Periodic Table
What is Periodic Table ?
Periodic table is arrangement of chemical elements in the form of table. According to order of their atomic number, electronic configuration or chemical properties.
Why we need Periodic Table ?
Their was more than 115 elements have been
discovered, which need to be arranged systematically.
How scientists arranged elements in Periodic Table ?
Scientists work hard to arrange elements in periodic table, today's periodic table is the result of different historical arrangements...
History of classification of elements
1.
Prout’s
Hypothesis – 1815
2.
Dobereiner’s
Triads – 1829
3.
Newland’s
Law of Octaves – 1863
4.
Lother
Meyer Curves – 1869
5.
Mendeleev’s
Periodic Table – 1869
6.
Modern
Periodic Laws of Moseley -1913
7.
Modern
Periodic Table ( of 18 columns )
Prout’s Hypothesis
According
to this hypothesis atomic mass of elements is multiple of mass of hydrogenatom. So elements are related to each other on the basis of their atomic
masses. It fails due to the reason that some elements do not have atomic mass
in whole no. (Like chlorine have atomic mass of 35.5).
Dobereiner’s Triads
According
to Dobereiner’s triads elements arranged in the group of three elements so that
atomic mass of central element is appropriate mean of 1st and 3rd
element. These groups of three elements are known as Dobereiner’s triads.
Example-
Element
Li Na K
Li Na K
Atomic Mass
7 23 39
7 23 39
Mean of Atomic Masses of 1st
and 3rd elements is (7+39)/2 =
46/2 = 23
Newland’s Law of Octaves
According to Newland’s Law of Octaves
elements arranged in the group of 8 elements and every 8th element
is similar to the 1st element.
Li
Be B C N
O F
Na Mg Al Si P S Cl
Lother Meyer Curves
In 1869, Lother Meyer derived following
conclusion by obtaining information from graph between the atomic weight at
x-axis and atomic volume at y-axis.
1.
Elements
which have similar properties found on the same position on the graph curves.
2.
All
alkali metals like Li, Na, K, Rb, Cs, and Fr found at highest peak of curve.
3.
Halogens
like F, Cl, Br and I are found on ascending portion of curve.
4.
Alkaline
earth metals like Mg, Ca, Sr, Ba and Ra are found on descending portion of
curve.
5.
Elements
which do not melt easily like Be, B, C, Al, Si, Cu etc. are found at lowest
point of curve.
On the basis of above conclusions
Lother Meyer give periodic Law:
According to Lother Meyer
periodic law – “Atomic volume of elements are periodic function of their
atomic weights”.
Periodic Table
To
classify elements a chart is prepared in which elements are arranged in rows
and columns. These elements are arranged in table in such a way that the
elements with similar properties are repeat after some intervals; also elements
with similar properties are put in same column below one another. In periodic
table vertical columns are called group while horizontal rows are called
periods. In periodic table this repetition of properties in regular interval is
known as periodicity. Read below chemistry notes of periodic table like
Mendeleev periodic table, Mosley periodic table, Modern periodic table etc.
Mendeleev’s Periodic Table
In
Mendeleev’s Periodic Table, Mendeleev classify elements according to their
atomic masses and arranged these elements in table according to their
increasing order of atomic masses.
Mendeleev’s Periodic Law
According
to Mendeleev’s Periodic Law – “Physical and chemical properties of elements are
periodic function of their atomic masses”.
Mendeleev’s Periodic Table contains
seven horizontal rows known as periods and nine vertical columns known as
groups.
Modern Periodic Table
Moseley
in 1913, after doing many experiments comes to a conclusion that the elements
should be arranged as per their atomic no. and not according to atomic masses.
As atomic no. is fundamental property of all elements of periodic table. So Mosley
gives a new law which is called is Modern Periodic Law.
Modern Periodic Law
According to Modern Periodic Law- “Physical
and Chemical properties of elements are periodic function of their atomic
numbers”.
Long Form of Periodic Table
Bohr Bury invented new periodic table,
which is called as Long Form of Periodic Table. This Long Form of Periodic
Table is also known as Modern Periodic Table.
Special features of Modern or Long Form of Periodic Table
These below are Special features of
Modern or Long Form of Periodic Table
I.
18
vertical columns known as groups.
II.
Horizontal
rows known as periods.
III.
Light
metals – These are elements of periodic table of group 1 and 2.
IV.
Heavy
metals or Transition metals - These are elements of periodic table of group 3,
4, 5, 6, 7, 8, 9, 10, 11 and 12.
V.
Non-Metals
– These are elements of periodic table of group 13, 14, 15, 16 and 17.
VI.
Zero
group – These are elements of periodic table of group 18.
