• Hydrogen is the lightest element. It is by far the most abundant element in the universe and makes up about about 90% of the universe by weight. Hydrogen as water (H2O) is

absolutely essential to life and it is present in all organic compounds. Hydrogen gas was used in lighter-than-air balloons for transport but is far too dangerous because of the fire risk (Hindenburg).

• Lithium is a solid only about half as dense as water. A freshly cut chunk of lithium is silvery, but tarnishes in a minute or so in air to give a gray surface.

• Lithium is mixed (alloyed) with aluminum and magnesium for light-weight alloys, and is also used in batteries, some greases, some glasses, and in medicine.

• Pure aluminum is a silvery-white metal with many desirable characteristics. It is light, nontoxic and nonmagnetic It is easily formed, machined, and cast. Pure aluminum is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminum is an abundant element in the earth's crust, but it is not found free in nature.

Carbon is found free in nature in different forms. Two forms in takes are graphite and diamond. Graphite is one of the softest known materials while diamond is one of the hardest. Carbon is found in some meteorites. Natural diamonds are found in ancient volcanic "pipes" such as found in South Africa. Carbon is present as carbon dioxide in the atmosphere and dissolved in all natural waters. It is a component of rocks as limestone. Coal, petroleum, and natural gas are chiefly hydrocarbons. Carbon is unique among the elements in the vast number of variety of compounds it can form.

Sulfur is found in meteorites, volcanoes, hot springs, and as galena, gypsum, Epsom salts, and barite. It is recovered commercially from "salt domes" along the Gulf Coast of the USA. Jupiter's moon Io owes its colors to various forms of sulfur.

• Sulfur is a pale yellow, odorless, brittle solid, which is insoluble in water but soluble in carbon disulphide. Sulfur is essential to life. It is a minor constituent of fats, body fluids, and skeletal minerals.

• About one fifth of the atmosphere is oxygen gas. Oxygen is the third most abundant element found in the sun. Oxygen in excited states is responsible for the bright red and yellow-green colors of the aurora. About two thirds of the human body, and nine tenths of water, is oxygen. The gas is colorless, odorless, and tasteless. Liquid and solid oxygen are pale blue.

• Ozone (O3) is a form of oxygen. It is formed from electrical discharges or ultraviolet light acting on O2. It is an important component of the atmosphere which is vital in preventing harmful ultraviolet rays of the sun from reaching the earth's surface. Oxygen is very

reactive It is essential for respiration of all plants and animals and for most types of

combustion.

• Copper is one of the most important metals. Copper is reddish with a bright metallic luster. It is malleable, ductile, and a good conductor of heat and electricity (second only to silver in electrical conductivity). Its alloys, brass and bronze, are very important. Gun metals also contain copper. Apparently the reason that policemen are nicknamed "cops" or "coppers" is to do with their uniforms which used to have copper buttons.

• Chlorine is a greenish yellow gas which combines directly with nearly all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. As little as 1000 ppm is likely to be fatal after a few deep breaths. It was used as a war gas in 1915. It is not found in a free state in nature, but is found commonly as NaCl (solid or seawater).

• The metal is the seventh most abundant and makes up about 1.5 % by weight of the earth's crust. Potassium is an essential constituent for plant growth and it is found in most soils. It is also a vital element in the human diet.

• Potassium is never found free in nature. It is one of the most reactive metals and, apart from lithium, it is the least dense known metal. It is soft and easily cut with a knife. It is silvery in appearance

• It oxidizes very rapidly in air and must be stored in mineral oil. It usually catches fire during the reaction with water.

• Mercury is the only common metal liquid at ordinary temperatures. Mercury is sometimes called quicksilver. It rarely occurs free in nature. It is a heavy, silvery-white liquid metal. It is a rather poor conductor of heat as compared with other metals but is a fair conductor of electricity. It alloys easily with many metals, such as gold, silver, and tin.

• Ordinary tin is a silvery-white metal, is malleable, somewhat ductile, and has a highly crystalline structure.

• Tin resists distilled, sea, and soft tap water, but is attacked by strong acids. Oxygen accelerates the attack. It is, or was, used to plate steel, making "tin cans". Tin is used as one component in bell metals.

• Calcium is a metallic element, fifth in abundance in the earth's crust. It is an essential constituent of leaves, bones, teeth, and shells.

• The metal is a silvery color and is rather hard. It readily forms a white coating in air, reacts with water, burns with a yellow-red flame.

• Calcium does not occur free in nature. Calcium is found mostly as limestone, gypsum and fluorite. Stalagmites and stalactites contain calcium carbonate.

• Nitrogen makes up about 78% of the atmosphere by volume but the atmosphere of Mars contains less than 3% nitrogen. Its compounds are vital components of foods, fertilizers, and explosives. Nitrogen gas is colorless, odorless, and generally inert. As a liquid it is also colorless and odorless.

• When nitrogen is heated, it combines directly with magnesium, lithium, or calcium. When heated under pressure with hydrogen in the presence of a suitable catalyst , ammonia forms Nitrogen is "fixed" from the atmosphere by bacteria in the roots of certain plants such as clover. Hence the usefulness of clover in crop rotation.

• Lead is a bluish-white lustrous metal. It is very soft, highly malleable, ductile, and a relatively poor conductor of electricity. It is very resistant to corrosion but tarnishes upon exposure to air. Lead pipes bearing the insignia of Roman emperors, used as drains from the baths, are still in service. Alloys include pewter and solder. Tetraethyl lead is still used in some grades of gasoline but is being phased out on environmental grounds.

• Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Iron is a vital constituent of plant and animal life, and is the key component of hemoglobin.

• The pure metal is not often found in pure form, but is usually alloyed with carbon or other metals. The pure metal is very reactive chemically, and rapidly corrodes, especially in moist air or at elevated temperatures. Any car owner knows this. Iron metal is a silvery, lustrous metal which has important magnetic properties

• Sodium is a silvery white metal. Sodium would not normally be made in the laboratory as it is so readily available commercially.

• Sodium is present as salt (sodium chloride, NaCl) in huge quantities in underground deposits (salt mines) and seawater and other natural waters. It is easily recovered as a solid by drying.

• Magnesium is the eighth most abundant element in the earth's crust although not found in it's elemental form.

• Magnesium tarnishes slightly in air, and finely divided magnesium readily ignites upon heating in air and burns with a dazzling white flame. Normally magnesium is coated with a layer of oxide, MgO, that protects magnesium from air and water.

• Silver is somewhat rare and expensive, although not as expensive as gold. Slag dumps in Asia Minor and on islands in the Aegean Sea indicate that man learned to separate silver from lead as early as 3000 B.C. Pure silver has a brilliant white metallic luster. It is a little harder than gold and is very ductile and malleable. Pure silver has the highest electrical and thermal conductivity of all metals. Silver iodide, AgI, is (or was?) used for causing clouds to produce rain.

• Silver is stable in pure air and water. It occurs in ores including argentite, lead, lead-zinc, copper and gold found in Mexico, Peru, and the USA.