The periodic table of elements is organized from the lightest elements, those with a low atomic number, to the heaviest elements. The lightest element has an atomic number of one, and as the elements get heavier, their atomic numbers increase. The lightest elements are at the beginning on the periodic table.
Hydrogen is the lightest and the most plentiful element in the universe. Hydrogen, denoted by the symbol H, has an atomic number of one and joins with many other elements to produce water, ammonia, hydrocarbons, acids and bases. Hydrogen has an atomic weight of 1.008. It can act as a halogen and is also similar to alkali metals. Hydrogen is one of the cornerstone elements of the make up of the universe.
Helium is the second lightest element and is also the second most plentiful element in the universe although it's not found in large quantities on Earth. Helium, denoted by the atomic symbol He and the atomic number two, has an atomic weight of 4.0026. Helium is created underground as a byproduct of radioactive decomposition. It is used to make things, like balloons or blimps, float; it's also used as a displacement medium for gas in deep-sea diving and as a super coolant.
Lithium, the third lightest element in the periodic table of elements and the lightest metal, has an atomic number of three, an atomic weight of 6.939 and is denoted by the atomic symbol Li. This reactive metal is whitish silver in color. Lithium melts at 179 degrees Celsius or about 354.2 degrees Fahrenheit. Lithium was discovered in 1817 by John Arfvedson. The word "lithium" comes from the Greek word "lithos," which means stone.
Beryllium is a rigid, brittle, steel gray, nonmagnetic metal that does not corrode. Beryllium, denoted by the symbol Be, is the fourth lightest element and has an atomic number of 4. The atomic weight of beryllium is 9.0122. Beryllium is commonly used in aerospace engineering and in nuclear reactors. It is often combined with copper to produce metal springs and contacts for electrical mechanisms. Beryllium is both toxic and carcinogenic.