Groups on the Periodic Table

Group 1 elements, which include lithium, sodium, potassium, rubidium, cesium and francium, are alkali metals. The metals in this group are so soft that they can be cut with a knife. They are also shiny, and have low density. Alkali metals are the most reactive metals and are never found in elemental form. They are found combined only with other elements. In fact these metals will explode when they come in contact with water and need to be stored in oil. Alkali metals are very reactive because they can easily give away or lose their single valence electron. Some important compounds formed with alkali metals include sodium chloride (table salt), borax (sodium tetraborate), potash (potassium carbonate), and washing soda (sodium carbonate) among others.

Group 2 elements, which include beryllium, magnesium, calcium, strontium, barium, and radium, are called alkaline-earth metals. These metals are fairly hard, shiny, and good conductors of electricity. Although alkaline-earth metals are not as reactive as alkali metals, they are still not found in elemental form, but only in compound form. They have two electrons in their valence shell and like alkali metals react readily with halogens to form salts, such as calcium chloride.

The 38 elements in Groups 3 through 12 of the periodic table are called "transition metals". Iron, copper, zinc, silver, and gold are all transition metals. As with all metals, transition metals are ductile and malleable, shiny and good conductors of heat and electricity. Because the atoms of transition metals do not give away their electrons as easily as atoms of Group 1 and 2, they are less reactive than alkali metals and alkaline-earth metals. The transition metals are unique in that their valence electrons, or the electrons they use to combine with other elements, are present in more than one shell. Also, unlike other elements, they don't always use the same number of valence electrons in chemical reactions. Iron (Fe), for example, sometimes likes to give away two electrons, and sometimes three, forming different compounds. Transition metals can be mixed with other metals to form alloys such as steel, or with calcium to form compounds found in cement.

The lanthanides and actinides, the two rows below the main part of the periodic table, are part of the transition metals group. The first row includes the lanthanides. At one time, the lanthanides were called the rare-earth elements, although they are not particularly rare. The lanthanides include the metal neodymium used as a component to make high-strength, powerful neodymium magnets. The elements in the second row are radioactive or unstable and are called actinides. Only two of the actinides, thorium and uranium, occur in nature, the others are man-made.

The Boron Group, which includes boron, aluminum, gallium, indium, and thallium, is the first group of mixed elements. The group contains one metalloid (boron) and four metals. The elements in this group have three electrons in the valence shell and are very reactive. Aluminum is the most important metal in the Boron Group. It is used to make light weight alloys used in automotive parts, foil, cans and other products. The metalloid boron is used to make the compound boric acid. Boric acid is used as a cleaning agent and is also added to Pyrex glass to make it heat resistant.

The Carbon Group includes carbon, silicon, germanium, tin, lead and flerovium (temporary name ununquadium). The properties of the Carbon Group vary greatly. In their elemental solid state, Group 14 metalloids, silicon and germanium, act as electrical semiconductors, although silicon is mainly non-metallic. Tin and lead are metals, while flerovium, also known as Element 114, is radioactive. Carbon, the fourth most abundant element on Earth, is a very important nonmetal that forms compounds in a variety of ways. When combined with oxygen, hydrogen, and trace amounts of other elements, carbon forms all the organic compounds that make up living organisms.

The Nitrogen Group includes two nonmetals: nitrogen and phosphorous; two metalloids: arsenic and antimony; and one metal: bismuth. The elements in this group have five valence electrons and generally gain three electrons when bonding with other elements. Nitrogen is a gas that makes up 80% of Earths atmosphere. Natural sources of nitrogen can be found in animal and plant proteins and in fossilized remains of ancient plant life. Nitrogen from the atmosphere can be combined with hydrogen to form ammonia, used in fertilizer production. Unlike nitrogen, phosphorus is extremely reactive and only found in compounds with other elements.

The Oxygen Group includes three nonmetals: oxygen, sulfur, and selenium; and two metalloids: tellurium, and polonium. These can be found in nature in both free and combined states. All elements of the Oxygen Group have six electrons in their outermost shell which makes this group reactive. Oxygen is the most abundant element on Earth, found in the atmosphere and dissolved in water. It is essential for the survival of most living organisms.

The Halogen Group includes four nonmetals: fluorine, chlorine, bromine, and iodine; and one metalloid: astatine. The elements in this group have seven valence electrons and are very reactive because they only need to gain one more electron to complete their outer shell. In their pure form, halogens form diatomic molecules, such as chlorine (Cl₂). Halogens combine with metals to form salts. Most halogens, such as chlorine or iodine, can be used as disinfectants.

Group 18, which includes elements helium, neon, argon, krypton, xenon, and radon, are all colorless, odorless gases at room temperature. These gases are inert, or nonreactive and do not react with other elements to form compounds because their valence shell is full. These elements can be used in gaseous form. Neon is used to make lighted signs. Helium, because its less dense than air, is used to make blimps and weather balloons float.

Hydrogen is a special element because it is not like any other group of elements. It is placed above Group 1 in the periodic table because it has one electron in its valence shell but does not belong in the alkali metals group. Hydrogen is found in stars and it is the most abundant element in the universe. However, it only makes up one percent of the Earths mass. On Earth, most hydrogen is combined with oxygen in the form of water.