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HYDROGEN
(Greek for “water former”), symbol H, reactive, colorless, odorless, and tasteless gaseous element. The atomic number of hydrogen is 1. The element is usually classed in group 1 (or Ia) of the periodic table. Like most gaseous elements, hydrogen is diatomic (its molecules contain two atoms), but it dissociates into free atoms at high temperatures.

ELECTRON CONFIGURATION: 1s1
     Free hydrogen is found only in very small traces in the atmosphere, but solar and stellar spectra show that it is abundant in the sun and other stars, and is, in fact, the most common element in the universe. In combination with other elements it is widely distributed on the earth, where the most important and abundant compound of hydrogen is water, H2O. It is a component of all the constituents of living matter as well as of many minerals.
    It forms an essential part of all hydrocarbons and a vast variety of other organic substances. All acids contain hydrogen; the distinguishing characteristic of an acid is its dissociation, upon going in.to solution, to yield hydrogen ions.
    The lightest in weight of all gases, hydrogen has been used for the inflation of balloons and dirigibles. It ignites very easily, however, a small spark causing it to burn, and several dirigibles, including the Hindenburg, have been destroyed by hydrogen fires. Helium, which has 92 percent of the lifting power of hydrogen and is not inflammable, is used whenever possible.
    Hydrogen is known to exist in three isotopic forms. The nucleus of each atom of ordinary hydrogen is composed of one proton. Deuterium, present in ordinary hydrogen to the extent of 0.02 percent, contains one proton and one neutron in the nucleus of each atom and has an atomic mass of two. Tritium, an unstable, radioactive isotope, contains one proton and two neutrons in the nucleus of each atom, and has an atomic mass of three and constitutes only 1 in 1018 atoms of hydrogen.

HELIUM
(Greek helios, "sun"), symbol He, inert, colorless, odorless gaseous element. In group 18  of the periodic table.  Helium is one of the noble gases. The atomic number of helium is 2. The atomic weight of helium is 4.003.


ELECTRON CONFIGURATION:  1s2

The French astronomer Pierre Janssen discovered helium in the spectrum of the corona of the sun during an eclipse in 1868. Helium is the second most abundant element in the universe, after hydrogen.
    Helium has monatomic molecules, and is the lightest of all gases except hydrogen. . Helium, like the other noble gases, is chemically inert. Its single electron shell is filled, making possible reactions with other elements extremely difficult and the resulting compounds quite unstable. Helium is the most difficult of all gases to liquefy and is impossible to solidify at normal atmospheric pressures. These properties make liquid helium extremely useful as a refrigerant and for experimental work in producing and measuring temperatures close to absolute zero. Liquid helium can be cooled almost to absolute zero at normal pressure by rapid removal of the vapor above the liquid. At a temperature slightly above absolute zero, it is transformed into helium II, also called superfluid helium, a liquid with unique physical properties. It has no freezing point, and its viscosity is apparently zero; it passes readily through minute cracks and pores and will even creep up the sides and over the lip of a container. Helium-3, the lighter helium isotope of mass 3, which has an even lower boiling point than ordinary helium, exhibits markedly different properties when liquefied.
    Because it is noncombustible, helium is preferred to hydrogen as the lifting gas in lighter-than-air balloons; it has 92 percent of the lifting power of hydrogen, although it weighs twice as much. Helium is used to pressurize and stiffen the structure of rockets before takeoff and to pressurize the tanks of liquid hydrogen or other fuel in order to force fuel into the rocket engines. It is useful for this application because it remains a gas even at the low temperature of liquid hydrogen. A potential use of helium is as a heat-transfer medium in nuclear reactors because it remains chemically inert and nonradioactive under the conditions that exist within the reactors.
THINK ABOUT HELIUM'S CHEMICAL INERTNESS IN TERMS OF ITS HAVING ITS FIRST PRINCIPAL ENERGY LEVEL OR SHELL FILLED.  DOES THIS ELEMENT NEED TO TAKE OR DONATE ELECTRONS?

LITHIUM
Symbol Li, silvery white, chemically reactive metallic element that is the lightest in weight of all metals. In group 1 (or Ia) of the periodic table. Lithium is one of the alkali metals. The atomic number of lithium is 3.


ELECTRON CONFIGURATION: 1s2, 2s1

Chemically, lithium resembles sodium in its behavior in that both have an np1 valence electron. They form 1+ cations. It does not occur in nature in the free state but only in compounds, which are widely distributed.  Important compounds of lithium include the hydroxide, used for bonding carbon dioxide in the ventilator systems of spacecraft and submarines; and the hydride, used to inflate lifeboats.  Lithium carbonate, a common mineral, is used in the treatment of manic-depressive psychosis (principle component of psycho-active drugs such as Valium).

BERYLLIUM
Symbol Be, gray, brittle metallic element, with an atomic number of 4. It is in group 2 (or IIa) of the periodic table . Its atomic weight is 9.012.


ELECTRON CONFIGURATION: 1s2, 2s2

Beryllium, one of the alkaline earth metals.  It forms 2+ cations.
    The addition of beryllium to some alloys often results in products that have high heat resistance, improved corrosion resistance, greater hardness, greater insulating properties, and better casting qualities. Many parts of supersonic aircraft are made of beryllium alloys because of their lightness, stiffness, and dimensional stability.