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 http://www.adaptivecurriculum.com/proxy/AC/TPlayer/v0.0.9/actplayer.jsp#

Chapter 25: Nuclear Chemistry 25.1 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.

He wondered if they also emitted X-rays. 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

an alpha particle (we use the symbol α) is positive Alpha Radiation- radiation deflected toward the negatively charged plate

contains 2 protons 2 neutrons and has a 2+ charge Alpha particle contains 2 protons 2 neutrons and has a 2+ charge Has 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 energy Ex.: Sun powered by a series of fusion reactions high 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 reactions b. detect diseases c. PET scans

PET scan (positron emission tomography)

Medical Uses of Radiation Diagnostic: 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.

Concerns Radioactive 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