substances - Solomon's Study Notes General Chemistry 1 Fall...

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S olomon’s Study Notes General Chemistry 1 Fall 2011 Solomon Weiskop PhD [ Substances ] General Chemistry 1
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Study Notes & Practice Problems are available to print out by registering at www.solomonlinetutor.com Solomon Weiskop PhD © Copyright 2011 All Rights Reserved
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1 1. Substances Individual atoms or molecules are “nanoscale” (i .e. submicroscopic ). This means they are too small to be seen even with an optical microscope (although they can be ‘seen’ with an electron microscope). However, if you accumulate a sufficiently large number of these nanoscale things, you eventually have a macroscale (or “macroscopic”) substance that can be held in the hand and seen with the unaided eye. That is, the word “substance” implies a macroscopic amount of atoms or molecules . In our everyday life, we experience matter as macroscale substances. Macroscale substances can be categorized in several useful ways: 1. Solid vs. Liquid vs. Gas (Physical Phases of Matter) A substance can occur in three different physical phases”: Solid, Liquid or Gas. Phase Volume Shape Solid fixed fixed Liquid fixed can change Gas can change can change For example, below ±² water is a solid (i.e. ice). Between ±²±³´µ±¶ ±² water is a liquid. Above ±² water is a gas (i.e. steam). A Phase Transition is a physical process where a substance changes from one physical phase to another: Solid ↔ Liquid: Melting/Freezing Liquid ↔ Gas: Vaporization (or Boiling) / Condensation Solid ↔ Gas: Sublimation/ Deposition
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2 Phase transitions are called physical processes (not chemical processes) because they involve no change in the underlying chemical species. For example, when liquid water freezes into ice, it continues to consist of water molecules. 2. Element vs. Compound (Chemical Species) Substances come in two varieties: Elements and Compounds. Element: A substance that consists of only one kind of atom . A piece of copper wire is elemental Copper (Cu). It consists of only Cu atoms bonded together by “metal bonding” (a different kind of bonding that we did not discuss in the previous Study Notes and which will not play a major role in our discussions). A diamond is elemental Carbon. It consists of only Carbon atoms covalently bonded together in an extended rigid network. Graphite (the “lead” in pencils) is also elemental Carbon. In graphite, the carbon atoms are also covalently bonded together in an extended network, but in a different way than for diamond with the result that the network is not so rigid but rather consists of parallel planes of carbon atoms that can glide past one another. (This is what makes it possible to write with a pencil.) The shiny grey liquid in thermometers is elemental Mercury (Hg). (Again, there is metallic bonding of the Hg atoms.) The Noble Gases (Group 8A) are also elemental. They are monatomic gases. For instance a sample of Neon gas (Ne) consists of individual Ne atoms that are not bonded together at all. In the Study Notes on
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This note was uploaded on 03/12/2012 for the course CHEMISTRY 131 taught by Professor Lacey during the Fall '11 term at SUNY Stony Brook.

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substances - Solomon's Study Notes General Chemistry 1 Fall...

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