The periodic table has been constructed with a view to classify them to simplify the study of the elements. Even before the modern periodic table was created, many scientists attempted to classify the elements in various ways, including Proud’s hypothesis, Dobereiner’s Triad Law, Newland’s Law of Octaves, Luther Meyer’s Atomic Volume Curve, and Mendeleev’s Periodic Table. The modern or long size periodic table is the result of the gradual modification in the efforts of these scientists.
Modern or Long Form of Periodic Table
The modern periodic table is constructed based on the distribution or electronic configuration of electrons in the atomic orbit of the Niels Bore. Hence it is also called the periodic table of Bore. It is found that the physical and chemical properties of elements are a recurring function of their electronic configuration. On the basis of this principle, Rang, Werner, and Bury created this modern or longitudinal or amplified periodic table, hence it is also called the periodic table of Bore-Bury.
The Structure of the Modern Periodic Table:
a) Periods and Groups of the Modern Periodic Table:
There are 7 horizontal rows in this periodic table called Periods, their names and the number of elements in them are as follows:
The number of elements in period and types of the period:
No of period No. elements in period Types of period
1 2 very short period
2 8 short period
3 8 short period
4 18 long period
5 18 long period
6 32 very long periods
7 32 very long periods
The modern periodic table has 18 vertical groups whose name and the number of elements in them are as follows:
|No. of group||Name of group||No. of elements||No. of group||Name of group||No. of elements|
These include elements of class 1 as Alkali metals, class 2 elements as Alkaline Soil metals, class 15 elements as Pnicogen, class 16 elements as Chalcogen, class 17 elements as Halogen, and class 18 elements as Inert Gas.
b) Classification of Elements in the Periodic Table based on Electronic Configuration:
Based on the electronic configuration, the elements are divided into four blocks in the periodic table. These are called s, p, d, and f respectively.
Elements of s-block:
Elements whose last electrons are in the s orbitals are called elements of s block. These elements are placed in group 1 and group 2. The electronic configuration of their last shell is ns1 or ns2. They have a valency of 1 or 2. All are soft metals and have very low melting and boiling points. They are all conductors of electricity and heat.
Elements of p-Block:
Elements whose last electrons are in the p orbitals are called elements of the p block. Elements from groups 13 to 18 are elements of the p block. The electronic configuration of their final shell is ns2np1-6. It can be all three metals, non-metal, and nonmetal. They have high electronic negativity.
Elements of d-Block:
Elements whose last electrons are in the d orbitals are called elements of the d block. In the periodic table, they are placed in the group 3 to 12 between the s and p blocks. They are also called Transition Elements because their d orbitals are incomplete. . However, they are not considered to be Transition Elements due to fulfillment of d orbitals of Zn, Cd, and Hg present in the 12th group.
Elements of f-block:
Elements whose last electrons are in the inner orbitals (n-2)f are called elements of the f block. They are placed in the 3rd group of the sixth and seventh periods in the periodic table. These are also known as Internal Transition Elements. These are shown below separately due to the lack of space in the periodic table. Elements of the sixth period are called Lanthanides or Rare Earth Elements and elements of the seventh period are called Actinides or Transuranic Elements.