"Street Chemistry" Part 2

Each symbol for an element on the Periodic Table of Elements represents one atom of that particular element. The atom is the smallest part that any element can be divided into by normal means. It is atoms of elements that combine together to form...


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Photo by Robert Burke
Jet fuel is a mixture of several compounds.

Atoms are electrically neutral so they must have an equal number of protons and electrons so that the positive and negative charges balance each other out. The atom is held together by the strong attraction between the positive protons and the negative electrons. This is an example of the fact that opposite charges attract.

Just as the atom is the smallest part of an element, a single element is the smallest portion of a chemical compound. Chemical compounds are made up of two or more elements covalently or ionicly bonded together. Chemical compounds are represented by formulas much like elements are represented by symbols. The formula for a compound is much like a recipe, it tells how many atoms of each element must be bonded together to make a particular compound.

According to the Condensed Chemical Dictionary, "a formula is a written representation using symbols of a chemical entity or relationship." There are three kinds of chemical formulas: empirical, molecular and structural.

An empirical formula indicates the composition of the relative number and the kind of atoms in a molecule of a compound. For example, CH is the empirical formula for both acetylene and benzene. The molecular formula shows the actual number and kind of atoms in a chemical compound. The molecular formula for hydrochloric acid is HCl, one atom of hydrogen and one atom of chlorine. Anytime there is only one atom of an element, no subscript numbers are used.

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Photo by Robert Burke
Elemental argon from family eight on the Periodic Table is chemically inert. It is often shipped as a cryogenic liquid which is very cold and when it gives off gases becomes an asphyxiation hazard.

The structural formula of a compound indicates the location of the atoms in relation to each other in a molecule as well as the number and location of chemical bonds. The following illustration is an example of a chemical structure for the compound butyric acid which has a molecular formula of C3H7COOH:

The molecular formula is most likely to be encountered by emergency responders. It may be found in reference books, on Material Safety Data Sheet (MSDS) reports and on container labels. By looking at the formulation of the compound, the responder may be able to predict potential hazards of a material. Certain elements present in compounds may represent a particular family of hazardous materials. Families of hazardous materials have particular hazards associated with them. While it is important and necessary for responders to use several reference sources to positively identify the types of compounds and their hazards, "street chemistry" can start you in the right direction.

Chemical Compounds

Two basic groups of chemical compounds are formed from elements. They are salts and non-salts. Salts are made up of a metal and a non-metal. Salts are solids and generally do not burn. There are however, some exceptions. For example, when the non-metal chlorine (Cl) is combined with the metal sodium (Na) the salt compound sodium chloride (table salt) is formed with the molecular formula NaCl. Salt compounds and their families have certain hazards and will be discussed in detail in a later article.

Metals generally do not bond together. Metals that are combined are melted and mixed together to form an alloy, in which the metals do not react chemically. For example, copper and zinc are melted and mixed together to make brass, which is not an element. No chemical bond is involved.

When the outer shell electrons of a metal are given up to a non-metal element, a salt compound is formed through a chemical bond. The outer shell of the metal is now empty so the next shell becomes the outer shell. This shell will have two or eight electrons, which is a stable configuration, just like the noble gases of family eight on the Periodic Table. The metal is then stable and electrically satisfied. The non-metal receives the electrons from the metal and now has eight electrons in its outer shell. The non-metal is now stable and electrically satisfied. The result is that a compound is formed that usually has different characteristics and hazards than the elements used to make it up.