Unit 5 The Structure of Matter

Chapter 16 The Atom

16C – The Nuclear Atom• Objectives:

– Define radioactivity and identify important kinds of nuclear radiation

– Describe the various processes of nuclear decay and how each affects the atom

– Use nuclear decay equations to illustrate each kind of decay process

– Discuss one application of nuclear decay t hat helps save lives

– Compare and contrast nuclear fission and fusion, including the conditions under which each occurs

– Discuss the difficulties of developing electrical generation using fusion energy

• Assignments: Outline, Worksheet and Section Review page 405

Nuclear Radiation• Antoine Henri Becquerel

– French physicist who discovered nuclear radiation and radioactivity

– Won Nobel Prize in Physics• Too many or too few neutrons in an atom leads

to less stability• Nuclear Chemistry

– The study of changes that occur in the atomic nuclei– Began by the accidental discovery of radioactivity

• The emission of nuclear radiation– Rays and particle emitted by unstable nuclei

• Experiments led to the discovery of alpha particles, beta particles, and gamma rays– symbolized by the Greek letters

Nuclear Decay• Larger nucleus = excess energy• Gamma Decay– No change in the atom except for

reducing the amount of energy in its nucleus

– Can be very damaging to organic molecules found in living things

– Molecules that absorb gamma rays can be destroyed as the energy disrupts bond between atoms

Alpha Decay• More significant then gamma• Loses an alpha particle, equal to helium

– Atom’s nucleus loses two protons and two neutrons, reducing its atomic number by 2 and its mass number by 4

• Because its atomic number has changed, the atom is now an isotope of a DIFFERENT element

• Once the alpha particle hits something it gains electrons and becomes a normal helium atom; however it tends to interact with other atoms very easily, damaging chemical bonds as it rips electrons away from other atoms and molecules

Beta Decay• Ratio of protons and neutrons is too

large to be stable• A neutron changes to a proton• Emits a beta particle, a high energy

electron• The mass number stays the same• The atomic number increases by one

changing the atom into an isotope of another element

Decay Equations

What Can Stop Radiation?

Nuclear Bombardment Reactions

• Happens when a nucleus is struck by a high energy particle or another nucleus

• Different than nuclear decay because bombardment reactions release millions of times more energy and many more particles than alpha or beta decay

• Almost always artificially induced in special nuclear reactions and particle accelerators

Nuclear Fission• Occurs when a large, unstable nucleus splits into

smaller, more stable nuclei, releasing energy• Forced to occur artificially in a nuclear reactor• Can also occur spontaneously, although rare• As neutrons are released they are absorbed by

other nuclei which also fission releasing more free neutrons causing a chain reaction

• In a controlled nuclear chain reaction an immense amount of energy can be release to do useful work

• Fission bombs are better known as atomic bombs or nuclear bombs

Nuclear Fusion

• The opposite of fission• Smashing smaller nuclei together to

form a large one• Produces even more energy than

fission• Fusion bombs, better known as

hydrogen bombs or thermonuclear bombs