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Study Of Selected Groups Of The Periodic Table
Alkali Metals - Group IA
They are so called because they form alkalies (soluble
bases). Sodium and potassium are the sixth and seventh most
abundant of the elements, comprising, respectively, 2.6
and 2.4 percent of the Earth's crust.
Because of their high reactivity, the alkali metals are
never found as free metals in their natural state. They
generally are found combined with other elements in the
form of simple or complex compounds. The simpler compounds
of the alkali metals are soluble in water and therefore
are easily extracted and subjected to chemical operations
for purposes of separation and purification. Minerals belonging
to this class, such as halite (NaCl), sylvite
(KCl), and carnallite (KCl × MgCl2
× 6H2O), although somewhat rare, are the most important
commercial sources of the alkali metals.
The alkali metals have all of the physical properties generally
associated with metals, including silver-like lustre, high
ductility, and excellent conductivity of electricity and
heat. Lithium is the lightest metallic element.
The alkali metals are low melting, ranging from a high of
179° C for lithium to a low of 28.5° C for cesium.
Alloys of alkali metals exist that melt as low as -78°
The alkali metals are extremely reactive and combine readily
with most of the substances found in the atmosphere. (Only
lithium, however, reacts with nitrogen.) The alkali
metals all react vigorously, and often violently, with water,
releasing hydrogen and forming strong caustic solutions.
Most common non-metallic substances such as the halogens,
halogen acids, sulphur, and phosphorus react with the alkali
metals. The alkali metals themselves react with many organic
compounds, particularly those containing an active hydrogen
Alkali Earth Metals Group- II A
Prior to the 19th century, substances that were
nonmetallic, insoluble in water, and unchanged by
fire were known as earths. Those earths, like lime,
that resembled the alkalies (soda ash and potash) were designated
alkaline earths. Alkaline earths were thus distinguished
from the alkalies and from other earths, such as alumina
and the rare earths. By the early 1800s it became clear
that the earths, formerly considered to be elements, were
in fact oxides, compounds of a metal and oxygen. The metals
whose oxides make up the alkaline earths then came to be
known as the alkaline-earth metals and have been classified
in group II of the periodic table ever since Mendeleyev
proposed his first table in 1869.
The alkaline-earth metals are extremely electropositive;
that is, like the alkali metals, their atoms easily lose
electrons to become positive ions (cations). The salts are
colourless unless they include a coloured anion (negative
The oxides of the alkaline-earth metals are basic.
A fairly steady increase in electropositive character is
observed in passing from beryllium, the lightest member
of the group, to radium, the heaviest; as a result of this
trend, beryllium oxide is only weakly basic and even shows
acidic properties, whereas barium and radium oxide are strongly
basic. The metals themselves are highly reactive reducing
agents; that is, they readily give up electrons to other
substances that are, in the process, reduced.
Halogens - Group VII A
They were given the name halogen from the Greek roots
hal- (“salt”) and gen
(“to produce”), because they all produce
sodium salts of similar properties, of which sodium chloride,
table salt, is the best known.
The free halogen elements are not found in nature because
of their great reactivity. In combined form, fluorine
is the most abundant of the halogens in the Earth's crust.
The percentages of the halogens in the igneous rocks of
the Earth's crust are 0.06 fluorine, 0.031 chlorine, 0.00016
bromine, and 0.00003 iodine. Astatine does not occur in
nature because it consists only of short-lived radioactive
The halogen elements show great resemblances to one another
in their general chemical behaviour and in the properties
of their compounds with other elements. There is, however,
a progressive change in properties from fluorine through
chlorine, bromine, and iodine to astatine—the difference
between two successive elements being most pronounced with
fluorine and chlorine. Fluorine is the most reactive of
the halogens and, in fact, of all elements, and it has certain
other properties that set it apart (see below General properties
of the group).
Noble Gases - Group 0
These are so called because they have completed their octets
and have thus achieved stability. They rarely react with
any element and whenever they do so it is at high temperatures.
The term “noble” alludes to the extraordinarily
limited reactivity of the gases. They also are sometimes
called inert gases for the same reason. It was, however,
discovered in 1962 that the heavier noble gases—krypton,
xenon, and radon—can form chemical compounds with
fluorine, the strongest electron attracting of all elements.
The outer electrons of the atoms of these three gases, screened
from the nucleus by intervening electrons, are held less
firmly and can be removed.
After hydrogen, helium is the most plentiful element
in the universe, comprising almost 25 percent of its total
mass. Under ordinary conditions, the noble gases
are colourless, odourless, and non-flammable. The noble
gases absorb and give off electromagnetic radiation in a
much less complex manner than do other substances. This
absorption and emission behaviour is exploited in the use
of the gases (with the exception of highly radioactive radon)
in fluorescent lighting devices and discharge lamps. If
any of the noble gases is confined at low pressure in a
glass tube and an electrical charge is passed through it,
the gas glows. The noble gases also have very low boiling
points and melting points, which make them useful as refrigerants
in the study of matter at extremely low temperatures.