Last updated 8-4-09

3: Building Compounds from the Elements

In the last tutorial, you got an introduction of how atoms bond with each other. In the example on the left, we see that carbon has four vacancies for electrons. Fluorine has one vacancy. The shared electrons are in the middle of a tug-a-war. Protons from both the fluorine and the carbon atoms pull on the electrons. This brings the atoms together. The white arrows show the movement of the electrons. The yellow arrows show the pulling force of the protons. So the four fluorine atoms bond to the single carbon. The formula is CF4.

To the left is methane, which is natural gas. One carbon and four hydrogen atoms make up methane. This is another example of electrons being shared by atoms. Shown are just 3 electrons, not all 10 that are there. But you can still see how they move around and are shared by different atoms. This kind of bonding is called covalent bonding. "Valence" comes from a Latin word meaning "capacity and power." The valence electrons give the atoms the capacity and power to combine (bond) with other atoms. Here the valence of carbon is 4, and hydrogen is 1. That's how many electrons are involved in bonding.

To the left are atoms of magnesium and oxygen. They are bonded by ionic bonding. An ion is an atom with a charge. Both of these have a charge. Magnesium has 12 protons (+) and normally 12 electrons (-), but here, the oxygen has taken the outer two electrons leaving magnesium with only 10 electrons (-). That makes magnesium's net charge of positive 2 (+2). Oxygen, however, has gained two extra electrons, so it has 8 protons and 10 electrons, giving it a net minus 2 (-2) charge. These atoms now have opposite charges, so they attract each other. That is called ionic bonding.

Compounds are often classified as Organic and Inorganic.
In the below image, the rocks, water, and soil contain inorganic compounds, and the tiger, grass, and trees contain organic compounds. You can think of organic compouds as those more likely found in organisms. Inorganic compounds, in contrast, are those created by forces within the Earth. Minerals, for example would be inorganic compounds.

When we look at what things are made of, we find that elements usually make a small compound that is then used as a building block for larger compounds. These larger compounds are then used as building blocks for even larger compounds. It's an efficient approach. An analogy would be to draw a brick with 2 long lines, 2 short lines, and a red rectangle (these are the elements). These elements, bonded together, represent a small compound (1 brick) that is used to build a larger compound (layer of bricks). The layer of bricks becomes the building block for a wall of bricks.

Wall of bricks integrated into final "organism" or structure.
The wall of bricks becomes an integral part of the final organism. So remember, even though we are confronted with something complex, like this van's paint job, we look for the simpler, smaller, and repeating building blocks that made it-- 2 long lines, 2 short lines and a red rectangle.
The building blocks for inorganic compounds are quite different than those of organic compounds. Let's first focus on the inorganic compounds in the next tutorial.
<-CHM151  Inorganic Compounds->

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