Unit 4: Nuclear Chemistry

Radioactive

Generally caused when an atom is unstable

Nuclear stability

The larger (more massive) a nucleus is, the harder it is for it to stay together

Natural decay

When a nucleus is radioactive, it gives off decay particles and changes from one element to another

Other words for natural decay

natural transmutation

Band of stability

the location of stable nuclei on a neutron-vs.-proton plot

What atoms have at least one stable isotope

Atoms with an atomic number of 1 through 83

What atoms are more reactive

All isotopes of elements about 84-natural radioisotopes

Nuclei above the belt have

too many neutrons, stabilized by beta emission

Beta emission

emits electron

Nuclei below the belt have

too many protons, positron emission/electron capture

Nuclei that have p>84

both too many protons and neutrons-a-emission

A emission

Alpha-He 2/4

Natural radioactivity

Spontaneous disintegration of the nucleus of an atom with the emission of particles or energy

Modes of decay

Alpha, beta, gamma, neutrons

Alpha decay; symbol, charge, mass, penetration strength

a, 2, 4, Low (apple)

Beta decay; symbol, charge, mass, penetration strength

B, -1, 0, moderate

Gamma decay; symbol, charge, mass, penetration strength

y, 0, 0, High

Neutrons decay; symbol, charge, mass, penetration strength

n, 0, 1, moderate

Radioactive materials will continue to decay until

they reach a stable # (usually with atomic # less than 83)

Beta particles

Fast moving electrons-little mass, stops ~1 cm into body

In Beta Decay, the effect is that

a neutron is converted into a proton, ejecting an electron from the nucleus

There are no electrons

in the nucleus. The ejected electron is formed when energy released from the nucleus 'congeals' into mass (E=mc^2)

Gamma radiation

Consists of high-energy photons, can penetrate to internal organs

Gamma ray symbol

0/0 y

Gamma rays are emitted when

nucleons rearrange into a more stable configuration

Gamma rays often

accompanies other nuclear decays and DOES NOT change the identity of the nucleus on its own

Positron decay

Images

Positron

identical to an electron, except that it has a positive charge

Neutrino

massless, chargeless particle

Electron capture

Nucleus captures orbiting electron

Positron decay image

Imagee

Electron Capture image

Imagee

Transmutations

When a nucleus decays into a new and different nucleus (also called radioactive)

Penetration

How far into a material the radioactive particle will go

Physical Reaction-same

compound and mass, charge

Physical Reaction different

Phases (s->l)

Chemical Reaction same

Mass and number of same atoms, charge

Chemical Reactions different

Compounds

Nuclear Reaction same

mass and charge

Nuclear reaction different

Elements

Rate of radioactive decay

each radioisotope has a unique rate of decay-half-life

An isotope's half life is

independent of temp, pressure, and its state of chem combination

useful in radioactive dating

Half-life

The period of time that must go by for half of the nuclei in the sample to undergo decay

During a half-life period

half of the radioactive nuclei in a sample decays to a new, more stable nuclei

How to find half life

1.) divide total time by one half life, which is # of half lives

2.) Count arrows

artificial transmutation

"man made" reaction caused by hitting a nucleus with a high energy particle, such as a neutron or alpha particle

Why do you need high speed particles in artificial transmutation

Alpha particle and nucleus are both positive, so they will repel each other otherwise

Unique to natural decay

Single unstable reactant decays into a decay particle and new, more stable nucleus

Common to natural transmutation and artificial transmutatiob

Mass and charge are conserves, both form new elements and produce energy

Unique to artificial transmutation

Stable nucleus and particle bullet collide to produce new products

Both natural transmutation and artificial transmutation produce

energy but natural decay produces less

Fission

Splitting of a nucleus into smaller nuclei, accompanied by a release of neutrons and large amount of energy (exothermic)

What elements are used in fission

Commonly used isotopes are Uranium-235 and Plutonium-239

Example of Fission Formula

235/92 U + 1/0 n->92/36 Kr +141/56 Ba +3 1/0 n + Energy

Fission photo

YAy

E=mc^2

Einstein's equation proposing that energy has mass; E is energy, m is mass, and c is the speed of light

In chemical equations, mass change is

nearly undetectable

The mass of the nucleus

less than the sum of the masses of its individual nucleons

Mass Defect

Mass of the constituent (nucleons)-mass of the nucleus

In mass defect, the missing mass is

converted into energy, which is used to hold the nucleus together-tighter, lighter separate, heavier

Fission requires

slow-moving neutrons

Important fissionable nuclei

U-233, U-235, Pu-239

Chain Reaction

One nuclear reaction leads to one or more others

Mass defect is also known as

mass deficiency

How does fission occur

Distance too big; strong force weakens, +/+ repulsion takes over, released n, free to split more nuclei

Control rods are commonly made of

boron or cadmium, and can be lowered into the reactor

Control rods

Slow the reaction by absorbing neutrons, so there is less available to trigger fission, stopping chain rxn

Moderators are usually

water, graphite

Moderators

help slow neutrons down in the reactor so that they can be absorbed by uranium atoms

Critical mass

the mass of fissionable material required to maintain a chain reaction at a constant rate

Supercritical Mass

the mass above which the chain reaction accelerates

Supercritical mass is used in

bombs

Benefits of nuclear energy

1.) No air pollution

2.) Small volume of material consumed

3.) Breeder reactors

Breeder reactors

Reactors that generate new fissionable material at a greater rate than the original fuel is consumed

Example of breeder reactors

U-238 to Pu-239 (Non fissionable transmutated to fissionable.)

Problems with nuclear energy

Nuclear waste (storage and transport)

Fusion

occurs when nuclei combine to produce a nucleus of greater mass

Fusion is known as a

exothermic process (much more energy than fission_

Example of fusion equation

3/1H+2/1H->4/2He+1/0n+Energy

Fusion equations have

smaller isotopes, always hydrogen

Artificial transmutation equations

Any other element besides ones typically used-not get energy

Fusion is also called

thermonuclear reactions

Products of fusion

generally not radioactive

Fusion requires

very high temperatures

Fusion currently

has not reached ignition, meaning, it requires more energy than it produces

Tokamaks

Use magnetic fields to contain and heat the plasma reactives

Dating

Carbon-14 is measured in dead organisms to find out when it was last alive based on its half life

medical

certain radioisotopes are useful because they contain short half lives and are quickly removed from the body

Iodine-131

Used to detect and treat thyroid disorders

Cobalt-60

emits gamma rays and is used to treat cancer-prostrate

Technetium-99

Detects cancerous brain tumors

Fusion formulas have

only hydrogen, produce helium

Fission formula

large creates large, neutrons on products side