5. DISCOVERY OF ELEMENTS IN DIFFERENT TIMES
YEAR DISCOVERED ELEMENTS TOTAL NUMBER
BEFORE 1750 C, P, S, Fe, Co, Zn, As, Ag, Au, Cu,
Sn, Sb, Pt, Hg, Pb, Bi
16
1751-75 H, N, O, F, Cl, Mn, Ni, Ba 24
1776-1800 Be, Ti, Cr, Y, Zr, Mo, Te, W, U, Sr 34
1801-25 Li, B, Na, Mg, Al, Si, K, Ca, Ce, Nb,
Rh, Cd, Pd, R, Ce, Ta, Os, Pr
52
1826-50 V, Bi, Ru, La, Th, Er, Th 59
1851-75 Rb, Pn, Cs, TI, Ga 64
1876-1900 He, Ne, Ar, Sc, Ge, Kr, Xe, Pr, Nd,
Sm, Gd, Du, Ho, Tu, Yb, Po, Ra, Ac,
Rn
83
1901-1925 Eu, Lu, Hf, Be, Pa 88
1926-1950 Tc, Pm, Af, Fr, Np, Pu, Am, Cm, Bk,
Cf
98
1951-75 Es, Fm, Md, No, Lm, Rf, Db, Sg 106
After 1975 Bh, Hs, Mt, Ds, Rg, Cu, 5 elements
without name.
117
6. To classify elements various Scientists
put forward a number of methods in
different period.
7. ARISTOTLE (BC 3 8 4 - 3 2 2 )
Four Elements Theory
(earth, air, water & fire
are the basic
constituent of matter)
8. ANTOINE LAVOSIERE ( 1 7 8 9 )
He classified 33 elements then
known into 4 groups.
5 gases – O2, H2, N2, Light,
Thermojen (heat)
17 metals – Sb, Ag, As, Bi, Co,
Cu, Sn, Fe, Mn, Hg, Mo, Ni,
Au, Pt, Pb, W, Zn
6 non metals – S, P, Coal, Cl, F, B
5 earth – lime, Mg, Berilta,
Alumina, Silica
9. JOHN DALTON (1808)
In his method relative
atomic mass of elements
are calculated.
10. PROUST ( 1 8 1 6 )
Proust’s Hypothesis – He
tried to found the relation
between atomic mass of
elements & their
characteristics.He proposed
that, all elements are
formed as combination of
Hydrogen atoms. But later
studies discarded this
theory.
11. DOBEREINER ( 1 7 8 0 - 1 8 4 9 )
Law of triads – He classified
elements into a group of 3 on
the basis of similarities of
properties. He named them
as triads.
Eg: Li 7
Na 23
K 39
12. JOHN NEWLANDS ( 1 8 6 4 )
Law of Octaves – Each
eight element had similar
properties as those of the
first, when the elements
were arranged in the
ascending order of their
atomic Masses.
Eg: H Li Be B C N O
F Na Mg Al Si P S
Cl K Ca
13. LOTHAR MEYER ( 1 8 6 9 )
He introduce Atomic Volume Curve
He tries to study the physical
characteristics of elements from
this graph.
14. DMITRI IVANOVICH MENDELEEV
( 1 8 6 9 )
In AD 1869, Mendeleev carried out
a detailed study of all the 63
elements which were then known,
And prepared separate cards for all
elements containing details such
as their names, atomic masses and
properties.
