Chapter 4 & 25 Nuclear Chemistry

• Chapter 4 &25 Nuclear Chemistry

4.4 Unstable Nuclei and Radioactive Decay

Chemical reactions involve only electrons, NOT the nucleus.

Protons determine the identity of an atom.

Change the protons, it is a different atom!!

4.4 Unstable Nuclei and Radioactive Decay

Nuclear Reactions- reactions which involve a change in an atom’s nucleus

Radioactivity- substances spontaneously emit radiation

Radiation- rays and particles emitted by the radioactive material

By emitting radiation, atoms of one element can change into atoms of another element.

Radioactive atoms

Emit radiation because their nuclei are unstable.

Radioactive decay- a spontaneous process in which unstable nuclei lose energy by emitting radiation

Unstable radioactive atoms undergo radioactive decay until they form stable non radioactive atoms of a different element.

History of Radioactivity

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Chapter 25: Nuclear Chemistry25.1 Nuclear Radiation

1895- William Roentgen; discovered x-rays (form of high-energy electromagnetic radiation)rays caused photographic

plates to darken

He took “pictures” of his wife’s hand.rays caused

photographic plates to darken

In 1901 Röntgen was awarded the very first Nobel Prize in Physics.

Henri Becquerel

1896 - studied minerals that emit light after being exposed to sunlight- called phosphorescence.

He wondered if they also emitted X-rays.

Accidentally, he discovered uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material.

Later, Becquerel demonstrated that the radiation shared certain characteristics with X rays but, unlike X rays, radiation could be deflected by a magnetic field and therefore must consist of charged particles.

For his discovery of radioactivity, Becquerel was awarded the 1903 Nobel Prize for physics.

The Curies Marie Curie and Pierre Curie took

Becquerel’s mineral and isolated components;

found that rays were being emitted by Uranium

they called this process radioactivity Marie discovered that the uranium

nucleus is radioactive Becquerel & Curies shared Nobel prize

for their work

1898 - Marie and Pierre Curie – isolated the elements that were emitting the rays.

polonium, and radium

Rate of radioactive emission of charged particles from elements could be measured and compared.

In addition, she found that there was a decrease in the rate of radioactive emissions over time and that this decrease could be calculated and predicted.

But perhaps Marie Curie's greatest and most unique achievement was her realization that radiation is an atomic property of matter.

Nobel Prize in Physics 1903 – was shared; Curies and Becquerel for work in radioactivity

Nobel Prize in Chemistry 1911 – Marie Curie for her work with the elements Polonium and Radium.

3 Types of Radiation

1800’s Scientists directed radiation between 2 electrically charged plates and found there were 3 different types; some deflected to the negative, some to the positive, and some were not deflected at all.

Types of Radiation

Radioisotopes- isotopes of atoms with unstable nuclei

C-14 is a radioisotope of C-12 Most common types of

radiation are alpha, beta, and gamma rays

Experiment

Alpha Particle

an alpha particle (we use the symbol α) is positive

Alpha Radiation- radiation deflected toward the negatively charged plate

Alpha particle

contains 2 protons 2 neutrons and has a 2+ chargeHas a mass number of 4

Alpha Radiation

Positive charge is why it is attracted to negative plate

Equivalent to helium-4 nucleus

Ex:

Beta Radiation

a beta particle (symbol β) is negative

Beta Radiation- radiation that was deflected towards the positively charged plate

Beta Particles- radiation consisting of fast moving electrons

Beta particles consist of an electron with a 1- charge

Ex:

Beta Particles

A neutron becomes a proton and an electron. The electron leaves the atom at high speed.

What blocks these rays!

Gamma Radiation

a gamma ray (symbol γ) is neutral

Gamma Rays- high-energy radiation that possesses no mass and no charge

Usually accompany alpha and beta radiation

Accounts for most of the energy lost during radioactive decay

Gamma rays cannot result in the formation of a new atom

Ex:

What blocks these rays!

Practice worksheet

25.4 Fission and Fusion of Atomic Nuclei

Nuclear Fission- the splitting of a nucleus into fragments; accompanied by a very large release of energy

During fission, a neutron collides into an unstable nucleus causing a chain reaction

The neutrons released can cause more fissions, which releases more neutrons causing more fissions and so on.

Chain reaction – self-sustaining process in which one reaction initiates the next.

Critical mass – a sample that is massive enough to sustain a chain reaction.

More than a critical mass can generate a nuclear explosion.

Nuclear Fission Reaction

Heavier isotopes is broken down into lighter isotopes

Uses of Fission

Nuclear Power plants Building of the A-bomb

Fusion

Nuclear Fusion- the combining of atomic nuclei; capable of releasing large amounts of energyEx.: Sun powered by a series of

fusion reactionshigh amount of energy is

required to create reaction

Fusion Equation

25.5 Applications and Effects of Nuclear Reactions

Ionizing radiation - radiation energetic enough to ionize (damage) matter with which it collides.

Detected by Geiger counters

Uses of Radiation

Radiotracer - radioisotope that emits non-ionizing radiation and is used to signal the presence of an element or specific substance.a. analyze reactionsb. detect diseasesc. PET scans

PET scan (positron emission tomography)

Medical Uses of RadiationDiagnostic: Radiotracers such

as technitium-99 can be injected in the blood stream and then tracked through the body to see if organs are functioning properly; also can help diagnose cancer (PET scan)

Therapy: Radiation treatments can kill the cancer cells in cancer patients

Commercial applications

Smoke detectors: have a tiny mass of americium-241, which is a source of alpha radiation

Rifle sights: tritium is used with phosphor to increase nighttime firing accuracy

Exit signs: luminescence is due to a small amount of radioactivity

Food irradiation: exposing food to ionizing radiation to destroy microorganisms, bacteria, viruses, and insects

X-Rays

X-rays and gamma rays – high-energy electromagnetic radiation that is extremely penetrating and damaging to living tissue.

Blocked by lead and concrete.

Radiochemical Dating

The half-life of any radioisotope is constant

Radiochemical dating – process of determining the age of an object by measuring the amount of a certain radioisotope remaining in that object.

ConcernsRadioactive materials have

long half-lives and continue to be damaging for many years

No good way to dispose of nuclear waste because it can contaminate water, soil, and air