Nuclear Chemistry

Isotopes

When an atom or element can be found somewhere on Earth, it is called naturally occurring.

Of the 118 elements on the periodic table, 92 are naturally occurring; the rest exist only as a result of human activity or unusual circumstances.

Some elements have only one isotope, but most have more than one.

Stable vs. Radioactive IsotopesRadioactive Isotopes

Not stable

Emit small particles (neutrons, protons, electrons, and odd mixes or variations of these particles).

Called radioactive isotopes.

not common; the majority of radioactive isotopes are elements with atomic numbers above 80.

Stable isotopes

have a stable nucleus. Stable = balance between the

number of protons and neutrons in a nucleus

Too few or too many neutrons will lead to the disintegration of an atom.

The larger the atom, the more neutrons it takes to make a stable nucleus.

What is radiation????

Why are some substances radioactive?

Nuclear Chemistry

Radiation: particles emitted from the nucleus

Substances are radioactive because the neutron to proton ratio is “off”

Radioactive substances emit radiation in order to get at n0: p+ ratio that is stable (low energy)

Band of Stability

Nuclear Radiation

Radioactivity: particles or radiation emitted from a nucleus during radioactive decay

Radioactive Decay: the spontaneous break-down of a nucleus into a slightly lighter nucleus, accompanied by the emission of nuclear radiation

Types of Nuclear Radiation

1. alpha particles

2. beta particles

3. gamma rays

Ionizing Radiation: can ionize atoms that they hit

Emission of these types of particles (nuclear reactions) involve changes to the nucleus of the atom!

Alpha Radiation (α)

2 protons & 2 neutrons bound together.

Nucleus of a helium atom

Symbol 42He

Particles do not travel far and are not very penetrating

Particles can be stopped by a piece of paper!

U238 92 Th + He234

90 4 2

Beta Radiation (β) An electron that has been ejected from the

nucleus Formed when a neutron breaks down into a

proton and electron Has a charge of -1 Mass 1/1837 amu

Symbol: 0-1e or β

Can pass through paper,

but not aluminum foil

or wood

C N + e14 6

0 -1

14 7

Gamma Radiation (γ) high-energy photon emitted by a radioisotope is

a gamma ray (). often emitted along with alpha or beta particles

during radioactive decay. have no mass and no electrical charge. extremely penetrating; can be stopped, although

not completely, by several centimeters of lead.

In your notebook.....

1. Sketch the picture below

2. Identify the type of radiation being depicted.

AB

C

In your notebook.....

1. Sketch the picture below

2. Identify the type of radiation being depicted.

Balancing Nuclear Equations

- follows law of Conservation of Mass

-mass numbers for products and reactants have to equal.

-atomic numbers for products and reactants have to equal.

37+0 = 37

20+ -1 = 19

Balance the following nuclear equations by adding the correct particle, and complete the sentence

(copy these into your notebook!)

Uranium-235 undergoes _____________ decay

Radium 226 undergoes _____________ decay

Technecium-99 undergoes _____________ decay

Writing nuclear equations

Write a balanced nuclear reaction for the following:

1. Potassium-37 undergoes beta decay.

2. Polonium-210 undergoes alpha decay.

Half LifeIs the time required for one-half of a sample to decay (really, to change

into another element).

For example, it takes 5730 years for half of a sample of carbon-14 to decay into nitrogen-14 through beta decay.

Calculate Half Life

AF = AI * (.5) t/h

Final Amount Initial

Amount

Time

Half-Life

Give it a try

An isotope of cesium (cesium-137) has a half-life of 30 years. If 1.0 mg of cesium-137 disintegrates over a period of 90 years, how many mg of cesium-137 would remain?

Fission & Fusion

Fusion

Fusion: when two small nuclei combine to form a larger more stable nucleus

Ex.: energy from the sun comes from nuclear fusion

Fission

Fission: a large nucleus splits apart into lighter more stable nuclei

Ex.: type of reaction that occurs in a nuclear reactor