Background

Elements

Elements are the primary substance from which all other materials are built. A substance that cannot be broken down into simpler substances by chemical means is called an element. Over 100 different elements have been identified. Most of these elements exist on the earth in different amounts. Gold, silver, oxygen, and sodium are just of few of the many important elements that you may already be familiar with. The periodic table provides a visual representation and listing of the known elements. The smallest part of an element that still has all of the properties of the element is an atom.

Compounds

A compound is a pure substance that is composed of two or more elements that have been chemically joined. A compound can only be broken down into its elements by chemical means. Water, sugar, table salt, and carbon dioxide are just a few of the compounds that you might have experienced in your life. The smallest part of a compound that still has all of the properties of the compound is a molecule.

Chemical symbols

Scientists can get just as tired writing out element names as you do, so they created a shorter way of representing elements. Chemical symbols provide a shorthand way of writing the name of an element. Examples include "O" the symbol for oxygen, "N" for nitrogen, and "Mg" for magnesium. The periodic table provides a list of the chemical symbols and element names.

Chemical formulas

Compounds need a form of short-hand just like elements do, so chemical formulas were created to save ink in writing out long names. A chemical formula states the number and kind of each element present in one molecule of a compound. For instance, sucrose (table sugar) has the chemical formula of C₁₂H₂₂O₁₁. This means that three different elements are present in sugar: carbon (C), hydrogen (H), and oxygen (O). The number 12 just to the right of the "C" in the formula states that one molecule of sugar has 12 atoms of carbon (C). Each sugar molecule also has 22 atoms of hydrogen (H) and 11 atoms of oxygen (O). These numbers, 12, 22, and 11 are called subscripts. Subscripts appear to the right and a little bit lower than the element that the subscript goes with. If no number appears to the right of an element, the subscript is assumed to be one.

Law of Definite Proportions

Fancy words for a simple concept. This law states that a pure sample of a compound will always have the same proportion by mass of the elements from which it is formed. In others words, any sample of pure water on Earth or in the universe would have the same chemical formula, H2O. This states that for every one oxygen atom, there needs to be two hydrogen atoms to form the compound called water. For instance, if a substance had the chemical formula H2O2, it wouldn't be water. In fact, this compound is hydrogen peroxide, which is a chemical used to bleach hair blond.

Periodic Table

The periodic table provides a visual representation by the grouping of elements by common physical and chemical properties. The periodic table has elements arranged by increasing atomic number. Over the years, a number of scientists have added insights and ideas to the currently used versions of the periodic table.

Families (groups)

The vertical columns (going up and down) on the periodic table are called families. Families contain elements with similar chemical and physical properties. The periodic table has 18 families.

An easy way to find out how many electrons the element has in its outer level is to simply look at the family number. For instance, lithium and sodium are in the IA family and they each have one electron in the outer level. Oxygen is a VIA, so all oxygen atoms have six electrons in their outer level.

Periods (rows)

The horizontal rows (going from one side to the other side) on the periodic table are called periods. Periods contain elements that tend to have more different chemical and physical properties as the distance separating the elements on the periodic table increases. The periodic table has seven periods.