The vertical columns are called groups. Basically there
are eight groups (1 to VIII) but each group is further
sub-divided into "A" and "B",
The elements of sub-group 'A' are called
as the properties of these elements are represented by
The element of sub-group B' are called
because the properties of these elements show a gradual
change or transition between the two sets of
representative elements, on either side of them.
Elements of a group have similar valency shell
configuration hence have similar properties.
The group number indicates the total number of electrons
in valency shell of that element.
Group IA (The Alkali Metals) or (Lithium Family)
This group includes Lithium (Li), Sodium (Na), Potassium
(K), Rubidium (Rb), Caesium (Cs) and Francium (Fr).
Their valence shell contains one electron only, and on
reaction they lose this electron and form univalent
positive ions (MI+), they are highly reactive metals
with low melting points. Fr is radioactive.
Their atomic radii, atomic volumes, ionic radii increase
from Li to Cs due to the addition of extra shell to each
element and due to same reason, the melting and boiling
points decrease downward. They are called
because they form water soluble base such as NaOH and
Group IIA (The Alkaline Earth Metals); (Beryllium
It includes Beryllium (Be) Magnesium (Mg), Calcium (Ca),
Strontium (Sr), Barium (Ba) and Radium (Ra).
Their valence shell contains two electrons. On reaction
they lose these two electrons and form divalent positive
ions (M2+). Ra is radioactive.
These elements are a bit harder, having higher melting
and boiling points than the alkali metals, but they have
smaller atomic, ionic radii and atomic volumes.
Down the group they do not show a regular trend in
melting, boiling points and densities.
Group III A (The Boron Family):
It includes Boron (B); Aluminum (Al); Gallium (Ga);
Indium (In) and Thallium (Tl). Their valency shell
contains three electrons. They exhibit a valency of 3+
and form M3+ ions. Except boron they are highly
electropositive, elements i.e. having metallic character
which increases down the group; due to increase in
atomic volume. Boron is
A metalloid is an element which has some properties of
metals and some properties of non-metals.
Group IVA (Carbon Family):
It includes Carbon (C); Silicon (Si); Germanium (Ge),
Tin (Sn) and Lead (Pb).
Their valence shell contains four electrons. C, Si and
Ge form covalent compounds whereas Sn and Pb exhibit a
variable valence of 2 and 4.
Of these elements C is non-metal; Si and Ge are
metalloids, Sn and Pb are metals.
Down the group atomic radii and volumes increase due to
addition of a new shell and for the same reason metallic
character increases down the
Group. C and Sn exist in different allotropic forms.
Group V (Nitrogen Family):
It includes Nitrogen (N), Phosphorus (P) Arsenic (As),
Antimony (Sb) and Bismuth (Bi).
Of these elements N and P are non-metals, as and Sb are
metalloids and Bi is a metal. Their valence shells
contain five electrons. There is a large variation of
properties as we go down the group.
Nitrogen exists as diatomic molecules (N2)
and forms a number of oxides as NO, N2O, NO2,
NO4 and N2O5 Due to
small atomic size and large ionization potential,
nitrogen has a tendency to accept three electrons to
form nitride ion (N3). Phosphorus exists as P4
Except Nitrogen all exist in more than one allotropic
Group VI (Oxygen Family):
It includes oxygen (O); Sulphur (S); Selenium (Se),
Tellurium (Te) and Polonium (Po).
Of these oxygen and sulphur are non-metals, selenium,
tellurium are metalloids and polonium is metal.
All of the elements exhibit the property of allotropy.
Allotropic forms of oxygen are oxygen (O2)
and ozone (O3).
Oxygen and sulphur form divalent negative ions O2-
and S2- Their valence shell contains six
Group VIIA (The Halogens):
It includes Fluorine (F); Chlorine (CI); Bromine (Br);
Iodine (I) and Astatine (-At).
Except Astatine (which is a metalloid) all others are
non-metals and exist as diatomic molecules. At room
temperature F2 and Cl2 are gases;
bromine is a liquid and iodine is a solid. Their valence
shell contains seven electrons. They have high
ionization energies and large negative electron
affinities hence they easily accept an electron to form
halide ions (x)1- i.e. (F1-Cl1-,
Group VIIIA (Inert or Noble Gases):
It includes Helium (He); Neon (Ne); Argon (Ar), Krypton
(Kr); Xenon (Xe) and Radon (Rn).
Their valence shell contains eight electrons, except
helium which has two electrons. With the exception of
krypton and xenon (which have large atomic volumes so
slightly reactive under drastic conditions) the rest of
these elements are totally inert chemically. The reason
is that these have completely filled outer shells, a
condition that represents greater stability.
INTERESTING TO NOTE
Discovery of Noble Gases
None of the noble gases was known when Mendeleev
proposed his periodic table. In 1892. The English
scientist Ramsay became interested in the discovery that
nitrogen obtained from the air had a slightly higher
density than that prepared by chemical reactions. After
careful investigation, he concluded that higher density
must be due to the presence of unknown gas. When he
separated this gas from the air, he found that it was
completely uncreative. He called it argon, the 'idle or
lazy" gas in Greek in the same year Ramsay isolated
helium (He) the lightest of all noble gases, from
uranium ores. During 1898 Ramsay and Rayleigh isolated
three additional noble gases from air, neon (Ne) krypton
(Kr) and xenon (Xe).
Group IB To VIIIB (Transition Elements):
These are metals. In these elements, besides the valence
shell penultimate shell is also incomplete. In chemical
reactions they show more than one valencies. These
elements in compounds having characteristic colours.
The total classification can be summarized in the