STANDARD SET 6. Chemistry of Living Systems
6. Principles of chemistry underlie the functioning of biological systems.
a. Carbon, because of its ability to combine in many ways with itself and other elements, has a central role in the chemistry of living organisms
Of the naturally occurring elements, carbon is probably the most important organic element. On the Periodic Table, carbon is the first member of Group IV. Group IV members have four valence electrons, so they can become stable by either losing or gaining four electrons. Other groups will either lose or gain electrons, but with Group IV's flexibility, these atoms, particularly carbon, tend to share electrons.
Sharing electrons forms strong covalent bonds between atoms. Group IV atoms can form four covalent bonds, one for each electron. Remember that electrons have a negative charge. So these electrons repel each other. For the bonds to become stable, they must lie equal distance from each other. This arrangement forms a tetrahedron. A tetrahedron is like a camera tripod, with the legs and camera stand having equal lengths. Of the Group IV atoms, carbon forms the most stable covalent bonds.
Carbon is also unique in that it can form very stable bonds with other carbon atoms. It is this nature that forms the foundation for organic molecules. Proteins, sugars, fats and genetic material is made with a carbon backbone, upon which other elements are attached.
Because carbon has four valence electrons, one in each of the four pairs, it is more willing to share electrons with another atom (rather than grabbing them or giving them up). For example, methane is one atom of carbon bonded to four atoms of hydrogen. This would have the chemical formula, CH4. When atoms share electrons as they bond together, this is called a covalent bond. Many compounds with covalent (co- = with, together; valent = strength) bonds are not water soluble. Carbon can also form covalent bonds with other atoms of carbon, thus making long, stable chains possible. These are very important to living organisms.
The shape of a molecule of methane is a tetrahedron. The hydrogen nuclei (one proton each) are all “trying” to get as close as possible to all the electrons around the carbon, yet keep as far away as possible from each other (like + and – poles on a magnet). In a tetrahedron, there are four sides, all of which are triangles (in a pyramid, the bottom is square and there are five sides). The hydrogen protons are equally spaced in three dimensions around the carbon.
Good Chemistry Tutorials
SAS Chem - Elements
Download MDL Chime to view molecular models in .pdb format MDL® Chime
Sources for Chime PDB molecular models
Table of Molecules
Molecules from Okanagan University College: Alkanes