Chemistry - Chapter 22:  The Nucleus

I.  Subatomic particles

    A.  Leptons (6):  elementary particles;  have no internal structure;  do not respond to the strong nuclear force;

    B.  Hadrons:  not an elementary particle;  have internal structure;  does respond to the strong nuclear force;  made of quarks

        1.  quarks (6):  elementary particles;  have no internal structure;  responds to the strong nuclear force

                a.  "flavors":  types of quarks;  each "flavor" is charged;  there are three pairs of quarks

                        1.  up and down:  up = +2/3;  down = -1/3

                        2.  strange and charm:  charm = +2/3;  strange = -1/3

                        3.  top and bottom (or truth and beauty):  top = +2/3;  bottom = -1/3

                b.  "colors":  (not in the conventional meaning of the word color)  red, blue or green 

        2.  baryons:  made of three quarks;  proton and neutron

                a.  proton:  two up quarks and one down quark, and one of each "color"

                        ((+2/3) + (+2/3) + (-1/3)  = +1)

                b.  neutron:  two down quarks and one up quark and one of each "color"

                        ((+2/3) + (-1/3) + (-1/3)  = 0)

        3.  mesons:  made of one quark and one antiquark of complimentary "colors"

    C.  each lepton and quark has a corresponding antiparticle

        1.  an antielectron is a positron:  massless;  positive

        2.  an antidown quark:  same mass as down quark but the opposite "flavor" and "color"

II.  Nucleons:  those particles in the nucleus, the protons and neutrons

III.  Nuclide:  a unique, specific atom with a specified number of protons and neutrons in the nucleus

IV.  Isotope:  an atom of an element with a different mass due to a different number of neutrons,  carbon-14 and carbon-12

V.  Nuclear symbol:    

VI.  Nuclear Stability:  how stable the nucleus is to radioactive decay 

    A.  Nuclear Mass Defect and Binding Energy

1.        Mass defect is the difference between the mass you expect when you add the masses of all the protons, neutrons and electrons and the actual mass that is measured

a.  proton:  1.007276 amu

b.  neutron:  1.008665 amu

c.  electron:  0.0005486 amu

2.        Binding energy is the energy released when the nucleus is formed from its component parts, it is related to nuclear

        mass defect by Einstein’s equation E = mc2;  the larger the binding energy, the more stable the nuclei

    B.  Stability

        1.  plotting the number of neutrons versus the number of protons shows there is a narrow band of stability for nuclei

        2.  neutron to proton ratio

                a.  for element up to #20,  more stable isotopes have a n0 to p+ ratio of 1:1

                b.  for higher elements, more stable isotopes have a n0 to p+ ratio of 1.5:1

                c.  elements with even numbers of protons and neutrons tend to be more stable

B.       elements above #83 have no stable isotopes

C.       elements with more than 92 protons are called transuranium elements and are all radioactive

VII.    Radioactivity:  nucleus will decay or disintegrate to a lighter nucleus by giving off particles and electromagnetic radiation (energy) or both

VIII.  Types of radioactivity:  radioactive particles can be emitted from the nucleus or absorbed by the nucleus

    A.  Alpha particles

        1.  symbol:   a  or  ;  a helium nucleus (a helium atom stripped of its electrons)

        2.  has two protons and two neutrons;  mass = 4;  charge = +2 

        3.  low penetrating power (0.05 mm of body tissue), can be stopped by paper or clothing

        4.  most damaging because they are the most ionizing

        5.  usually restricted to very heavy nuclei

1.     when a nucleus emits an alpha particle its atomic mass decreases by four and its atomic number decreases by two;  when a nucleus absorbs an alpha particle its atomic mass increases by four and its atomic number increases by two

    B.  Beta particles

        1.  symbol:  b   or  ;  like an electron but it originates from the nucleus

        2.  a neutron is converted into a proton and an electron and the proton stays in the nucleus but the electron is ejected into

                the electron cloud or beyond: 

