¶ … Chemistry at work. Every facet of our existence -- living or non-Living -- is a completed or ongoing chemical process.
More than one hundred elements (basic units of chemical compounds) have been identified thus far: most are stable, others are reactive and dangerous. The ones with the highest atomic numbers (total number of protons or electrons in the atoms) are created in laboratories and have brief existences. About twenty are radioactive -- and the harm their intrinsic energies can wreak was in evidence in Hiroshima and Nagasaki towards the end of Word War II (Hachiya, 1945).
Yet, most elements are the bases of food, shelter and clothing -- the basic necessities of life. The air we breathe is a cocktail composed of approximately 78% nitrogen gas, 20% oxygen gas, carbon dioxide and other gases in trace amounts (Aquatext, 2000). Upsetting this critical balance causes adverse effects such as global warming and holes in the ozone envelop. All life forms are one big composite of chemical compounds and processes.
All atoms in elements are categorized in the Periodic Table based on how electrons fill up various levels or shells (WebElements, 2003). These shells are orbits in which electrons move around the nuclei. Each nucleus is composed of protons and neutrons. So why are these elements not self sufficient? Why do these elements get together to form compounds? The reason is simply because there is an inherent stability in a complete orbit or shell that every element seeks to achieve.
An element that is deficient in electrons will find is easy to acquire electrons from another atom to achieve a completed shell. Alternatively, if it is energetically favorable to give up electrons to achieve stability of a completed lower shell, the element does exactly that. A third choice is to share electrons with another element such that both elements can claim completed shells.
The above paragraph illustrates the difference between inorganic and inorganic chemistry. Consider this example: Sodium (Symbol Na) has eleven electrons. Its inner level needs two electrons, the next level needs eight, and the third level needs seven -- but has one electron. Chlorine (Symbol Cl) has seventeen electrons: two in the innermost level, eight in the second and seven in the third -- one short of a complete third level. Sodium and Chlorine can boast completed shells if chlorine acquires an electron from sodium. This yielding of an electron by Sodium results in the creation of two ions: Na+ and Cl-. The two ions are linked by an ionic or electrostatic interaction. In the periodic table, the elements on the left more readily give up electrons and those on the right acquire electrons. These form inorganic compounds. In addition, elements like metals form compounds from inorganic bonds (Lee, 1999).
What happens to the elements in the middle of the Periodic Table? These are elements that have electrons that do not render them partial to giving up or accepting electrons. Carbon (Symbol = C) has four electrons in its outermost shell. To complete its shell (8 electrons) carbon can share electrons each of its electrons with a Hydrogen, other Carbons or Nitrogen and Oxygen such that both elements use the shared electrons. The bonds by electron-sharing are covalent bonds. The covalent bond is the basis of an organic compound, and consequently, organic chemistry (Lee, 1999).
The arrangement of the four electrons around the carbon lend it a tetrahedral (equal on four sides in three dimensions) geometry. The simplest organic compound is methane (inflammable gas found in sewers and coal mines) where a single carbon atom is covalently linked to four hydrogen atoms. In this way, each hydrogen atom can claim two electrons needed to complete its shell (its own and one from carbon). The four carbon electrons and one each from the four hydrogen atoms complete its shell of eight. If one considers a chain of carbon atoms linked together carbon to carbon (C-C) with associated carbon to hydrogen (C-H) bonds, an organic molecule is formed. These compounds are straight chains, rings, or chains with cross- links and branches.
The simplest of organic molecules are alkanes. Alkanes are formed by single covalent bonds of carbons linked together, aCH3-bCH2-CH2-CH2-... The (-) denotes a single bond. Each carbon atom is attached to four other bonds (Morrison & Boyd, 1983, p. 45). It denotes the completion of a shell for each carbon. The first carbon atom (a) in the above chain is attached to three hydrogen atoms and the next carbon atom (b). Alkenes are formed when carbon atoms are...
aCH2=bCH-CH2-CH2-... (Morrison & Boyd, 1983, p. 267) In cases where two carbon atoms share six electrons they form a triple bond, e.g., aCH bC-CH2-CH2-... These are alkynes (Morrison & Boyd, 1983, p. 555).
