Chem Ch.21 (Nuclear Chemistry)

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Nuclear Reactions
Transformations of atomic nuclei that can involve enormous changes in energy. Roughly 13% of electricity worldwide comes from nuclear power plants.

i.e. Energy of stars and created by nuclear power plants. (908)

Table 21.1 (912), Table 21.3 (913), figure 21.15 (933), Table 21.9 (941)
Subatomic particles that reside in the nucleus, protons (+) and neutrons (0).

Atomic number = number of protons.
Mass number = protons (p) + neutrons (n)
Isotopes = atoms with same atomic number but different mass numbers (same protons, changing neutrons)
(910 – 911)

Radionuclides & Radioisotopes
Radionuclides: A nuclide, a nucleus containing a specified number of protons and neutrons, that is radioactive. Unstable and spontaneously emit particles and electromagnetic radiation.

Radioisotopes: The atoms containing these nuclei. (911)

Alpha (α) particles
helium-4 particles. A stream of these particles will cause alpha radiation.

Written as (4)(2)He

Alpha Decay
When a nucleus spontaneously decomposes. A type of radioactive decay that involves alpha particles. (911)
beta (β) partcles
β⁻ or (0)(-1)e

High speed electrons emitted by an unstable nucleus. Beta radiation occurs when a steady steam of beta particles is being emitted. (912)

beta emission
Basically beta decay because β⁻ subtracts one proton (subtracts atomic number by 1). (912)
Gamma (γ) radiation
Gamma rays. High energy photons (electroagnetic radiation of very short wavelength). It doesn’t change atomic or mass number. Typically accompanies another radioactive emission b/c it represents the energy lost when the nucleons in a nuclear reaction reorganize into more stable arrangements. (913)
Positron & Positron Emission
(0)(+1)e or β⁺ is a positron.

Positron emission will cause the atomic number to increase by +1. (913)

Electron Capture
The capture by the nucleus of an electron from the electron cloud surrounding the nucleus.

i.e. (81)(37)Rb + (0)(-1)e (orbital electron) → (81)(36) Kr


Neutron-to-Proton Ratio
1. High neutron to proton ratio can lower their ratio and become more stable by emitting a beta particle (beta emission).

2. Low neutron to proton ratio can increase their ratio by positron emission or electron capture.

3. Nuclei with atomic numbers 84+ can undergo heavy alpha emission, but otherwise all nuclei with 84+ protons will be radioactive.

(914 – 915)

Radioactive Decay Chain / Nuclear Disintegration Series
A series of nuclear reactions that begins with an unstable nucleus and terminates with a stable nucleus.

3 Occur in nature:
uranium-238 to lead-206
uranium-235 to lead-207
thorium-232 to lead-208

Magic numbers
The number of protons and neurons that will often have a more stable nuclei that those without these numbers.

1. Protons: 2,8 , 20, 28, 50, 82
2. Neutrons: 2, 8, 20, 28, 50, 82, 126
3. Nuclei with even number of p, n, or both.

Nuclear transmutations
A nucleus that is struck by a neutron or by another nucleus. (918)
Particle Accelerators
“Atom smashers.” Used to move bombarding particles faster. The charged particle will be manipulated by electric and magnetic fields. (919)
Transuranium Elements
Elements with the atomic number 93 and up. Nuclear transmutations were used to create these. (920)
Half Life
Radioactive decay is first-order kinetic process. Half life is the time required for half of any given quantity of a substance to react. Unaffected by exernal conditions. (921)
Half Life Equation
Rate = kN

k = decay constant (first order rate constant)
N = number of radioactive nuclei


Activity & Becquirel (Bq) & Curie (Ci)
Activity is the rate at which a sample decays.

The becquerel (Bq) is the SI unit for expressing activity. It is (1 nuclear disintegration/second).

The curie (Ci) is 3.7*10¹⁰ disintegrations/second. Unit of activity. Same rate of decay at 1 g of radium.

First-Order Rate Law
ln (Nt/N0) = -kt

t = time interval of decay
k = decay constant
N0 = initial umber of nuclei at time zero
Nt = number of remaining nuclei after time interval.

k = 0.693 / t

Element’s oath is revealed by the radioactivity of the radiosotope (which is also a radiotracer)
Energy Changes in Nuclear Reactions
E = mc^2

Mass and energy are equivalent and can be converted into one another. If a system loses mass, it loses energy and vice versa.

Mass defect
The mass difference between a nucleus and it’s constituent nucleons.
Nuclear binding energy
The energy required to separate a nucleus into its individual nucleons. (931)
Heavy nuclei gain stability and therefore give off energy. The energy is used to generate energy in Nuclear power plants. (931)
This process is when small mass numbers give off more energy than if nuclei were combined together. This is an essential energy producing process in the sun and other stars. (931)
Chain reactions
A heavy nuclei splits as a fusion. If one fission produces 2 neutrons,those 2 can produce 2 additional goals with 2 neutrons each, having four total. Those 4 can produce 4 more fissions, etc. Can result in violent explosion if left unchecked. (932)
Critical mass
The amount of fisionable material large enough to maintain a chain reaction with a constant rate of fission. When critical mass is hit, fusion will slow to a controllable rate.
Supercritical mass
If more than a critical mass of fisionable material is present, very few neutrons escape. The chain reaction multiples more and can lead to a nuclear explosion. A mass in excess of a critical mass is supercritical mass. (933)
Nuclear reactors
Fuel elements contain enriched uranium in tubes. The control rods absorb neutrons, the rods regulate the Flux of neutrons and prevent the core reactor from overheating. The moderator slows neutrons. The primary coolant transports heart generated by the nuclear chain reaction away from the core. (935)
How to get rid of nuclear waste?
Fast breeder reactor, turn waste into glass, stone, ceramic to immobilize it (937)
Thermo nuclear reactions
In order for two nuclei to fuse, there needs to be extremely high temperatures and pressure. The lowest temperature for fusion is 40,000,000 K. (937)
Ionizing radiation
When matter absorbs radiation, the radiation energy causes atoms in the matter to be excited or ionized. Radiation that causes ionization is ionizing radiation. More harmful to biological systems than radiation that does not cause ionization. (938)
Nonionizing Radiation
Radiation that does not cause ionization. Lower in energy. (938)
Free Radical
When ionizing radiation passes through living tissue, electrons are removed from water molecules to form highly reactive H₂O⁺ ions and it will react with more water to form H₃O⁺ and OH.

H₂O⁺ + H₂O → H₃O⁺ + OH

The unstable and highly reactive OH molecule is the FREE RADICAL, a substance wit one or more unpaired electrons.

OH molecule is also called as hydroxyl radical. Hydroxyl radicals can attack more biomolecules to produce new free radicals. (939 – 940)

Gray (Gy) & rad (Radiation Adsorbed Dose)
Gy is SI unit for absorbed dose; 1J/kg of tissue

rad is 1*10⁻² J/kg of tissue

1 Gy = 100 rad

Relative Biological Effectivess (RBE)
Radiation doze multiplied by a factor that measures the relative damage caused by radiation.

RBE = 1 gamma, 1 beta, 10 alpha

REM (Roentgen Equivalent for Man)
Effective dosage in REM (Roentgen Equivalent for Man) is the product of radiation dose and the RBE of radiation.

# of rem = (# of rad)(RBE)

SI unit is sievert (Sv) = RBE * Gy
1 Sv = 100 rem

A product of the nuclear disintegration of series of uranium-238 and is continuously generated as uranium in rocks and soil decays.
Categories: Nuclear Chemistry