        3.  mass = 0;  charge = -1 

        4.  medium penetrating power (4 mm of body tissue), can be stopped by metal foil

          5.  medium damage

        6.  nuclei above the band of stability usually emit beta particles because they have too many neutrons  (the neutron to

        proton ratio is too high)

7.  when a nucleus emits a beta particle its atomic mass remains the same and its atomic number increases by one

    C.  Positron 

        1.  symbol:   ;  a positive electron originating from the nucleus

        2.  a proton is converted into a neutron and a positron and the proton stays in the nucleus but the electron is ejected into

                the electron cloud or beyond:

        3.  mass = 0;  charge = +1 

          4.  nuclei below the band of stability usually emit positron particles because they have too many protons  (the neutron to

        proton ratio is too low)

5.  when a nucleus emits a beta particle its atomic mass remains the same and its atomic number decreases by one

        6.  antiparticle of an electron;  when a positron collides with an electron they annihilate each other and release energy

    D.  Electron capture, also called K-capture

          1.  nuclei below the band of stability have too many protons and can lower the neutron to proton ratio by capturing an

inner orbital electron;  the captured electron combines with a proton to form a neutron:

    E.  Gamma rays

        1.  symbol:  g  or   ;  high-energy, very short-wavelength photons

        2.  mass = 0;  charge = 0 

        3.  most penetrating power, can be only partial stopped by several inches of lead or feet of concrete

        4.  least damage

        5.  when a nucleus emits a gamma ray its atomic mass remains the same and its atomic number remains the same but

                  the energy of the nucleus is lowered

    F.  Other common decay particles;  can be emitted or absorbed 

        1.  Neutron:   

        2.  Hydrogen nuclei

                a.  hydrogen: 

                b.  deuterium: 

                c.  tritium: 

IX.  Transmutation:  when a nuclide decays to a different nuclide with a different number of protons;  element is changed

X.  Decay series:  a series of successive decays involving several different nuclides of different elements; chain reactions

    A.  Parent nuclide – the heaviest nuclide of each decay series

    B.  Daughter nuclide – the nuclides produced by the decay of the parent nuclides

XI.  Nuclear equation

    A.  conservation of mass number

    B.  conservation of numbers of protons (nuclear charge)

    C.  example:  ;     the numbers on the top to the left of the arrow equal the numbers on the top to

        the right of the arrow (conservation of mass number) and the numbers on the bottom to the left of the arrow equal the

        numbers on the bottom to the right of the arrow  (conservation of nuclear charge)

XII.  Half-Life:  decay rate

    A.  the amount of time it takes for half of a sample to undergo radioactive decay

    B.  time varies from milliseconds to billions of years

                                                                                                                        Xo = initial amount,   X = final amount,

    C.    ;                                t = amount of time,    t1/2 = half-life    

XIII.  Damage

    A.  energy of the radiation (rad)

    B.  penetrating ability

    C.  ionizing ability

    D.  chemical properties of the radiation source

    E.  effects are cumulative

XIV.  Ionization:  radioactive particles cause electrons to be removed or stripped from atoms or molecules forming ions;  for       living tissues this happens at the cellular level

 

 

 

 

 

XV.  Uses of radiation

    A.  used for dating old materials

        1. carbon-14 by beta emission

        2. Uranium to lead

        3.  potassium to argon

B.       medical applications

C.       agriculture

XVI.            Radiation Detection

A.      film badge

B.       Geiger-Müller counter

C.       Scintillation counter

XVII.  Nuclear Fission and Fusion

    A.  Fission

        1.  nucleus of a large atom breaks up into more stable intermediate sized nuclei: 

        2.  energy released

        3.  chain reactions – when fission releases a neutron the released neutron can hit other large nuclei causing them to

                become unstable and break releasing more neutrons to smash into other nuclei à chain reaction

        4.  Nuclear Reactor

                a.  controlled fission chain reactions

                b.  neutrons

                c.  control rods

    B.  Fusion

        1.  two or more small nuclei join to form a larger nucleus: 

        2.  releases more energy than fission

        3.  occurs at only very high temperatures

        4.  does not produce radioactive waste

        5.  the sun