Chapter 2.1-2.4 & definition of moles Atoms, Molecules, and Ions.
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Transcript of Chapter 2.1-2.4 & definition of moles Atoms, Molecules, and Ions.
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Chapter 2.1-2.4 & definition of molesAtoms, Molecules, and Ions
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Atomic Theory (Dalton)
1. Elements are made up of atoms (Na, K, H, etc.)
2. Atoms of same elements have same properties
3. Atoms are neither created nor destroyed in a chemical reaction (Law of Conservation of mass)
4. Compounds are formed by combinations of elements in fixed ratios.
H2O 2 H, 1 O
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• What makes an atom?– How can one get that information?
• What makes an egg?– How can you get that information?
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ATOM
Electron (e) Proton (p) Neutron (n)
Charge -1 +1 0(au)
Mass 1/1837 1 1(au)
1 amu = 1.66 x 10-24 g
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Discovery & Characterization of the
electron (e)
• Cathode Ray (-) charges electrons
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Thompson’s Experiment
• With electrically charged plates and a magnet
• Charge/mass ratio for an electron– (e/m) = 1.76 x 108 Coulomb/g (or
C/g)
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Millikan oil-drop experiment
Charge of e- = 1.60 x 10-19 Coulomb (C)Mass of e- = 9.10 x 10-28 g
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Radioactivity• Spontaneous emission of
radiation
α ( )
β ( ) electron
γ ( γ)
• Note: 238 is # protons + # neutrons, 92 is # protons
• α is attracted to (-) plate and hence must contain (+) charge
23892U
42He
01e
00
23892U
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Rutherford’s Experiment
• Atom– Protons (p), Neutrons (n), and
Electrons (e-)•How are they together?•Are they uniformly spread over?
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Rutherford’s Experiment
•α-Particles are allowed to strike a gold plate
»Most particles go through»A few go backward
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Rutherford’s Experiment
• Can we predict what is going on in Rutherford’s Experiment?
• Why do α –particles (used as balls) go through undeflected?
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Rutherford’s Experiment
• Conclusion– An atom is mostly made up of
empty space (like an open door) with a massive nucleus (like a concrete wall), occupying a very small volume.
– Nucleus has protons and neutrons, electrons revolve outside.
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Isotopes, Atomic Number, and Mass Number
• Atomic number = Number of Protons
• Mass number = # Protons + #
Neutrons
• Can you define “isotopes”?– Same elements?– How are they different?
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Isotopes, Atomic Numbers, and Mass Numbers
•Here is an example of Isotopes. •Remember that the top number is the mass # and the bottom number is the atomic #.
11H
21H 3
1H
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Average Atomic Mass• Avg. mass = P1M1 + P2M2 + …
– P1 = % abundance for Isotope 1
– M1 = Mass for Isotope 1
– P2 = % abundance for Isotope 2
– M2 = Mass for Isotope 2
Refer to Problem 29 (Pg. 72)
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Mass Spectrometer• Obtain atomic and molecular
weights • Need gaseous samples• Ionization of sample by high
energy electrons• Pass gaseous ions through
poles of a magnet• For ions carrying the same
charge, more massive particles will be less deflected than the less massive particles. Thus, mass separation takes place.
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Mole & Number• 1 thousand = 103 = 1000• 1 million = 106
• 1 mole = 6.022 x 1023 (Avogadro’s number)
• 1 mole H atoms = 6.022 x 1023 H atoms
• 1 mole H2O molecules = 6.022 x 1023 H2O molecules
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Mole & Gram (Molar Mass)
(Remember: M-g-P = mole-gram-Periodic Table)
• 1 mole C weighs 12.0107 g ≈ 12.0 g C atoms – Found on the Periodic Table
• 1 mole H weighs 1.00794 g ≈ 1.00 g H atoms
• 1 mole H2O = 2(1.00794) + 15.9994 ≈ 2 + 16 = 18 g H2O molecules
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