The periodic table is the tabular arrangement of elements, according to their atomic number, to study the periodic behavior of their physical and chemical properties. It is a symbol of chemistry but is widely used in physics and all other sciences. It tells us that when elements are arranged in order of increasing atomic number, their properties are repeated. In this article, we will discuss the history, structure, and trends of the periodic table.
History
The history of the periodic table is as follows:
NAME OF SCIENTIST
YEAR
CONTRIBUTION
AL-RAZI
9th Century
Divided all substances into four categories:
· Vegetable
· Animal
· Derivative
· Mineral
His classification is based on the physical and chemical properties of substances.
DOBEREINER
1829
Arranged elements known at that time into Triads.
JOHN NEWLANDS
1863-64
Arranged elements in
increasing order of atomic weights.
Proposed Law of Octaves
LOTHAR MEYER
1864
Plotted atomic masses vertically and atomic volumes horizontally to arrange elements.
DMITRI MENDELEEV
1871
Presented FIRST REGULAR PERIODIC TABLE
ANTONIUS VAN DEN BROEK
1911
Gave hypothesis of atomic number.
HENRY MOSELEY
1911
Discovered atomic number experimentally by using X-ray spectroscopy.
After the discovery of atomic number, the periodic table was rearranged and atomic mass was replaced with atomic number which was a major improvement in Mendeelev’s periodic table and it leads us to the Modern periodic table.
MODERN PERIODIC TABLE
The essential features of the periodic table are given below.
Groups and periods
Families
Blocks
Metals, Non-metals and Metalloids
GROUPS AND PERIODS
The periodic table is divided into vertical columns called groups and horizontal rows called periods.
Differentiation between the two of them is given below:
GROUPS
PERIODS
Vertical columns in the periodic table
Horizontal rows in the periodic table
8 groups in the periodic table.
7 rows in the periodic table.
Each group is divided into two subgroups i.e A and B
Periods are numbered in Arabic numerals i.e 1 to 7
Elements in A subgroups =Normal elements( IA to VIA)
Elements in B subgroups =Transition elements( IB to VIIIB)
Elements in periods are arranged as follows:
· Period 1=shortest period=2 elements
· Period 2 ,3=short periods=8 elements each
· Period 4,5=long periods=18 elements each
· Period 6,7=very long periods=32 elements in 6th one
Ø 7th period is incomplete yet contains 32 elements.
Elements in one group possess similar properties.
Elements in one period possess entirely different properties.
Groups are numbered in Roman numerals.
6th period consists of Lanthanides.
7th period consists of Actinides.
FAMILIES IN THE PERIODIC TABLE
Following are the families of the periodic table.
FAMILY NAME
GROUP NO. or ELEMENTS
ALKALI METAL
GROUP IA
ALKALINE EARTH METAL
GROUP IIA
TRANSITION METALS
GROUP IB to VIIIB
NON METALS
Upper elements of GROUP IVA TO VIA
HALOGENS
GROUP VIIA
NOBLE GASES
GROUP VIIIA
METALLOIDS
SOME ELEMENTS OF GROUP IIIA to VIA
BLOCKS
The periodic table comprises of four blocks.
s block
Group IA and IIA elements
p block
Elements of group IA to VIIIA
Except Helium
d block
Transition Elements
f block
Inner transition elements
METALS, METALS AND METALLOIDS
A list of metals, nonmetals, and metalloids is given below:
SUBSTANCE
ELEMENTS
METALS
All other elements except non-metals and metalloids
NONMETALS
H, He, C, N, P, O, S, Se, F, Cl, Br, I and noble gases(17 elements)
METALLOIDS
B, Si, Ge, As, Sb, Te, Po (7 elements)
TRENDS IN THE PERIODIC TABLE
Chemical properties of elements tend to vary steadily along the group or period. Hence
some common trends of physical properties varying in the periodic table are given below:
