ch-4  Characteristics of periodic table
Ɣ There are 7 periods (horizontal row) and 18 groups (vertical column) in the
periodic table.
Ɣ All periods start with group 1 at the extreme left and extend up to group 18 at the
extreme right.
Ɣ A small table composed of 2 horizontal rows and 14 perpendicular columns is
displayed beneath the main periodic treble. It is also the part of period-6 and
period-7 of main periodic table.
Ɣ In the first period (period-1) there are only two elements, which exist in group-1
and in group-18. Similarly both the period-2 and period-3 contain 8 elements,
which exist in group-1 to group-3 and in group-13 to group-18
Ɣ Each group of every period from period-4 to period-7 is filled with elements.
Ɣ In the case of the two periods, period-4 and period-5, both have 18 elements in
18 groups. That is one element has occupied a place in every group. 
Ɣ Exception is found in of period-6 and period-7. In these case of each of them a
period has 32 elements in 18 groups. Out of them only group-3 contains 15
elements and the rest 17 groups contain one element each. In this way a total of
32 elements are arranged in these periods. 
properties of the elements.
Ɣ Properties of the elements change from left to right in the same period.
Ɣ Generally, the properties of the elements depend on their group. The physical
and chemical properties of the elements of the same group are almost similar.
Ɣ Generally, the number of electrons in the last shell of the elements is equal to
their group number.
Ɣ The number of total energy shell (orbit) of the elements is equal to their period
Various periodic laws
Scientists divided the elements invented earlier into two groups- metals and nonmetals.
The metals again are divided into two groups as relatively less reactive metals (gold, silver which are called elite metals) and more reactive metals (iron, zinc which are called
inferior metals). At the beginning of 19th century, after the invention of Dalton’s atomic
theory, a great changes were taking place in practice of chemistry. In 1829 German
scientist J. W. Doberiner gave the law of triads on the basis of the atomic mass of the
Law of Triads: The mean of the mass of the two elements is nearly the same of the
other element and the properties of the three elements are almost the same. If these three
elements are arranged according to their mass the mean of the 1st and 3rd will be the
same as that of the 2nd. The three elements are called “Doberiner Traids”
For example, the mean of the total mass of Li (7) and Potassium (39) is the same as
Sodium (23).
In 1864 English scientist John A. R. Newlands found similarities in properties of every
eighth elements by arranging the elements in the increasing order of their atomic mass.
Based on that finding he proposed the Law of Octaves.
Law of Octaves: Similarities in properties of every eighth elements are found by
arranging the elements in the increasing order of their atomic mass. This is known as the
“Law of Octaves” in periodic table.
Russian scientist Dmitri I. Mendeleev examined the chemical properties of elements and
arranged the elements invented in 1869 in the increasing order of their atomic mass and
found that the elements of same properties are placed in the same column. Based on this
he proposed the periodic law. Though there is contribution of many scientists in the
invention of periodic table, Mendeleev’s is called the father of the periodic table taking
in to account the importance of his contribution.
Mendeleev’s periodic law: If elements are arranged according to their increasing
atomic mass, their physical and chemical properties repeat periodically.
In the year 1913 Mendeleev revised his periodic law after the invention of atomic
number by scientist Henry G. J. Moseley.
Mendeleev’s revised periodic law: The physical and chemical properties of the
elements repeat periodically with their atomic number. 

In the year 1869 Mendeleev introduced modern periodic table, when the concept atomic
number did not exist. In the year 1913, scientist Henry G. J. Moseley gave the concept of
atomic number. Later on Mendeleev proposed his revised modern periodic table
incorporating the concept of atomic number. Scientist Mendeleev is honored for the
invention of modern periodic table. Because it is assumed that, if the concept of atomic
number were known, scientist Mendeleev might have used the atomic number instead of
atomic mass in his proposed periodic table. 

Determination of the position of elements in periodic table from the electronic
We have known from above that, electronic configuration is the basis of the periodic
table. That is why, position of any elements in periodic table may be assumed from the
electronic configuration of that element. Electronic configurations of some elements are
given in the table below (Table-4.2). Electron arrangement of elements in different
levels is shown. In an element the number of energy levels where electrons are
configured, is the period number of the element. For example consider the case of H and
He. In these elements electrons are arranged in only one energy level and the position of
them is in period-1of periodic table. Similarly the electrons of the elements from Na to
Ar are configured in three energy levels. So it can easily be said that the number of their
period is 3. Other than some exceptions, usually, the number of electrons at their outermost energy
level may be called the group number of that element in a certain period. Then, if we
think, we will understand that, the above rule will be applicable in the case of group-1 of
all the seven periods. That is, the number of electrons at the outermost energy level of
the elements of group-1 is 1. That is why, according to rule, the number of that group is
1. Similarly in the case of group-2 we will get the idea of group number from the
number of electrons at their outermost energy level. On the other hand, the elements
whose outermost energy level is filled with electrons are placed in group-18. In the case of period-2 and period-3, that is, the elements that have electrons configured
in two or three energy levels, elements who have 3 electron in outermost energy level is
placed in group-13. Because in the case of period-2 and period-3 there is no element
presents in group-3 to group-12. Then in the case of elements who have electron
arrangement in two to three energy levels, if the outer most energy level contains more
then two electrons, then the group number can be determined by adding ten (10) with the
number of electron present in the outermost energy level.
From period-4 to period-7 the elements that have electrons at ‘d’ sublevel, the sum of the
number of electrons at ‘d’ sublevel and the number of electrons at the outermost energy
level indicate their group number. For period-6 and period-7 the elements that have
electrons at ‘f’ sub level, are placed separately at the bottom of the main periodic table. 

