11 The Atomic Nature of Matter
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Transcript of 11 The Atomic Nature of Matter
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11 The Atomic Nature of Matter
• atoms• Molecules• Chemicals & matter
• Homework:• RQ: 6, 8, 11, 13, 14, 18, 22, 23, 24.• Ex: 2, 3, 8, 9, 17, 19, 27.
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The Atomic HypothesisConsider the following process:
Smash a rock
Smash the pieces
Continue till rough powder
Grind the powder indefinitely
When does the process stop?
Is it still rock when you are done?
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Atomic History
• Hypothesized in 5th Century B.C. (Greece)• Aristotle 4th Century B.C. did not believe in
atoms. Taught 4-element idea (earth, air, water, fire)
• Dalton 1800s England revived atomic idea• Brown 1827 hypothesized atoms caused
oscillation of microscopic particles• Today we know 88 naturally occurring
atoms and about 30 more lab created
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Unicellular Algae
Light Microscope
(SEM) Electron Microscope
SEM, about 100 times better resolution
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Resolution is Related to Wavelength of the Waves
Objects larger than distance between waves leaves a clear “shadow”.
Objects smaller than distance between waves do not.
Shorter waves give us more “resolution”
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Atoms
• years of experimentation led to a rough model: our own solar system, which is mostly empty space.
• “middle” of the atom is nucleus• “outside” of atom is an electron shell
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The Nucleus and the Atom
• nucleus: “protons” and “neutrons”• each of similar size and mass• proton has positive charge• neutron has no charge• electrons have negative charge and
are much less massive
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element• substance in which each atom has the
same number of protons (neutrons may vary)
• atomic number = # protons in atom• mass number = # protons + # neutrons• isotopes have same # protons but with
varying # neutrons. Example: • Hydrogen: 1 proton, 0 neutron, 1 electron• isotope: 1 proton, 1 neutron, 1 electron
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chemical properties
• depends on number of electrons which must equal number of protons for uncharged atom.
• atoms with more (or less) electrons than protons are called “ions” and have different chemical behavior.
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Periodic Table
• elements in same column have similar chemical properties due to similar electronic structure.
• major groups: metals, metalloid, non-metal• symbols are used to label the different
atoms. • some symbols come from different
languages e.g. gold = Au, silver = Ag, etc.
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The Periodic Table of The Elements (the distinct atoms)
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Molecules
Molecules are groups of atoms. Here are a few examples.
oxygen ammonia methane water
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Terminology• Element – atoms with the same number of protons.
• Molecule – smallest particle of chemical substance that has the same composition and chemical properties, e.g. water molecule.
• Compound – chemical substance formed from 2 or more elements and which has a definite chemical formula. Note that crystals such as NaCl are not molecular.
• Mixture – substance with components that have not combined chemically.
• Chemical Substance - an element, compound, or mixture.
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A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions.
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Summary• atoms make up matter, atoms are: protons,
neutrons, electrons, type of atom determined by # protons.
• molecules are formed from atoms• atomic and molecular structures determined by
electron microscopy• definitions: element, mixture, isotope,
compound, substance.• periodic table: columns have similar chemical
properties.