Alkanes are saturated compounds. Alkenes and alkynes are unsaturated. Saturation is when every unpaired electron is paired with an electron from another atom to form a covalent bond. Since all the electrons are paired and the valence requirements are met, the compound is said to be saturated. In the case of compounds with double and triple bonds, the absence of extra hydrogen atoms for saturation cause atoms to use these unpaired electrons to form double and triple bonds. Unsaturation results because the need to have each electron covalently paired in a single bond is not met. Generally, removal of hydrogen from a compound causes unsaturation. Conversely, introduction of hydrogen results in saturation.
When Dupont Inc. created the world's first polymer-Nylon, it took the world by storm. These fibers, plastics and other composites, indispensable to life today, are the result of a process called polymerization. Simply defined, polymerization is the joining of many small molecules to form larger molecules of many tens of thousands of molecules (Morrison & Boyd, 1983, p. 436). Consider the simplest alkene-ethylene (CH2=CH2). Under pressure, heat and oxygen, ethylene gives rise to a larger molecule that looks like ~~CH2-CH2-CH2-CH2-CH2-CH2-CH2~~ or ( -- CH2CH2 -- )n (n could be several thousands or hundreds of thousands). The resulting compound is called polythene and is the main component of most grocery and garbage bags. Introduction of chlorine molecules into the above mix results in polyvinyl chloride ( -- CH2CHCl -- )n from which cars' windshields are made. While the above are man-made, polymers have been in existence in nature since the beginning of life -- without which life would not exist. Proteins and DNA are essentially polymers.
Consider an alkane, an alkene or an alkyne. In addition, also consider the six Carbon atom ringed structure benzene. While these are basic molecules, other compounds can be derived from these by replacing one or more hydrogen atoms with other compounds or ions called functional groups. These functional groups lend specific functions when they are attached to basic organic molecules. Let's represent alkanes, alkenes, alkynes (minus one hydrogen atom that will be replaced by a covalently bonded functional group) with the letter R (for alkyl, alkenel or alkenyl) and the benzene ring (minus the hydrogen) with Ar (Aryl - C6H5); use the generic alphabet "F" for a functional group. The compound then is R-F or Ar-F.
If F = OH, the resulting compound R-OH is an alcohol. Methyl alcohol (or methanol) Chapter 3-OH is fatal if consumed; ethyl alcohol CH3CH2-OH however, forms the basis of all consumable alcohols (Morrison & Boyd, 1983, p. 455).
On replacing the R. with the Aryl group Ar, a phenol C6H5-OH results (Morrison & Boyd, 1983, p. 957).
Ether is formed by an oxygen atom covalently bonded to two separate R. groups (R-O-R') or two Ar (Ar-O-Ar) groups or even an R. And an Ar group (Ar-O-R). Diethyl ether (CH3CH2-O- CH2CH3) or ethyl methyl ether (CH3CH2-O-CH3) are examples (Morrison & Boyd, 1983, p. 533).
Halides are the ions of halogens. We have already discussed how a chloride ion is formed from chlorine. The chemistry is the same for the rest of the halogens. Fluorine (F), Bromine (Br) and Iodine (I) are the other halides. Halides are represented by the symbol X. Thus, R-X or Ar-X are called halides. Chapter 3-Cl - methyl chloride and C6H5-I iodo-benzene are examples (Morrison & Boyd, 1983, p. 202).
The functional group for aldehydes and ketones is the carbonyl group (>C=O). The carbon atom is attached by a double bond to oxygen. Whether the compound is an aldehye or a ketone depends on what two groups complete the carbon valence. If one of those groups is hydrogen, then the compound is an aldehyde. The other group in an aldehyde can be either an R. Or an Ar group. The simplest aldehyde is acetaldehyde, CH3HC=O. Benzaldehyde C6H5HC=O is another common aldehyde. A ketone, on the other hand, results when the carbonyl group is attached to two R. groups, two Ar groups or an R. And an Ar group. Dimethyl ketone CH3CH3C=O is an example; as is acetophenone CH3C6H5C=O. For aldehydes and ketones the "bold" group or H. indicates that they are attached to the C. Of CO and not to the first R. Or Ar (Morrison…
