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There are 90 naturally occurring and 18 man-made elements. Not all of the elements on the Periodic Table are common or particularly hazardous to responders. There are, however, some that we will call the "Hazardous Materials Elements." These elements are particularly important when studying the chemistry of hazardous materials.
Most of the hazardous materials encountered by response personnel include or are produced from these 39 elements. Hazmat personnel should become familiar with these 39 elements and be able to recognize them by symbol and name. Formulas may appear on container labels and are found in many reference books and computer data bases. Being able to recognize symbols in a formula could help responders quickly identify potential hazards. This is especially true if part of a label is missing and only the formula is visible.
Elements with 83 or more protons are radioactive; many are rare and probably will not be encountered by emergency responders. Man-made elements are the result of nuclear reactions and research. These elements may have existed naturally on earth at one time but because they are radioactive and many half-lives have passed they no longer exist naturally.
The elements on the Periodic Table can be divided into three groups: primary, transition and rare earth. Primary elements have a definite number of electrons in the outer shell. This number is equal to the number at the top of each column in the "towers" at each end of the periodic table. Transition elements may have differing numbers of electrons in the outer shell. They are located in the "valley" between the towers. Horizontal rows are called periods and are numbered from 1 to 7. Atomic numbers increase by one as you go across the periods from left to right.
An element's atomic weight is listed on the Periodic Table. Atomic weight is the sum of the weight of the protons and the neutrons located in the nucleus of an atom. All of the weight of the element occurs in the nucleus. For the purposes of "street chemistry," electrons will not have weight. Atomic weights are located on the Periodic Table above or below the symbol of an element. It is the number that is not a whole number. Location of the atomic number varies among Periodic Tables, so be sure to look for the number with the decimal point.
The other number on the Periodic Table located above or below the symbol is a whole number and is known as the atomic number. The atomic number is equal to the number of protons in the nucleus. The atomic number also equals the total number of electrons in the orbits outside the nucleus of an atom. Protons have a positive charge (+) and electrons have a negative charge (-). There must be an equal number of protons and electrons in an atom of a particular element to maintain an electrical balance. An element is identified by the number of protons, which is the atomic number. The number of protons in an element does not change. If the number of protons is changed, the result is a different element. Protons act as a kind of "social security number" to identify a specific element.
The Periodic Table is divided into two sections by a stair-stepped line. This line starts under hydrogen and goes over to boron and then stair steps down one element at a time to astatine or radon, depending on which Periodic Table is being used. Eighty-one elements to the left and below the stair-stepped line are metals. Metals make up about 75 percent of all elements. Metals lose their outer shell electrons easily to the non-metals when forming compounds. They conduct heat and electricity very well, and are malleable (can be flattened) and ductile (can be drawn into a wire). Metals are all solids except for gallium, mercury, francium and cesium, which are liquids at "normal" conditions.
The 17 elements to the right and above the line are non-metals. Non-metals have a strong tendency to gain electrons when forming a chemical bond. They may be solids, liquids or gases, and are poor conductors of heat and electricity. Solid non-metals are either hard and brittle or soft and crumbly.