Alkali Metals Essay, Research Paper
The six chemical elements that are known as alkali metals are lithium (Li), sodium
(Na), potassium (K), rubidium (Rb), cesium (Cs), and the extremely rare radioactive
substance called francium (Fr). Cesium and Francium are the most reactive elements in
this group. The word alkali comes from the Arabic word al-qili, meaning plant ashes.
Plant
ashes were the first source of alkali metal compounds. The alkali metals occupy the first
column of the periodic table of the elements. Since these metals are all in the same group
on the periodic table of the elements they all have similar qualities. They all have a nS1
electron configuration. They do not occur freely in nature. They are softer than other
metals, and have lower melting points and densities. They are all silver-white in color,
they
are all malleable, ductile, and very good at conducting heat and electricity. All of the
alkali
metals have one electron in their outer most energy level so they all bond easily. All of the
alkali metals also react violently with water. In the laboratory pure alkali metals are
generally stored in oil to prevent them from forming compounds with other elements. The
oil also prevents water vapor in the air from reaching the metals. Compounds of alkali
metals rank among the most common and most useful of all chemicals. Millions of tons of
alkali metal salts are used by industry each year. The salts come from mines and wells.
Sodium and potassium salts are raw materials for sodium hydroxide and potassium
hydroxide. These alkali metal compounds and others made from them are used in making
glass, paper, soap, and textiles; in refining petroleum; and in preparing leather.
Lithium is the lightest of the solid elements, this soft, white metal is found in minerals
such
as petalite and spodumene. The word Lithium comes from the Greek word ?lithos?
meaning ?stone?. Large deposits are found in North Carolina, Nevada, and California. It
imparts a crimson color to flame and floats on water. Chemically active, its compounds
have many uses, including lithium carbonate in treating manic-depressive psychosis. Other
compounds are used as thickeners in lubricating greases, as brines for refrigerating and
air-conditioning systems, and in dry cells and storage batteries. It was discovered in 1817
by Johan August Arfwedson. Lithium is a low density solid only about half as dense as
water. A freshly cut lithium chunk is silvery but it tarnishes in a minute or so in air to give
a
gray surface.
Life could not exist without compounds of sodium. These compounds hold water in body
tissues, and a severe deficiency of sodium can cause death. Blood contains sodium
compounds in solution. Sodium compounds are used in industry in the manufacture of
chemicals and pharmaceuticals, in metallurgy, in sodium vapor lamps, and in the
production of hundreds of everyday products. One of the most common sodium
compounds is table salt, or sodium chloride (NaCl). In its pure form sodium is a
silver-white, soft and waxy metallic element. Another important compound is sodium
bicarbonate, or baking soda. It is the sixth most abundant element on Earth and occurs in
more than trace amounts in the stars and sun. Pure sodium is used in the manufacture of
tetraethyl lead and as a cooling agent in nuclear reactors. Sodium hydroxide is used in the
manufacture of soap, rayon, and paper; in oil refining; and in the textile and rubber
industries.
Potassium is the seventh most abundant element in the Earth’s crust, potassium occurs in
many silicate rocks and minerals. The major commercial source is salt deposits, but a
small
fraction is obtained from plant and animal sources. Water-soluble potassium compounds
are economically recovered. They are frequently found as dry mineral deposits and as
brines. Most potassium is present in insoluble minerals, making it difficult to obtain, but it
can be prepared commercially by electrolysis from some refinable minerals. Potassium
compounds are used in fertilizers, soaps, explosives, glass, baking powder, tanning, and
water purification. It exists as three natural isotopes, with atomic mass numbers 39, 40,
and 41. Potassium-40 is radioactive. The most abundant isotope is potassium-39.
Rubidium is the second most reactive metal, this element is very soft and silvery-white
and
was named for the two red lines of its spectrum. Found in the minerals lepidolite,
pollucite,
and others, it is used in photoelectric cells and as a “getter” in electron tubes to scavenge
for traces of unwanted gases. It is a widely distributed element that occurs in small
amounts
in many minerals and in certain mineral waters. It is also found in small quantities in tea,
coffee, tobacco, and other plants. It was discovered in 1861 by Robert Bunsen and Gustav
Kirchhoff.
Cesium is a silvery-white alkali metal used in television cameras, atomic clocks, and as a
“getter” in electron tubes to clear out traces of unwanted oxygen in the sealed tube. One of
only three metals that are liquid at room temperature, cesium occurs in the minerals
pollucite and lepidolite in the Earth’s crust. It was the first element to be discovered
spectroscopically. Because it emits electrons when exposed to light, cesium is used in
photoelectric cells. The radioactive isotope cesium-137, which is produced by nuclear
fission, emits more energy than radium and is used in medical and industrial research as an
isotopic tracer. Commercial cesium usually contains rubidium, with which it usually
occurs
in minerals and which resembles it so closely that no effort is made to separate them.
Robert Bunsen and Gustav Kirchhoff discovered it in 1860 and named it for the unique
blue lines of its spectrum.
Francium is the heaviest member of alkali metals group in periodic table. Found in
uranium minerals, even though there is less than 1 ounce of francium in the Earth’s crust at
any one time. It can be made artificially by bombarding thorium with protons. There are
20
known isotopes. Its isotopes range in atomic weight from 204 to 224. Francium is
produced when the radioactive element actinium disintegrates. The longest-lived isotope,
francium-223, oractinium-K, has a half-life of 22 minutes. It was discovered in 1939 by
Marguerite Perey of the Curie Institute.