Name ______

Chapter 22 Nuclear Chemistry

History – not in textbook from the nuclear engineering dept. at NCSU

1895x-rays discovered By Roentgen *1898 Curies*

1905E=mc2

1913Bohr model of atom *Quantum* perfect calculations for H atom

19191st nuclear Reaction

1932Neutron discovered by Chadwick

1934artificial radioactivity

1939Fission discovered by Lise Meitner (story in textbook)

19421st controlled chain Reaction

Enrico Fermi University of Chicago

Atomic pile; composed of Uranium & graphite

Manhattan Project  atom bomb

Oak Ridge, UC Berkeley with Dr. Oppenheimer

* U & Th then Po, Ra discovered

Note: Germans needed dry ice to do research on nuclear fusion (They said no to Nazis)

p.1

Chapter 22 Nucleus & Radioactivity p.701

Nuclear Chemistry

Mass  AProtons + Neutrons  14

Atomic #  Z Protons  6

Introduction:

Chemistry is determined by valence e- with a positive nucleus that keeps e- bound in atoms & compounds

Nucleus: very small, very dense

Nuclear Radius 10-13 cm vs. of atomic radius 10-8 cm

Distance

Size: can be related as…

Difference in distance between - Ping Pong Ball as the nucleus

and the furthest electron from the nucleus at 0.5km or 0.3mi which is about the length of a football field

Density- Nucleus is Very Dense

If 1.6 *1014 g/cm3were the density of a ping pong ball, it would weigh 2.5 billion tons

Energy

Nuclear Reaction yields 106 times more energy than any chemical Reaction

Originally Greek atom thought atoms to be indivisible, now know, e-, p and n and more recent subatomic particles include quarks (not studied here)

Nucleon(a particle in the nucleus can be either a n or p)

Nuclides are isotopes e.g.C-12C-13C-14

p.2

Nuclear Particles p. 706

p.713 protection and exposure

Alpha particle,

Beta particle, an electron,

Beta-plus particle, a positron (not studied here)

Neutron

Types of ParticlesSymbolNecessary Protection

alpha (helium nuclei) 42He air, paper

beta (electrons) 0-1e plastic, foil

gamma-radiation lead, concrete

p. 3
p.701 and 705 Radioactive Decay:

Smaller (more stable) atoms have P:N ratio of 1:1 more stable

Larger atoms (can be more unstable) have P:N ratio of 1:1.5, these are unstable and start to fall apart i.e. are radioactive.

Transmutation: identity changes because nucleus changes (i.e. the # Protons)

Nuclear Reactions nucleus changes

Nuclear equations must be balanced.

To balance nuclear equations, follow these rules:

  1. Mass number is conserved in a nuclear change.
  1. Electric charge is conserved in a nuclear change.

p.4

p. 705 Radioactive Decay (sometimes change mass # of an element but the total mass before and after the decay would be the same) do the sample problems on p. 704

1)Alpha Decay 42He – (α,nota)

Example:23892 U 42He + 23490Th

23090Th 42He + 22688Ra

2)Beta decay occurs when a neutron splits into a proton and an electron that leaves the nucleus (emitting an electron i.e. beta particle)

23490Th 23491Pa + 0-1e

13153I 13154Xe + 0-1e

3)Spontaneous Fission: split into 2 lighter nuclides

Some elements do not change mass, but do change atomic #

Neutron bombards the nuclide

U235929236Kr + 14156Ba + 3 neutrons

Neutron

p. 710 Radioactive Decay Series of radium 226

and the Fermi lab (1st controlled nuclear reaction -1942 enabled the making of the atom bomb) on p. 711

p.5

Fusion v.s. Fission p. 717

Fusion:

Deuterium 21H

+ 42He + neutron + ENERGY!!!!!!!

Tritium 31H

Fusion occurs naturally on the sun

Fusion can only occur in plasma.

Plasma: low density superheated gas

Example: Hydrogen Bombs

Fusion – occurs in sun and stars

4 11H 24He + 2 +10eenergy

When the 4 pieces fuse, energy is released.

p.6

Fission: split into more stable nuclei of intermediate mass occurs spontaneously or by neutron bombardment

U 235 + slow 01n  becomes unstable & splits

Fission:

U235929236Kr + 14156Ba + 3 neutrons + **Energy Released**

Example: Atomic Bomb

p.7
Nuclear Reactors have controlled fission chain Reactions to get Energy or Radioactive nuclides - Nuclear Power: stopped by cadmiumrods which absorbs neutrons

p. 718 Nuclear Power Plants Reaction  heat  hot H2O  electricity in turbines

U-235 used often

Shielding: absorb radiation especially with Cd rods which absorb neutrons or Lead shields stop radiation (does not pass through the lead shield)

Fuel: U-235

Control Rods- neutron absorbing

Moderator: slows fast neutron  to be slow

Coolant: H2O i.e. Cooling Towers like Shearon Harris plant in Apex

Nuclear Chemistry Uses p.715

  1. Power
  2. Medicine

a)PET scan

b)MRI

c)X-Rays

d)Tracers

e)Radiation Therapy

  1. Forensics: Hair, nails, As, gamma spectrometer at NCSU
  2. Toxic Metal Waste: Hg, Se
  3. Space: Nuclear Batteries

p.8

p. 714 Radiation Detection:

a)Film Badges

b)Geiger Counters

c)Scintillation Counters

Nuclear Waste :

  1. 103 Nuclear Reactors (power)
  2. Refuel every 12-24 months
  3. Some plants ship spent fuel
  4. By 2010, government said “replace power plant”
  5. **Yucca mntn*

Chernobyl: nuclear disaster in the Ukraine- released 7000 kg of radioactive decay. Damage was detected as far as Washington, DC.

Geiger Counter: an instrument used to measure the level of radiation.

Dosimeter: personal radiation device

Scientists make radioactive isotopes: can be used for….

a) Medicine

b)Radiation therapy for cancer uses

c)X-rays and Gamma Rays

(From Cobalt-60 and Cesium-137) & Research  P32 and S35

Tracers: radioactive isotopes, natural and manufactured. Chemical tracers follow certain metabolic processes in the body.

Irradiation: radioisotopes used to treat food so that it can be stored without refrigeration for a long time.

p. 9

Half Life p. 708 do problems on p. 709

Each radioactive element breaks down at a specific rate.

The time required for one half of a sample to decay is known as the half-life of that substance.

The half-life is constant regardless of what you do to that element.

Some elements decay to a stable nucleus in less than 1 second. Others may require millions of years.

Carbon-14 (isotope of carbon with neutrons)

It is found in all living things. It is absorbed in CO2. The half-life is 5730 years. By measuring the percentage of C-14 in a fossil or skeleton, scientists can determine the age of the material.

This is called radioactive dating.

p. 10

Half-life p. 708

Half-life: time required to decay ½

Example: ½ atoms to transform into something else

20g 10g 5g2.5g

Graphs:

No

½ No

¼ No

1/8 No

0t ½ 2t ½ 3t ½ 4t ½

No =original amount of substance

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