NUCLEAR CHEMISTRYChapter 10

Chemical Rxn vs. Nuclear Rxn• Chemical reactions involve valence ELECTRONS

• Nuclear reactions involve PROTONS and NEUTRONS

Chemical Energy• Energy stored in the chemical bonds of a substance

• Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products• During this process, energy is either released (exothermic) or

absorbed (endothermic)

Radioactivity• The process in which an unstable atomic nucleus emits

charged particles and energy

• An atom that has an unstable nucleus is called a Radioactive isotope, or Radioisotope

• Carbon-14 is an example of a radioisotope

• Radioisotopes spontaneously change in to other isotopes over time• This is called NUCLEAR DECAY and can result in the formation of

an entirely different element than the original element

Historical Figures Jigsaw• What important discovery was made by Wilhelm Roentgen?

• What material did Antoine Becquerel work with in his own investigations of X rays?

• What did Becquerel discover through his experiments?

• What two elements were discovered by Marie and Pierre Curie?

• Why is Ernest Rutherford considered the father of nuclear physics? List Rutherford's major achievements.

Radioactivity (The Good, The Bad)• Safari Montage

Nuclear Force• The attractive force that binds protons and neutrons

together in the nucleus

• Extremely weak at most distances, BUT over the very short distances present in an atom’s nucleus, the nuclear force is greater than the repulsive electrical force among protons

• When the attractive nuclear force and the repulsive electrical force are not balanced, the nucleus of the atom is UNSTABLE

How does a nucleus become stable?• Through radioactive (or nuclear) decay!

• Radiation is emitted from the unstable nucleus in the form of fast-moving particles and energy

• This results in new nucleus and thus the identity of the element changes

• Atoms that have an unstable nucleus are called radioactive isotopes

Nuclear Radiation• Charged particles and energy that are emitted from the

nuclei of a radioactive isotope

• Types• Alpha Particles – Least penetrating, travel only a few centimeters

in air, can be stopped by clothes or a sheet of paper• Beta Particles – More penetrating than alpha particles, pass

through paper, stopped by thin sheet of metal• Gamma Radiation – Much more penetrating than alpha and beta

particles, need several centimeters of lead or several meters of concrete to stop gamma radiation

Alpha Decay• Alpha Particle

• Positively charged particle made up of two protons and two neutrons

• Has a charge of +2• QUESTION: If an alpha particle has two protons, which element

does is resemble?

Alpha Decay • Alpha particles are represented by

• This type of nuclear reaction can be expressed as an equation (write in the parts of the equation below):

Beta Particles• An electron emitted by an unstable nucleus

• Has a mass number of (0) and a charge of (-1)

Beta Decay• During Beta Decay, ONE neutron decays into ONE proton

and ONE electron• The PROTON stays trapped in the nucleus and the ELECTRON is

released

• What does this mean?• The product isotope has ONE proton more and one neutron fewer

than the reactant isotope, but the mass numbers are the same because electrons have NO mass.

Gamma Radiation• A penetrating ray of energy emitted by an unstable

nucleus

• Has no mass and no charge

• Travel through space at the speed of light

• Can easily pass through the human body

Ionizations• The process of stripping, knocking off or otherwise

removing electrons from their orbital paths

• This creates free negatively-charged electrons and leaves nuclei that have a positive charge

• These particles can interact with other materials to produce changes in materials (like our body)• If this happens in our cells, cellular damage may result

Nuclear Power• How it Works

• Chernobyl Disaster

Sources of Radiation• Background Radiation

• Nuclear radiation that occurs naturally in the environment• Examples: Air, water, rocks, plants, animals, cosmic rays• Cosmic rays

• Streams of charged particles from outer space

• Nuclear Radiation in the body• Because particles and energy can ionize cells in the human body, they can

break apart the bonds holding DNA and proteins together• If these molecules change, cells may no longer function how they are supposed to

• Radon Gas• Emits alpha particles, can cause lung cancer• Formed through a series of nuclear decays that begins with uranium-238 deep

underground• Radon gas seeps upwards and can accumulate in basements that don’t have

proper ventilation

Geiger Counters• Used to detect nuclear radiation

• Uses a gas-filled tube to measure ionizing radiation

• Nuclear radiation enters tube, the gas in the tube is ionized and generates an electric current, which can be measured

• More nuclear radiation = greater electrical current

Group Discussion• What is nuclear decay?

• What is emitted from a radioactive isotope during radioactive decay?

Half-life• Nuclear Decay Rate

• Refers to how fast nuclear changes take place in a radioactive substance

• Constant for a given radioactive isotope

• The length of time necessary for half of the atoms of a sample material to decay• Half of the atoms have decayed, half remain the same

• Range from fractions of a second to billions of years for long-lived materials

Radiocarbon Dating• http://www.youtube.com/watch?v=phZeE7Att_s

• The age of an object is determined by comparing the object’s carbon-14 levels with carbon-14 levels in the atmosphere

• Used to date fossils up to 50,000 years old

• Why does this work?• Plants absorb carbon dioxide from the atmosphere during photosynthesis• While alive, they maintain the same ratio of Carbon-14 to Carbon 12 as in

the atmosphere• Animals have the same ratio of C-14 to C-12 as the plants they eat• Once a plant or animal dies, it no longer absorbs carbon and so the

remaining C-14 begins to decay