| Carbon's Valence Electrons - Carbon's uniqueness and versatility are due to its electronic configuration that is, the arrangement of electrons in its outermost energy level. Remember that we said earlier that carbon has six protons and six electrons. The first energy level contains two electrons, so how many electrons does the second energy level have? Correct, it has four. Because of this fact, carbon can either gain or lose four electrons in order to satisfy its electron requirements, and that fact makes carbon a very versatile atom. |
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| Carbon's Valence Electrons |
For example, as we saw earlier, carbon can combine with four hydrogen atoms to form methane (swamp gas), a type of compound called a hydrocarbon, because it is made up of hydrogen and carbon. (There are numerous other hydrocarbon molecules besides methane.) Or carbon can join with two oxygen atoms to form carbon dioxide (O=C=O). Carbon bonds very readily with other elements as well, such as nitrogen, sulfur, chlorine, and phosphorus. It can also combine with one or more other carbon atoms, by forming a single (CC), double (C=C), or triple (C=C) bond. You will see part of the importance of this fact when we discuss carbon chains in saturated and unsaturated bonds in the next chapter.
Now if carbon participated in an ionization process, it would have to either lose or gain four electrons. That would make the atom's electrical balance very uneven, since it would have either four more positive than negative charges, or vice versa. Therefore, carbon usually forms covalent bonds it shares four electrons. Because of this ability to share four electrons, carbon is the most versatile of all the atoms. It can combine convalently very readily with many other atoms.
Carbon also bonds with functional groups. A functional group is a group of atoms that provides a distinctive chemical property to any molecule of which the group is a part. For example, OH is what is known as a hydroxyl group, which is sometimes called an alcohol group. A hydroxyl group imparts its properties to all alcohols. When a hydrogen atom of methane (CH4) is replaced by a hydroxyl, it becomes methanol (CH3OH), or wood alcohol, which is poisonous. When ethane (C2H6 has a hydrogen atom replaced by a hydroxyl, it becomes ethyl alcohol (C2H5OH), the grain alcohol contained in vodka. We will take a closer look at functional groups in Chapter 3.
Thinking of Carbon-Based Molecules in Three Dimensions. To picture a carbon-based molecule accurately, you have to realize that the structural formula of molecules actually represents a three-dimensional object (Figure 2.10), even though, for convenience, they are usually drawn in only two dimensions. As we'll see in the next chapter not only can carbon combine with a variety of other atoms and with functional groups, but the combinations come in a variety of shapes. In some molecules, carbon atoms form a basic backbonelike arrangement for an array of atoms or functional groups that branch out to one side or another.
The shape of a carbon-based molecule is important because, as you will learn in the next chapter, some molecules (called isomers) have the same number of atoms, but because their shapes are different, they exist as different molecules. As a result, they react with other molecules in different ways, and they serve different purposes.
So the importance of the chemistry of carbon is its ability to combine in several ways with itself, other atoms, and molecules. As a matter of fact, because of their significance in living things, carbon-containing molecules are called organic (life-formrelated), as opposed to inorganic (non-carbon, nonlife molecules). Life is truly carbon-based. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 43-44)
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