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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% • • • • 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)