Periodic Table of Elements

Chemistry cannot be discussed without examining the Periodic Table of Elements (Figure 3.18). The periodic table is chemistry's method of organizing everything that is known about the chemical universe on one piece of paper. The table reveals the relationship between elements by showing

Figure 3.18 Periodic table of elements.

the tendency of their properties to repeat at regular intervals. All chemical compounds are derived from two or more elements or combinations of elements from the periodic table.

Elements

Elements are the building blocks of chemical compounds. Symbols are used to represent each of the elements on the table. The periodic table is composed of a series of blocks representing each element. Within each block is a symbol that represents the name of that element. Also within the block is the atomic number (Figure 3.19) and atomic weight (Figure 3.20). The symbol is a type of shorthand for the element's name. For example, carbon has a symbol of C, the element gold is represented by the symbol Au, chlorine's symbol is Cl and potassium's symbol is K. Each symbol represents one atom of that element. Symbols may be a single letter or two letters together. Single letters are always capitalized. When there are two letters, the first is capitalized and the second is always lowercase. This is important to understand when trying to identify elements and compounds. For example, CO is the molecular formula for the compound carbon monoxide; Co, on the other hand, is the symbol for the element cobalt. There are two totally different materials with quite different hazards.

Symbols and names of elements are derived from a number of sources. They may have been named after the person who discovered the element.

Figure 3.19 C indicates the symbol for the element carbon. Numbers with decimal point indicate the atomic weight of one atom of that element.

Figure 3.20 The whole number indicates the atomic number of that element.

For example, W which is the symbol for tungsten is named after Wolfram, the discoverer. Other elements are named after famous scientists, universities, cities and states. Es is the symbol for einsteinium, named after Albert Einstein. Cm is the symbol for curium, named after Madam Curie. Bk is the symbol for berkelium, named after the city of Berkeley, California. Cf is the symbol for the element californium, named after the state of California. Other element names come from Latin, German, Greek and English languages. In the case of sodium, Na comes from the Latin word for natrium. Au, the symbol for gold, comes from aurum, meaning "shining down" in Latin. Cu (copper) comes from the Latin cuprum or cyprium because the Roman source for copper was the island of Cyprus. Fe (iron) comes from the Latin ferrum. Bromine means "stinch" in Greek. Rubidium means red in color. Mercury is sometimes referred to as quick silver. Sulfur is referred to as brimstone in the Bible.

Studying the makeup of chemical compounds can help responders to understand the hazards and identify the materials in the field. Not all of the elements on the periodic table are common or particularly hazardous

Figure 3.21 There are 38 elements on the periodic table, that we will call the "Hazmat Elements."

to responders. Hazardous compounds are made up of one or more of approximately 40 "Hazmat Elements" from the periodic table (Figure 3.21). These elements are the building blocks of chemical compounds that are hazardous and are important when studying applied chemistry. Most hazardous materials that will be encountered by response personnel include or are produced from these 40 elements.

Hazardous materials personnel should become familiar with these elements and be able to recognize them by symbol and name. Formulas may appear on container labels, MSDS Sheets, literature, reference books and computer data bases. The ability to recognize symbols in a formula could help responders identify chemical families and potential hazards. Elements with atomic number 83 or above are radioactive; many are rare and probably will not be encountered by emergency responders. Manmade elements are the result of nuclear reactions and research. These elements may have existed on earth at one time, but because they are radioactive and many half-lives have passed, they no longer exist naturally.

Elements can be hazardous materials by themselves such as hydrogen, chlorine, potassium, uranium and others. These are considered pure chemicals rather than compounds. 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 HONCIBrIF, pronounced honk-le-brif, which includes the elemental symbol for each of the diatomic elements. Oxygen is commonly referred to as 0₂ in emergency response. This reference to 0₂ is primarily because oxygen is a diatomic element. Two oxygen atoms have covalently bonded together and act as one unit.

Chemical compounds are further organized into chemical families based upon the types of building blocks used to make them up. This chemical family relationship can determine the hazards of a chemical family, which can assist in the identification process. Family effect occurs based upon the types and numbers of elements that make up the family members. That is why it is important to be able to recognize the elements on the periodic table and in a compound, which may be hazardous based upon the type of elements present.

Hazmatology Point: A periodic table should be a resource available to hazardous materials responders as a reference tool. Periodic tables can be useful on computers and in hard copy to write notes on during an identification process.