Atomic models 2011.notebook - Ms. MironAtomic models 2011.notebook 1 September 16, 2011 Sep 1 12:00...
Transcript of Atomic models 2011.notebook - Ms. MironAtomic models 2011.notebook 1 September 16, 2011 Sep 1 12:00...
Atomic models 2011.notebook
1
September 16, 2011
Sep 112:00 AM
It all started in Greece about 2500 years ago
• Democritus • matter is discontinuous• indivisible• like grains of sand• differences in arrangement account for all elements
Sep 112:03 AM
Along came Aristotle about 100 years later...
• matter is continuous• made of earth, wind, water, fire• a magic knife could cut it forever• particles divisible
Sep 112:08 AM
John Dalton 1800's
• all matter made of atoms (indivisible)
• atoms of same element are identical
• atoms of different elements are different
• during chemical reactions atoms combine in definite proportions to form products
Sep 112:12 AM
J.J. Thompson 1906
• discovered the electron, a negative () particle that makes up part of the atom.
• They can detach themselves easily (static electricity)
• The atom is a positively (+) charged ball with electrons () imbedded
• Atoms are neutral + =
• Atoms are divisible
Sep 112:15 AM
Rutherford and the Gold Foil Experiment(McGill 1911)
• Radioactive substances can give off alpha (+), beta () and gamma (neutral) radiation
• Rutherford bombarded gold foil with alpha (+) particles
Sep 112:17 AM
Rutherford and the Gold Foil Experiment (Con’t)
Atomic models 2011.notebook
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September 16, 2011
Sep 112:18 AM
Rutherford and the Gold Foil Experiment (Con’t)
Results:• Most alpha (+) particle passed through
• A few hit the gold foil and bounced back
Conclusions:
• The atom is mostly empty
• The (+) alpha particles hit a concentrated (+) area called a nucleus
• The nucleus is Positively (+) charged
Sep 112:22 AM
Rutherford and the Gold Foil Experiment (Con’t)
Sep 112:24 AM
Rutherford’s Atomic Model
• The nucleus contains positively (+) charged particles called Protons
• There has to be an equal number of negatively () charged Electrons circling the nucleus to cancel each other out
Sep 112:25 AM
The Problem with Rutherford’s Model
• Opposite charges attract each other; the atom should collapse.
• What prevents the () electrons from crashing into the (+) protons ?
Sep 112:27 AM
The RutherfordBohr Model
Bohr’s Contribution • White light is broken into the electromagnetic spectrum
Sep 112:28 AM
• Bohr concluded electrons could occupy specific orbits (energy levels, shells)
• Electrons could jump orbits when energy (heat or electricity) is supplied
• When an electron falls back to it’s original orbit it gives off the energy in the form of colored light
Atomic models 2011.notebook
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September 16, 2011
Sep 112:30 AM
RutherfordBohr Model
• Drawing the first 20 elements
• Look at the atomic #
• Atomic # = the # of protons (in nucleus)
• # of protons = the # of electrons (in orbit)
• Carbon: 6 protons = 6 electrons
• Electrons fill specific orbits or Energy Levels
Sep 112:33 AM
Orbits or Energy Levels
• 1st level: 2 e
• 2nd level: 8 e• 3rd level: 8 e • 4th level: 2 e
Sep 118:58 PM
BohrRutherford Diagrams
1. Protons go in nucleus2. Fill each shell before moving to the next
Ex: Nitrogen (N) Atomic # 7 7 protons, 7 electrons
Sep 119:08 PM
Ex: CalciumAtomic number 2020 protons, 20 electrons
Sep 112:39 AM
The Simplified Model(Similar to RutherfordBohr except...)
• Chadwick discovered the Neutron• It is in the nucleus• It holds protons together• It is neutral• The number of Neutrons is determined by,
Atomic Mass Atomic # = # neutrons• The Atomic Mass can also be determined by # Protons + # neutrons = Atomic Mass
Sep 119:10 PM
Ex: Magnesium (Mg)Atomic number 12Atomic mass 2412 protons, 12 electronsmass protons = neutrons24 12 protons = 12 neutrons
Atomic models 2011.notebook
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September 16, 2011
Sep 119:17 PM
Ex: Aluminum (Al)Atomic number 13Atomic mass 2713 protons, 13 electronsmass protons = neutrons27 13 = 14 neutrons
Sep 119:21 PM
Match the protons, electrons and neutrons with the elements in the table
Element Protons Electrons Neutrons
Chlorine (Cl)
Potassium (K)
Carbon (C)
8
6
12
184019 6
194018
12 21
3517 18
17
6
9
14
Sep 112:39 AM