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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 compounds of hazardous materials that responders will commonly encounter.
Photo by Robert Burke
The physical state of an element or compound is one of the factors that determines the appropriate level of chemical protective clothing.
Some elements do not exist naturally as single atoms. They chemically bond with another atom of that same element to form "diatomic" molecules. The term "di" simply means two and atomic refers to the atom. Therefore, diatomic means two atoms. The diatomic elements are hydrogen, oxygen, nitrogen, chlorine, bromine, iodine and fluorine.
One way of remembering the diatomic elements is by using the acronym HONClBrIF, pronounced honk-le-brif, which includes the elemental symbol for each of the diatomic elements. Oxygen is commonly referred to as O2 in emergency response. This reference to O2 is primarily because oxygen is a diatomic element. Two oxygen atoms have covalently bonded together and act as one unit. The means of chemical bonding will be discussed later in this article.
Much can be learned about a compound by looking at its elemental composition. For example, generally, chemicals that contain chlorine in their formula may be toxic to some degree because chlorine is toxic. As with many rules of chemistry, there are exceptions, such as sodium chloride (NaCl) table salt. Even if you didn't know that sodium chloride is table salt and treated it as a toxic material, your error would be on the side of safety. If you are going to make errors when dealing with hazardous materials, always make sure you err on the side of safety. You may get chewed out afterwards by your officer or take some ribbing from other responders but no one has ever died from embarrassment! On the other hand, if you are not cautious and your errors are not on the side of safety, your actions could be fatal.
An atom is the smallest particle of an element that can be found that retains all of its elemental characteristics. The word atom comes from the Greek, meaning "not cut." For example, take a sheet of paper and tear the paper in half. Keep tearing the paper in half until it becomes so small that it cannot be torn any smaller by hand. Then take a knife and cut the paper into smaller pieces. Eventually, it will not be able to be cut any smaller. The atom is like that last piece of paper.
Photo by Robert Burke
Chlorine in its elemental form is toxic, an inhalation hazard and a strong oxidizer.
You cannot have a smaller piece of an element than an atom. A single atom cannot be altered chemically. To create a smaller part of an element would require that the atom be split in a nuclear reaction. Therefore, a single atom is the smallest particle of an element that would normally be encountered. Many elements, both diatomic and regular, are hazardous materials in their elemental state. Examples are chlorine, phosphorus, oxygen, molten sulfur, arsenic and sodium metal. Responders, however, are more likely to encounter combinations of elements that have formed compounds.
The atom is comprised of three major parts: electrons, which have a negative (-) charge; protons, which have a positive (+) charge; and neutrons, which are neutral. The atom is like a miniature solar system with the nucleus in the center and the electrons orbiting around the outside. These parts are referred to as subatomic particles because they are smaller than the atom itself.
The electrons are most important to chemistry and the nucleus is most important to radioactivity. Orbiting in shells or energy levels around the nucleus are varying numbers of electrons. Electrons are very important in discussing chemistry for hazardous materials responders. The outer shell electrons are where the chemical bonding takes place. The elements bond and form compounds to become stable. That is so that each atom of each element will become like the noble gases in family eight of the Periodic Table, which are chemically inert.