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In nature, the atoms of various elements combine to form compounds. They (the atoms) generally arrange themselves into structures called molecules. The atoms use their electrons as a microscopic connecting rod (called a chemical bond) which acts as a framework for the molecule. If you have ever built an animal from gum drops using toothpicks, you already have the idea. The gun drops are the atoms (different flavors are sort of like different elements). The toothpicks are the bonds that hold the atoms in place. The entire structure is the molecule. There are three kinds of chemical bonds ionic-these bonds form between ions, and usually bond a metallic element to a nonmetallic one; covalent--these bonds form between atoms which have not become ions and usually occur between nonmetals metallic---these form between atoms of metals We will have a great deal more to say about bonding later on, but for now, this knowledge should get you through most of the introductory work we will be doing. No one has actually seen a molecule in the same sense that you can look out the window and see the Peace Bridge. People have detected them, and understand a great deal about their size, their shape and other properties. But they have not seen them. Nonetheless they...I...all of us scientists constantly draw pictures of molecules...not precise representations, but diagrams that show how the atoms are hooked together. It's sort of like the blueprint for a building. It isn't really an exact picture of the building. But it tells you a lot about it: where the rooms are, how big they are, the locations of all the windows and doors, and so forth. Here is a diagram that represents the molecule methane: This is called the structural formula of methane. What this diagram says is that there are four atoms of hydrogen and one atom of carbon in each molecule of methane. Each hydrogen atom is connected to a central carbon atom by a chemical bond...that is what those lines represent. Here is another representation of methane: This is called the chemical formula for methane. It does not tell us as much about methane as the first diagram. This tells us that, in a molecule of methane, we will find 4 hydrogens for each carbon. Not nearly as much information but, then again, it does not take up as much space. Here are a couple of other molecules: Chemical Name Chemical Formula Structural Formula Notice how you can sometimes have two bonds between atoms. This is called a double bond, and appears in ethylene. The acetylene molecule contains a triple bond.

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