Periodic properties of elements
On observation of any one period in the periodic table it is seen that the elements at the left are
metal and gradually it turns to sub metal and to nonmetal. There is Na at the extreme left end
of the period-3 which is a reactive metal. Again, Cl (2nd from right) is a reactive nonmetal. A
continuity of transformation from metal to nonmetal is observed in the elements exist between
these two. Na, Mg and Al are of metallic properties. Si is a sub metal (bears the properties of
both metal and non metal). P, S and Cl all are non metals and their melting point and boiling
point is low. In any group the physical and chemical properties of elements gradually rotates
periodically. For example, the alkali metals of group-1 are soft and have low melting point.
The melting point of the metals of this group decreases with the increase of atomic number.
From left to right of the periodic table that is from group-1 to group-17, the melting point and
boiling point increases first (up to metal) then decreases (from nonmetal). In this way the
melting point and boiling point of halogens of group-17 is much lower then the alkali metals of
group-1. In case of halogen, similar gradual changes in different physical properties are
observed. For example the melting point, boiling point and density increase with increase in
atomic number.
Besides these some important properties of elements like- atomic radius, ionization
energy, electronegativity, electron affinity etc. rotate periodically in periodic table. In a
period of periodic table atomic radius decreases from left to right and in a group atomic
radius increases from top to down. In a period of periodic table other properties except atomic radius increases from left to right (with some exceptions) with the increasing
atomic number. That is, the ionization energy of alkali metals of group-1 is low and the
ionization energy of halogens of group-17 is high. Similarly in a group of periodic table
these properties decrease from top to down with the increasing atomic number. You will
learn more about these in higher classes. 

Alkali metal: The elements of group-1 in the periodic table e.g. Li, Na, K, Rb, Cs and Fr
are called alkali metal. All these elements produce hydrogen gas and alkaline solution
when reacts with water. They form ionic compounds (salt) by donating the only electron
at the outermost energy level.
Alkaline earth metal: The elements of group-2 in periodic table from Be to Ra are
called alkaline earth metal. Its properties are almost same as that of alkali metals. Oxides
of these metal produce alkaline solutions when reacts with water. They also form ionic
compounds (salt) by donating the two electrons of the outermost energy level. These
elements exist in soil as different compounds.
Transition elements: The elements of group-3 to group-11 in periodic table are known as
transition elements. Transition elements have their own colors. They are used as metallic
substances. They form ionic compounds by donating the electrons of outermost energy level.
In a period of periodic table properties of compound of the transition metals change from
ionic character to covalent character from metals placed at the left to right.
Coinage metal: The elements of group-11 in periodic table Cu, Ag, Au have metallic
character like brightness. Historically coins were made of these metals and were used as a medium of exchange in trades and other needs. They are called coinage metals. In fact,
they are transition metal.
Halogen group: The elements of group-17 in periodic table F, Cl, Br and I, and At,
these five elements together are called halogen. The meaning of the word halogen is salt
maker. They form halide ion by receiving one electron at their outermost energy level.
The main source of halogens is the sea salt. They themselves form di-atomic molecules
by sharing electrons.
Inert gas: The elements of group-18 in periodic table are called inert gas. As their
outermost energy level is filled with sufficient electrons, they do not show any tendency
to form compound by accepting, donating or by sharing electrons. That means, they
remain inactive to form bonds or to take part in chemical reactions. 

Advantages of Periodic Table
Periodic table is an essential tool for chemistry student and applied chemist. Practice of
chemistry is not possible without modern periodic table. We have known earlier that 118
elements have identified till now. Let us consider the four physical properties of each
element e.g. melting point, boiling point, density and physical state (solid, liquid,
gaseous) and four chemical properties like- reaction with oxygen, water,
acid and base. Thus, for 118 elements 4 physical and 4 chemical properties
total in 472 properties. Is it not impossible to memorize such a large
number of properties? We also know that, the properties of elements is not
limited in 4 physical properties and 4 chemical properties. There are a large
number of similar types of physical and chemical properties There are a
large number of similar types of physical and chemical properties that we
will learn later. However it is understood that all elements of periodic table have thousands of properties and to memorize them
individually is really impossible.
We can get the idea of physical and chemical properties easily from the position of the
elements in periodic table. For example, elements of group-1 except hydrogen are called
alkali metal and it is possible to cut them by a knife. All these elements can donate the
only electron at its outermost energy level. All the elements except hydrogen react with water to form hydrogen gas. Similarly, the idea of properties of any element present in
any group can be remembered by comparing the properties with other elements of that
group. On the other hand, differences in properties of elements that exist in various
groups of the same period can be assumed by observing the surroundings i.e. by
comparing with the properties with their neighbouring elements. Considering the
physical properties of elements present in various groups of period-3 we see that, Na is
alkali metal which is a solid substance and can be cut by a knife. The physical properties
of the elements on the right side of periodic table change gradually. Even Cl and Ar
remain in gaseous state though the number of liquid elements in periodic table is small.
So we have understood that, though in relative view it is meant that the periodic table is
the arrangement of elements in a simple table but actually it has great significance. We
can say in one word that, practice in chemistry in present time is not possible without
Periodic Table.