Announcements - 9/10/02
•Labs have begun!
•Quiz #1
• available until 12:30 Thursday
•Exam #1
•Info page now online!
•Conflicts?
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Plum Pudding and Rutherford
“The atom has a structure like plumpudding” - J.J. “Boom-Boom” Thomson
1910: Ernest
Rutherford
-shot α-particles at
a thin foil of gold
-led to the Nuclear
model of the atom
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The Nuclear Atom
„Atoms are composed of:
electrons (e-): neg charge, light
protons (p+): pos charge, heavy
neutrons (n0): NO charge, heavy
#p+ = #en0 (mass) ≈ p+ (mass) ≈ 2000 x e- (mass)
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Atomic Size
They sure are small!
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How do Elements Differ?
„Elements classified by #p+:
Atomic Number (Z) = #p+
„What about #n0?
#n0 affects mass number (A)
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Elemental Symbols
Standard notation for a Nuclide:
Mass
Number
(#p+ + #n0)
Atomic
Number
A
X
Z
Element
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Isotopes of Hydrogen
1H:
1 proton, 0 neutrons, 1 electron
1 proton, 1 neutron, 1 electron
- Deuterium
2H:
1 proton, 2 neutrons, 1 electron
-Tritium
3H:
-They all behave the same, chemically
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More Isotopes
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Quantifying Matter: Moles
„ An SI Unit (No):
1 mol = 6.022137 x 1023 species
Avogadro’s Number
-mole: Latin (“heap, pile”)
Amedeo Avogadro’s Hypothesis (1811):
Equal volumes of different gases contain equal
numbers of particles
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Quantifying Atomic Mass
¾ New Unit: amu (atomic mass unit)
By definition:
mass of 12C nucleus = 12.000 amu
¾ For a mole of an element, we use the molar
mass (= g/mol) which is numerically
identical to the #amu for the element:
1 mol
12C
= 12.000 grams (exactly)
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Organizing the Elements
„ Late 1800’s: Mendeleyev arranges elements in
order of increasing atomic mass
-finds periodic trends in reactivity:
- arranges so that elements with similar reactivity are grouped
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The Periodic Table
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Groups on the Periodic Table
• Group 8A (far right): Noble Gases
-VERY unreactive
• Group 1A (far left): Alkali Metals
-Soft, low m.p. metals
-VERY reactive (they react with water to give off H2)
• Group 2A: Alkaline Earth Metals
• Group 7A: Halogens
-NON-metals (insulators, brittle, gaseous)
• Group 6A: Chalcogens
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Molecules
• Definition: Two or more atoms bound
together
• Identified by a Formula:
Molecular Formula – gives the actual
numbers and types of atoms in molecule
Empirical Formula – gives the relative
numbers of atoms in molecule (smallest wholenumber ratio)
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Visualizing Molecules
CH4
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Not all Compounds are
Molecules
Let’s look at the reaction of an Alkali
Metal (Na) and a Halogen (Cl):
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Ionic Compounds
Formed by reaction of a metal with a non-metal:
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