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PHYSICAL SCIENCE

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PERIODIC TABLE

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

DISCOVERY OF ELEMENTS IN DIFFERENT TIMES

To classify elements various Scientists put forward a number of methods in different

period.

ARISTOTLE (BC 384-322)

Four Elements Theory (earth, air, water & fire are the basic constituent of matter)

ANTOINE LAVOSIERE (1789)

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

JOHN DALTON (1808)

In his method relative atomic mass of elements are calculated.

PROUST (1816)

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.

DOBEREINER (1780-1849)

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 7Na 23K 39

JOHN NEWLANDS (1864)

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

LOTHAR MEYER (1869)

He introduce Atomic Volume Curve

He tries to study the physical characteristics of elements from this graph.

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.

DMITRI IVANOVICH MENDELEEV’sPERIODIC TABLE

HENTRY MOSELEY (1913)

Moseley modified Mendeleev’s periodic table according to the atomic number of elements.

MODERN PERIODIC TABLE

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