Transcript Element PowerPoint

Hydrogen and Helium:
Unique among elements for 2 reasons
99% of Universe
(76% H2 and 23% He)
They can occupy 2 columns
Hydrogen – group 1 and 17
Helium – group 2 and 18
Hydrogen was prepared many years before it was
recognized as a distinct substance by Cavendish in
1766. It was given its name by Lavoisier in 1783.
The name is derived from the Greek words, hydro
and genes, meaning water forming; the symbol H is
derived from the name.
Hydrogen is the most abundant element in the
universe
Hydrogen:
Liquid H2 is used as a fuel in the Space Shuttle.
Liquid hydrogen is important in cryogenics and in the study of superconductivity as its boiling point is only a few degrees above absolute zero.
Great quantities of hydrogen are required commercially for the fixation of
nitrogen from the air in the Haber ammonia process and for the
hydrogenation of fats and oils. It is also used in large quantities in methanol
production, in hydrodealkylation, hydrocracking, and hydrodesulfurization.
It is used as a rocket fuel, for welding, for production of hydrochloric acid,
for the reduction of metallic ores, and for filling balloons. At one time
hydrogen was used for dirigibles (blimps), but because it is
inflammable,(think Hindenburg) the inert gas helium is preferred.
Production in the U.S. alone now amounts to hundreds of millions of cubic
feet per day.
Helium:
The element was discovered by Ramsay in 1896.
The name is from the Greek word, helios, for the sun since the evidence of the
existence of helium was first obtained by Janssen during the solar eclipse of 1868.
He detected a new yellow line in the solar spectrum. Lockyer and Frankland
suggested the name helium for the new element after determining that the spectral
line was due to a previously unknown element.
The helium content of the atmosphere is about 1 part in 200,000. However, the
element is chemically inert, forming no true compounds.
Helium is widely used:
• as an inert gas shield for arc welding;
• as a lifting gas for balloons and blimps (being much safer than hydrogen);
• as a protective gas in growing silicon and germanium crystals and in titanium and
zirconium production;
• as a cooling medium for super-conducting magnets;
• as the medium in He-Ne lasers;
• as a gas for supersonic wind tunnels.
A mixture of 80% helium and 20% oxygen is used as an artificial atmosphere for
divers and others working under pressure. Since helium is less soluble in the blood
than nitrogen and does not produce the "bends," a painful condition caused by the
formation of bubbles of gas in the bloodstream when a diver comes to the surface
Alkali Metals: Group 1 or IA
Soft, low melting points, low density, very
reactive with water both in liquid form and
in the air. (must store in oil)
Oxidation occurs quickly when exposed to
oxygen.
Lithium: