Review

Draw a model of each of the hydrogen isotopes-Hydrogen-1-Hydrogen-2-Hydrogen-3

REVIEW

Compare and contrast Carbon-12 and Carbon-13(Note both commonalities and differences)

REVIEW

Give the chemical notation for the following atoms.

a)Nitrogen-15b)Carbon-13c) A sodium cation with a charge of +1d)A sulfur anion with a charge of -2

Example:

REVIEW

A) A sample of silver is 30.72% Silver-107 and 69.28% Silver-108.What is its average atomic mass/weight?

Chemical vs. Nuclear Reactions

Chemical Reaction Nuclear Reaction

Chemical reactions involve interactions between outer (valence) electrons of atoms or compounds.

Nuclear reactions change the composition of the atom’s nucleus

Nuclear ReactionsMost atoms have a stable nucleus and the nucleus will not change

Unstable atoms can emit radiation

Radiation: the process of sending out energy in the form of light, heat, x-rays or nuclear particles

Nuclear StabilityMost atoms have a stable nucleus not radioactive

Protons are positively charged, and like charges repel.

Hmm…then why doesn’t the nucleus fly apart since all the protons are repelling each other???

Nuclear StabilityAnother force, called the strong nuclear force is holding the nucleus together.

Strong nuclear force = the force that helps to hold the nucleus together. It is different from forces we encounter in daily life

Nuclear StabilityStrong nuclear forces help to balance the electromagnetic repulsion that the positive protons experience.Electromagnetic forces and strong nuclear forces are constantly pitted against each other.

Nuclear StabilityStrong nuclear forces……help to hold the nucleus together act like glue in the nucleus

Nuclear StabilityElements 1-20 neutrons = protonsBeyond element 20 more neutrons needed in nucleus to glue nucleus togetherBeyond element 83 (bismuth) no number of neutrons sufficient to glue the nucleus together indefinitely

Nuclear Stability

There are “magic numbers” of protons and neutrons (2, 8, 20, 28, 50, and 82) that are stable

Atoms with even number of protons and neutrons tend to be stable.

Radioactive DecayRadioactive Decay: We will study 3 types of radioactive decay.

Radioactive Decay(alpha decay)

Alpha Decay

Radioactive Decay(beta decay)

Beta Decay

Radioactive Decay(gamma decay)

Radioactive Decay(gamma decay)

Beta decay

Alpha decay

23089Ac

23691Pa

21884Po

Answer Key

Some more practice…Copy down problem into composition

book. Work with a partner to complete.

How does this happen?!?

As you learned during the previous lecture…

It all deals with the forces inside the nucleus of an atom!

Remember that a nucleus is just made up of + protons and neutral neutrons.

Neutrons help hold the protons of the nucleus together, but another attractive force is also needed!

This is called the strong nuclear force, which acts between all nucleons.

The strong nuclear force decays over distance though, so a large nucleus is not as stable as a small one.

These result in radioactive elements, that lose protons over time.

Nuclear FissionWhen nuclei of certain isotopes (typically larger) are

bombarded with neutrons, they undergo FISSION, the splitting of the nucleus into smaller fragments.

When you do this, the strong nuclear forces keeping all the nucleons together are released as energy.

Nuclear FissionThere are only two fissionable isotopes.

Draw the symbols for each below its name.

Uranium-235 Plutonium-239

Fission of UraniumCan you write the equation for this reaction???

Fission of Uranium

Notice that there the same numbers of protons on each sideHOW MANY?

92And the same number of neutrons on each sideHOW MANY?

144

Nuclear Fission In a chain reaction some of the neutrons released react with other fissionable atoms, releasing more neutrons which react with still more fissionable atoms.

Nuclear Fission An atomic bomb is a device that starts an uncontrolled nuclear chain reaction.

To be used for energy, fission must be controlled so that energy is released more slowly.

Nuclear Fission & EnergyIf you multiplied 7 kilograms of Uranium by the speed of light squared, you get about 2.1 billion Joules of energy.

By comparison, a 60-watt light bulb produces 60 Joules of energy per second.

2.1 billion Joules is the amount of energy contained within a million gallons of gasoline.

What you should get out of this is that a baseball size of Uranium has a much energy as a 50 by 50 foot room full of gasoline!!

Nuclear Fusion Nuclear fusion can be thought of as the opposite

of nuclear fission, that is small nuclei combine to produce a nucleus with a greater mass.This releases much more energy that a fission reaction, but only happens above 40,000,000 ⁰C

Happens during life cycles of stars!In fact, elements 1-20 were formed this way.

Nuclear Fusion Write the formula for 4 hydrogen nuclei combining to

create one helium nucleus:The following example shows the end result of a complex series of reaction where 2 of the 4 hydrogen nuclei are transformed into 2 neutrons. Then other changes in the nucleiresults in the productionof both deuterium andtritium. These fuse andrelease a neutron, thuscreating Helium. It’s complicated!!