WELCOME PARADISE
VALLEY CC STUDENTS:
THIS IS YOUR "KNOW YOUR ELEMENTS"
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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.
CARBON
ELECTRON CONFIGURATION: 1s2,
2s2, 2p2
Symbol C, element that is crucial to the existence of living organisms,
and that has many important industrial applications. The atomic number
of carbon is 6; the element is in group 14 of the periodic table.
Its atomic mass is 12.01115.
The three forms of elemental carbon that occur
in nature-diamond, graphite, and amorphous carbon-are solids with extremely
high melting points and are insoluble in all solvents at ordinary temperatures.
The physical properties of the three forms differ widely because of the
differences in crystalline structure. In diamond, the hardest material
known, each atom is linked to four other atoms in a three-dimensional framework,
whereas graphite consists of weakly bonded plane layers of atoms that are
arranged in hexagons.
Carbon has the unique ability to link with other
carbon atoms to form complex chains and rings. This property leads to an
almost infinite number of carbon compounds, the most common being those
containing carbon and hydrogen. The first carbon compounds were identified
in living matter in the beginning of the 19th century, and therefore the
study of carbon compounds was called "organic" chemistry.
At normal temperatures carbon is characterized
by a low reactivity. At high temperatures it reacts directly with most
metals to form carbides, and with oxygen to form carbon monoxide
(CO) and carbon dioxide (CO2). Carbon in the form of coke
is used to remove oxygen from metal oxide ores in order to obtain the
pure metal. Carbon also forms compounds with most of the nonmetallic elements.
Carbon is a widely distributed element in nature;
it occurs there mostly in the form of carbonates. Carbon dioxide is an
important constituent of the atmosphere and is the main source of carbon
incorporated in living matter. Plants, through the process of photo-synthesis,
convert carbon dioxide into organic carbon compounds, which are subsequently
consumed by other organisms. THIS IS ONE OF THE MOST IMPORTANT BIOCHEMICAL
REACTIONS THAT OCCURS ON EARTH.
The most common isotope of carbon is carbon-12; in 1961 this isotope
was chosen to replace the isotope oxygen-16 as the standard for atomic
weights, and was assigned the atomic weight of 12.
This web site was created from materials taken from Encarta Encyclopedia
96 from Microsoft.