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Law of Physics
chapter 18
A moving charge looses energy =
electron would eventually be pulled
into the nucleus = Rutherford atom
would be unstable
New ideas as to the parts of and
arrangement of an atom
• Proton + Rutherford 1917
• Neutron neutral Chadwick 1932
• Electron – Thomson 1897
Carbon 12
• Nuclear symbolism
mass number protons + neutrons
12
C
atomic number = # of protons
6 electrons 6 protons +
6 neutrons
6
Carbon 14
• Isotope = same element with different mass
(more neutrons)
mass number protons + neutrons
14
C
atomic number = # of protons
6 electrons –
6 protons +
8 neutrons
6
• Atomic number determines which element
• Mass number determines the isotope-same
atomic number, different mass because of
amount of neutrons.
• There is usually more than one type of isotope
for all atoms
Atomic mass unit
• Chadwick -1932 neutron amu = 1.008666 = 1
• Rutherford -1919 proton amu = 1.007276 = 1
• Thomson -1897 electron amu = .0005486 = 0
Carbon 12
• 1 atomic mass unit = 1/12 the mass of a
carbon atom
• Mass of Carbon = 12.00000amu
• 6 protons = 6 x 1.007 = 6.042
• 6 neutrons = 6 x 1.009 = 6.054
• 6 electrons = 6 x .0005 = .003
• 6.042 + 6.054 + .003 = 12.099
• .009 is the mass that is lost. It goes to energy
and is called the nuclear binding energy. With
this absence, the nucleolus will not fly apart.
• E = MC2
• The natural tendency of the nucleolus is to repel
the + charges and fly apart. The deficient of the
amu .009 holds it together.
• Overcomes repulsion from neutrons and protons
• P-P, P-N, N-N
• Strong nuclear force
Atomic mass/weight
• Atomic mass = mass of a given isotope of an
element Carbon 12 or Carbon 14
• Atomic weight = weighted average of the
atomic masses of all the naturally occurring
isotopes of an element
Atomic weight
• % abundance of naturally occurring isotopes by Atomic
mass
• 12.00 = 99.0%
• 13.02 = 0.10%
• 14.04 = 0.90%
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•
12.00 x .9900 = 11.88amu
13.02 x .0010 = .0130amu
14.04 x .0090 = .13amu
11.88 + .0130 + .13 = 12.023amu = 12.02amu = atomic
weight of Carbon. The others are isotopes (Carbon 14)