"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
Phosphorus in its elemental form is air reactive and spontaneously ignites when exposed to air. It is shipped under water.

The second group of compounds is made up totally of non-metal elements. The non-metals are comprised of two or more non-metal elements combining to form a compound. For example, the non-metal carbon combines with the non-metal hydrogen to form a hydrocarbon. A typical hydrocarbon might be methane with the molecular formula CH4. Hydrocarbons will be discussed further in another article.

Non-metals may be solids, liquids or gases. They may burn as well as being toxic, explosive, corrosive and oxidizers. The hazardous materials most frequently encountered by emergency responders are compounds made up of just a few non-metal materials. They are carbon, hydrogen, oxygen, sulfur, nitrogen, phosphorus, fluorine, chlorine, bromine and iodine. In elemental form and in compounds, these elements make up the bulk of hazardous materials encountered by emergency responders.

Chemical bonding, in the case of non-metals, involves electrons that are shared between the non-metal elements. This process of sharing electrons is called covalent bonding. Approximately 90% of covalently bonded hazardous materials are made up of carbon, hydrogen and oxygen. The remaining 10% are composed of chlorine, nitrogen, fluorine, bromine, iodine, sulfur and phosphorus. It is still necessary that each atom of each element have two or eight electrons in the outer shell. However, there is no exchange of electrons. When the bonding takes place, each atom of each element brings along their electrons and shares them with the other elements.

A chemical compound becomes electrically stable through the process of sharing and exchanging electrons. The fact that compounds have become electrically stable does not mean they are no longer hazardous. Quite simply, elements combine and chemical reactions occur so that compounds can become electrically stable. These combinations of elements that form compounds create many new hazardous and non-hazardous chemicals.

Emergency responders may encounter elemental chemicals that are hazardous when released in an accident. However, most of the hazardous chemicals encountered will be in the form of compounds or mixtures. Compounds and mixtures have a broad range of hazards, including explosive, corrosive, flammable, toxic and oxidizers.

Covalently bonded compounds also have specific families based upon the types of elements present. These families have particular hazards associated with them. The covalently bonded hazardous materials families will be discussed in a later article.

Mixtures

Chemical compounds may also exist in the form of mixtures. A mixture is two or more compounds combined together without any chemical bonding taking place. Each of the compounds retains its own characteristic properties.

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Photo by Robert Burke
Acetylene is highly unstable and is soluble in acetone. When it is dissolved in acetone, it becomes relatively stable.

The two types of mixtures are homogeneous and heterogeneous. Homogeneous means "the same kind" in Latin. In a homogenous mixture, every part is exactly like every other part. For example, water has a molecular formula of H2O. Pure water is homogeneous; it contains no substances other then hydrogen and oxygen. Loosely translated to include mixtures, homogeneous refers to two or more compounds or elements that are uniformly dispersed in each other. A solution is another example of a homogeneous mixture.

Heterogeneous means "different kinds" in Latin. In a heterogeneous mixture, the different parts of the mixture have different properties. The components in a heterogeneous mixture can be separated mechanically into their component parts. Examples of heterogeneous mixtures are gasoline, the air we breathe, blood and mayonnaise.