
______________________-penetrating rays emitted by a radioactive source.
In 1903, the Curies and Becquerel won Nobel prizes for this discovery.
Radioactivity
Radiation
Types of Radiation 1. Alpha emission -helium nuclei emitted from a
radioactive source 2 protons & 2 neutrons 2+ charge Symbol is Don’t travel far and are not very penetrating Stopped by a sheet of paper Can’t penetrate skin, but dangerous if ingested Very common with heavy nuclides
2
4He
Write this
Alpha Decay (α)
Lose 2 protons (+2 charge) & 2 neutrons
He42
Examples:
U ___ + He234
904
2
Ra Rn + He 2
4
88
226 222
86
23892 Th
Law of conservation of mass
Atomic #
Mass # = # protons + # neutrons
226 88
42
222 86
Ra Rn + He
Atomic # 88 86 + 2
Mass # 226 222 + 4
2. Beta emission - fast moving ___________ formed by the decomposition of a neutron of an atom. The neutron breaks into a proton and an electron. The proton stays in the nucleus and the electron is ejected. (net effect: neutron changes into proton) Write this:
n H + e0
1 1
1 1
0
electrons
Much smaller than alpha particles Symbol is Charge is -1 Much more penetrating than alpha particles Stopped by aluminum foil or thin pieces of
wood
1
0
C N + e 6
14
7
14
1
0
e
Write this
Beta Decay (β)
Lose electron (-1 charge, no mass)
β 0-1
C N + β14 6
14 7
0-1
3. Gamma emission - _________________ _____________ (high energy) emitted from a nucleus as it changes from an excited state to a ground energy state. Often emitted along with or radiation Symbol is Has no mass & no charge High energy photon
U He + Th + 2 92
238 4
2
234
90
electromagneticradiation
the emission of gamma rays is one way that a nucleus with excess energy (in an excited nuclear state) can relax to its ground state
Extremely penetrating, very dangerous Stopped somewhat by several feet of concrete or
several inches of lead
Gamma Emission (γ)
γ00
No mass, no charge, loses just energy
4. Positron emission- ___________________________________ e Antimatter Net effect: changes proton to a neutron Occurs when neutron/proton ratio is too small
10
22
0
1
0
1 Na e + Ne 11
22
Particle with the mass of an electron but a positive charge
Write this (the 0 and the +1)
Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper, but is dangerous in the lung.
Beta radiation can penetrate into the body but can be blocked out by a sheet of aluminum foil.
Gamma radiation can go right through the body and requires several centimeters of lead or concrete, or a meter or so of water, to block it.
Make sure you have both of these things: Calculator Periodic Table
Nuclear Transformation (Transmutation)- ____________________________________ bombarding with alpha particles
Bombarding with neutrons
N + He O + H 14
7
4
2
17
8
1
1
U + n U 238
92
1
0
239
92
Changing one element into another
Write these
Fill in the blanks (not in your notes):
1. Co Ni + ____
2. Am Np + ____
3. Th He + ____
4. N + ____ C + H
6027
6026
0 1
241 95
237 93
42
11
14 6
14 7
230 90
42
226 88 Ra
10 n
He
e
Half-life (t1/2)
the time required for ½ of the atoms of a radioisotope to emit radiation and decay to products
the longer the half-life, the more _____________ the isotope
varies from fractions of a second to millions of years
stable
Examples Nitrogen-13 decays to carbon-13 with a half-
life of 10 minutes. How long is 4 half lives?
4 half lives X 10 min/half life =
40 min.
If you start with 2.00 g of nitrogen-13 how many grams will remain after 4 half lives?
2.00 g 1.00 g 0.500 g 0.250 g
0.125 g
4
321
Phosphorous-32 has a half-life of 14.3 yr. How many grams remain after 57.2 yr from a 4.0 g sample?
57.2 yr
14.3yr / half-life= 4 half-lives
4.0 g 2.0 g 1.0 g 0.50 g321
0.25 g4
Carbon-14 dating
Carbon-14 is continuously produced in the ____________ when high energy neutrons from outer space collide with nitrogen-14 in the air.
N + n C + H 14
7
1
0
14
6
1
1
atmosphere
Carbon-14 combines with oxygen to form CO2 which is incorporated into plant materials. As long as the plant or animal is alive, decaying carbon-14 is continuously replaced. After death, the carbon-14 decays at a steady rate. Carbon-14 decays to Nitrogen-14
C e + N 14
6
0
114
7
The proportion of carbon-14 in the atmosphere is relatively constant. The carbon-14/carbon-12 ratio is used to identify the age of wood, cloth and other ______________ artifacts. The half-life of carbon-14 is _______________ years.
Only works for organic materials Adjusted for change in % C-14 over the years
organic5730
Example
If the C-14 in a fossil sample is only 1/4 what it is in living organisms, how old is the object?
To have ¼ remaining, 2 half lives have passed.
2 X 5730 yr =
11,460 yr.
Fission - splitting a heavy nucleus into two nuclei with smaller mass numbers.
used for _____________________
production of ______________causes a chain reaction (which must be controlled)
1 kg of uranium-235 is equivalent to 20,000 tons of dynamite
nuclear energy
n + U Ba + Kr + 3 n 1
0
235
92
142
56
91
361
0
neutrons
Fission – splitting of atoms.FISSION: splitting of atoms
Fission in a nuclear reactor is carefully controlled. Much of the energy is _______. This energy is used to produce _________ and subsequently, __________________.
A _________________(usually water) is needed. The water (or carbon) also acts as a moderator. It
_____________the neutrons down so that they can be captured by the U-235 fuel.
Control rods made of _______________ are present to absorb excess neutrons to slow down the reaction. They can be raised or lowered into the reactor core.
heatsteam
electricitycoolant
slows
cadmium
Fusion- combining two light nuclei to form a heavier, more stable nucleus
stars produce their energy this way Currently __________________ are
necessary in order to initiate fusion possible future energy source
high temperatures
4 H + 2e He + energy 1
1
1
0
2
4
Fusion – two nuclei combine to form a heavier nucleus.
FUSION: two nuclei combine to form a heavier nuclei
Proton-proton chain reaction
Fusion reaction in our Sun’s core.
Proton-proton chain reaction