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moleculescompounds - Solomon's Study Notes General...

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S olomon’s Study Notes General Chemistry 1 Fall 2011 Solomon Weiskop PhD [ Molecules & Compounds ] 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. Molecules and the Covalent Bond It often happens that atoms “bond” together in certain fixed numbers to form Molecules. For example a water molecule has in it three atoms (one oxygen atom and two hydrogen atoms) bonded together. The atoms within a molecule are held to each other by what are called “C ovalent Bonds”. We will discuss c ovalent bonds in glorious detail later in this course. For now, however, it will suffice to mention a few basic facts about them. First of all, a covalent bond results when two atoms share a pair (or several pairs) of electrons. Usually (but not always*) each of the atoms participating in the bond each supply one electron of the pair comprising the bond. In the figure below, an X atom and a Y atom form a covalent bond thereby making an XY molecule: Here X and Y stand for any two generic atoms. The dots represent electrons. (This is a very common notation which we will use a lot.) Atoms typically have several electrons but in this figure I’m not showing all of them, I’m only showing one electron per atom (the one the atom will use in making the bond). The line represents the covalent bond between X and Y. I’ve shown two dots at the ends of the bond to emphasize the fact that a covalent bond consists of two electrons being shared between atoms. Usually these dots on the bond itself are not shown . Important Point : Atoms are electrically neutral. So when they get together to form a molecule, the molecule also is electrically neutral. * Sometimes one atom supplies both of the two electrons in the bond. This is called a coordinate covalent bond ”. We’ll discuss them more next semester.
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2 A single line indicates a single bond, meaning 1 pair of electrons is shared between atoms X and Y A double line indicates a double bond, meaning 2 pairs of electrons are shared between atoms X and Y A triple line indicates a triple bond, meaning 3 pairs of electrons are shared between atoms X and Y Triple bonds are as high as it goes. There aren’t any quadruple bonds. The atoms in a molecule are bonded together in a certain specific arrangement and shape. For instance, a molecule of water can be represented something like this Notice that the water molecule has a specific arrangement of its atoms: Each of the two H atoms is singly-bonded to the central O atom (rather than to one another). Water molecules also have a characteristic bent shape (indicated in the figure). H 2 O is called the Chemical Formula for water. We’ll be using chemical formulas a lot.
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