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Two basic groups of chemical compounds are formed from elements: salts and non-salts. Within each group are families of compounds that present particular hazards. By understanding these family relationships, emergency responders can determine the general hazards of materials by identifying the family to which each belongs. This "rule of thumb" information, however, does not eliminate the need to research the chemicals further before mitigation actions are taken. The first basic group of compounds, the salts, were covered in the September 1997 column.
Photo by Robert Burke
Propane is an alkane hydrocarbon that is a flammable gas.
The second basic group of chemical compounds will be referred to here as non-salts, or non-metal compounds. Non-metal compounds are combinations of non-metallic elements. These are the elements to the right and above the dividing line between metals and non-metals on the Periodic Table of the Elements.
Non-metals and their compounds may be solids, liquids and gases. Some may burn; some may be toxic; and they may also be reactive, corrosive and oxidizers. The largest quantities of hazardous materials encountered are made up of non-metal (non-salt) materials. Non-metals combine in a covalent bonding process. When elements bond covalently, the bonding electrons are shared between the elements.
Non-metal compounds are formed from non-metal elements. For example, when the non-metal carbon is combined with the non-metal sulfur, the compound formed is carbon disulfide. It is a poison by skin absorption and is a highly flammable, dangerous fire and explosion risk, has a wide flammable range from 1% to 50%, and can be ignited by friction. Carbon disulfide also has a low ignition temperature and can be ignited by a steam pipe or light bulb. Non-metal compounds can be represented in three ways: chemical name, molecular formula and structural formula. In the above example, carbon disulfide is the chemical name, the molecular formula is CS2 and diagrammed below is the structural formula:
The structural formula illustrates the way bonding takes place between the atoms of elements in a compound. The molecular formula shows the numbers of each of an element atom in a compound. Responders may encounter the molecular formula along with the name; however, it is unlikely they will see a structural formula in the field.
As can be seen with the structural formula of carbon disulfide, there are two bonds between the sulfur and the carbon. This configuration of bonding is referred to as double bonding. Double bonds are very unstable, which is why carbon disulfide is so very flammable.
Carbon dioxide is another common non-metal compound. Carbon dioxide is a colorless, odorless gas with a vapor density of 1.53, heavier than air. It is the 20th most produced industrial chemical, and is used as a fire extinguishing agent, in carbonated beverages, as an aerosol propellant and in many other uses. Carbon dioxide is a liquid cryogenic (very cold) material with a boiling point of -130 degrees Fahrenheit. Carbon dioxide is non-flammable and relatively non-toxic, however, it is a simple asphyxiation hazard (will displace oxygen in the air, causing suffocation). Below is the molecular and structural formula for carbon dioxide:
Some non-metal compounds can be separated into families which have similar hazards among individual family members. These compounds are hydrocarbons and hydrocarbon derivatives. The first group we will discuss are the hydrocarbons. These compounds contain only carbon and hydrogen in their formulas. Carbon has the ability to bond with itself to satisfy its need for electrons, this happens frequently in the hydrocarbon families. The carbons form straight chained structures with particular physical and chemical characteristics. Below is an example of a straight chained hydrocarbon compound: