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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 have particular hazards associated with each. By understanding these family relationships, emergency responders can determine the general hazards of materials by identifying the family to which each belongs.
Photo by Robert Burke
Cyanide salts in contact with acids produce hydrogen cyanide gas, which is used in gas chambers and could be used in chemical terrorism.
This "rule of thumb" information can help first responders identify hazards of particular materials upon arrival at an incident but it does not eliminate the need to research the chemicals further before mitigation actions are taken.
The first group of compounds is known as salts. Most everyone is familiar with at least one salt that is found in almost every home and eating establishment table salt, known chemically as sodium chloride and which is used to season and cure foods.
Sodium chloride occurs naturally in the crust of the earth and in the oceans. It is made up of chlorine, which by itself is very toxic and an oxidizer, and sodium metal, an element that is air and water reactive. Once these elements are combined, a compound is formed that is neither water reactive nor very toxic. The molecular formula for the compound sodium chloride is NaCl. Sodium chloride is a major source of chlorine production, as chlorine does not exist in nature by itself.
In general, salts are water-soluble solids; most do not burn but they can be oxidizers and support combustion. Some salts are toxic and some may be water reactive. A rule when dealing with salts is "Don't touch, and keep them dry." The hazards present in a given salt family, other than the binaries, is a result of reactivity with water. Salts are made up of a metal and a non-metal element. For example, looking at table salt again, chlorine is a non-metal and sodium is a metal. This bonding process that creates a salt is referred to as an "ionic" bond.
Photo by Robert Burke
Some water-reactive salts produce toxic vapors when wet that would require emergency responders to don Level A protection.
Metals usually do not bond together. Metals that are combined are melted and mixed together to form an alloy. For example, copper and zinc are melted and mixed together to make brass. Brass is not an element and does not have a molecular formula. There is no actual chemical bond involved but rather it is just a mixture of zinc and copper.
The second major group of compounds are non-metal elements that could be referred to as the non-salts. Non-salts are solids, liquids and gases. Many non-salt compounds are flammable. For example, the non-metal carbon combines with the non-metal hydrogen to form a hydrocarbon compound. A typical hydrocarbon is methane, with the molecular formula CH4. Methane is also known as natural gas and is very flammable. Hydrocarbons and other non-salt families and compounds will be discussed in a later column.
Just as the Periodic Table of the Elements is organized into families of elements, compounds can also be placed into families. A family of materials has particular hazards associated with it. If you can recognize the family to which a material belongs from its name or formula, you should be able to determine the hazard even if you don't know any thing else about the specific chemical.
Salts have particular hazards depending on which salt family they belong to. Salt families can be divided into groups: binary salts and binary or metal oxides.
The first family of salt compounds we will discuss are the binary salts. Binary (meaning two) salts are made up of two elements: a metal and any non-metal except oxygen. Their chemical names end in "ide," such as potassium chloride. When a compound is encountered with a metal that ends in "ide," responders would know that it needs to be looked up to determine actual hazards.