44 | The History and Use of Our Earth’s Chemical Elements type 2 diabetes. The healthiest oils and fats are polyunsaturated or monounsaturated fats,

44 | The History and Use of Our Earth’s Chemical Elements type 2 diabetes. The healthiest oils and fats are polyunsaturated or monounsaturated fats,

which include olive oil, canola oil, soybean oil, and corn oil. These have not been saturated with hydrogen to produce solid fats.

Halogenation: Another common substitution reaction in which hydrogen atoms are replaced by halogen atoms. (See the group VIIA of the periodic table for more on this group of active halogen elements.) This is an example of a substitution-type reaction that forms a group of compounds known as chlorofluorocarbons or CFCs. CFCs are chemicals formerly used as refrigerants in air conditioners and to create pressure in aerosol cans that some sci- entists claim are partially responsible for the hole in the ozone layer of the atmosphere. The two most destructive halogenation compounds to the ozone layer are trichlorofluoromethane (known as Freon-11) and dichlorodifluoromethane (known as Freon-12). New refrigerants have been developed since the chlorofluorocarbons harmful to the ozone have been banned by most countries.

Polymers: Formed when multiple addition reactions occur that link many smaller hydro- carbon molecules into long chains. Ethylene (C 2 H 4 ) and propylene (C 3 H 6 ) are alkynes with the ability to string their molecules together in what is known as “addition polymerization” to form long chains of repeating molecules. The repeating units in the chain are known as

monomers ; for example, each of the individual C 2 H 4 monomer is formed into a straight polymer chain. Either ethylene or propylene (as well as other hydrocarbons) is utilized in the production of valuable synthetic products such as polypropylenes, polyvinyl chloride (PVC), and Teflon. Many other products, such as plastics, are manufactured from the millions of tons of polymer types of hydrocarbon molecules produced in the United States each year. A process of polymerization is also used to produce very high-octane gasoline.

Aromatic hydrocarbons: Unsaturated cyclic (ring) molecular compounds that resist addition reactions. These ring-shaped hydrocarbons are highly unsaturated. They are called “aromatic” because of their distinctive aroma that aided in their discovery, as well as the unique arrange- ments of one or more of their carbon rings. The hexagonal-shaped benzene ring is the most commonly shaped aromatic molecule. All other aromatic hydrocarbons are derived from one

or more benzene (C 6 H 6 ) groups. They are very reactive and versatile compounds made from petroleum or coal tars from which many useful products are manufactured. Hydrocracking of petroleum and coal: Hydrogen is used for a process called destructive hydrogenation, which breaks down large hydrocarbon molecules to form more useful liquid and gaseous fuels. Gasoline is a mixture of branched-chain alkyne paraffins, cycloparafins, and some aromatics with an octane number of at least 60 (or higher) that can be ignited by a spark plug inside an internal combustion engine. There are several processes used to produce different qualities of gasoline, but by far, most is produced by the catalytic decomposition of crude oil and unrefined petroleum products at high temperatures. The catalytic cracking process produces gasoline with an octane rating of 80 to 100.

Reducing agent: Hydrogen is electropositive when it provides electrons to other substances in chemical reactions and, thus, is a reducing agent. Reduction is the opposite of oxidation.

Lighter-than-air balloons: Hydrogen gas that is lighter than air was used to inflate some of the early “free flight” balloons and was used later in some dirigibles until the danger of explo- sions led to the use of helium as a substitute.

As a rocket fuel: Large amounts of liquid hydrogen, along with liquid oxygen, are used in the U.S. Space Program.

Guide to the Elements | 45 As an “ion” fuel for nuclear rocket engines: By stripping the single electron from a hydrogen

atom, you end up with a light positive particle (proton) that can be accelerated by a negatively charged source. A great mass of protons reach a very high velocity in an ion engine as they are ejected, thus producing thrust for the engine.

As a possible fuel for “fuel cells”: Hydrogen and oxygen gases can be combined in a fuel cell to produce electricity with water as the only by-products. This reaction is the opposite of the electrolysis of water, in which electricity separates the water molecules to form H 2 and O 2. On May 14, 1996, the Daimler-Benz German automobile maker, in cooperation with Ballard Power Systems of Canada, announced development of the first fuel cell–powered passenger car. A similar fuel-cell power system developed by the Canadian company was tested on several buses in cities in the United States. The source of the fuels, at least for the near future, will be natural gas for the hydrogen and air for the oxygen. The fuel-cell power system produces very little pollution and has proven to be a reliable source of both electricity and drinking water for astronauts. However, both the U.S. government and energy companies have reduced their research support for fuel cells designed as a long-term replacement of petroleum for transpor- tation. It is expected that research to improve the practicality of fuel cells for transportation use will increase as the cost of petroleum increases.

Examples฀of฀Compounds Acids฀and฀Gases

Anhydrous ammonia (NH 3 ) is a colorless gas with a sharp, irritating odor, lighter than air, easily liquefied. An important commercial compound. It was the first complex molecule identified in outer space.

Boric acid (H 3 BO 3 ) is a solid, soft, smooth, solid weak acid that is used in pharmaceutical and cosmetic industries. Carbonic acid (H 2 CO 3 ) is produced by dissolving carbon dioxide in water. When formed under pressure, it is the gas used in carbonated drinks. In nature, it dissolves the limestone in caves, resulting in the formation of stalactites and stalagmites. It is corrosive as are other acids, although it is considered a rather weak acid.

Hydrochloric acid (HCL) is also known as hydrogen chloride, and in a less than pure form it is commonly called muriatic acid. It is used by many industries and is mainly obtained as a by-product of the organic chloride chemicals used in the manufacturing of plastics. It can be produced in pure form by exploding a mixture of hydrogen and chlorine gases. The stomach’s digestive juice is a form of hydrochloric acid.

Hydrogen peroxide (H 2 O 2 ) in a purified form is explosive. In a dilute form in water, it is used as an antiseptic and oxidizing agent. Hydrosulfuric acid or hydrogen sulfide (H 2 S) is known for its “rotten egg” odor and is a deadly poisonous gas even at 100 ppm of air. The laboratory reaction is FeS + 2HCl → H 2 S↑ + FeCl 2 . Nitric acid (HNO 3 ) is an important industrial acid used to alter or produce many products such as fertilizers and explosives. It reacts with ammonia to produce ammonium nitrate, an important commercial chemical.

Sulfuric acid (H 2 SO 4 ) is the most used acid in many industries and chemical laboratories. Produced in large batches, it is stable and safe for storage and shipment in vast quantities in