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The molecules of solids are packed together very closely in an organized pattern. Because the molecules are packed tightly together, they can vibrate only very gently in a very small space. This is why a solid maintains a definite size and shape until heated. When particles are this close together, they attract each other and it takes a lot of energy to pull them apart. When a solid is heated, the molecules start to vibrate faster and they eventually pull apart.
The molecules of a liquid are farther apart than those of a solid but are still attracted to each other. They are not arranged in a regular pattern. Liquids do not have a shape of their own so they conform to the shape of the container in which they are placed. When a liquid like gasoline is poured into a lawn mower engine fuel tank, it conforms to the shape of the tank. When gasoline is pumped into a gasoline tanker, it conforms to the shape of the tanker.
Molecules of a gas move rapidly and are not attracted to each other. Gases have no definite shape of their own and conform to the space or container in which they are placed. If a balloon is filled with helium, the helium takes on the shape of the balloon.
Hazardous materials may undergo both chemical and physical changes. A chemical change involves a reaction that alters the composition of the substance, and thereby its chemical identity. Chemical properties include: reactivity, stability, corrosivity, toxicity and oxidation potential.
New compounds may be formed which may have different characteristics than the compounds or elements used to make them up. Chlorine, for example, is a poison gas; sodium is a reactive metal. When they are combined, they form sodium chloride, which is neither a poison nor a reactive chemical it is table salt! Physical changes involve alterations of the physical state of the chemical but do not produce a new substance; for example, the physical transformation from a liquid to a gas or a liquid to a solid. Physical properties include: specific gravity, vapor pressure, boiling point, vapor density, melting point, solubility, flash point, fire point, autoignition temperature, flammable range, heat content, pH, and TLV and PEL.
The basics of chemistry cannot be discussed without looking at the Periodic Table of Elements. The properties of elements repeat in a regular way when the elements are arranged by increasing atomic number. This is known as periodicity.
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 the tendency of their properties to repeat at regular intervals. All chemicals are derived from elements or combinations of elements from the periodic table.
Symbols are used on the table to represent each of the elements. The Periodic Table is composed of a series of blocks representing each element. Within each block is a symbol which represents the name of that element. The symbol is a type of shorthand for the element's name. For example, the element gold is represented by the symbol Au, chlorine is Cl and potassium is K. Each symbol represents one atom of that element. The symbols may be a single letter or two letters together. A single letter is 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 is the symbol for the element cobalt two totally different materials with quite different hazards.
The symbols and names of the elements are derived from a number of sources. They may have been named for the person who discovered the element. For example, the symbol for tungsten is W, for Wolfram, its discoverer. Other elements are named for famous scientists, universities, cities and states. Es is the symbol for Einsteinium, named for Albert Ein-stein. Cm is the symbol for Curium, named for Marie Curie. Bk is the symbol for Berkelium, named for the city of Berkeley, CA. 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. Au, the symbol for gold, comes from aurum, meaning "shining down" in Latin. Cu (copper) is from the Latin cuprum or cyprium because the Roman source for copper was the island of Cyprus. Fe (iron) is from the Latin ferrum. Rubidium means red in color. Mercury is sometimes referred to as quicksilver. Sulfur is referred to as brimstone in the Bible.