The Periodic TableThe Periodic Table

A Short HistoryA Short History

End of 1700s:End of 1700s:Had identified 30 Had identified 30 elementselements

Lavoisier separated Lavoisier separated metals and nonmetalsmetals and nonmetals

Some known since prehistoric times

CuO2

Ag

Au

C

H2

N2

Early 1800Early 1800

56 known elements56 known elements

New methods such as New methods such as atomic spectra used atomic spectra used to identify new to identify new elementselements

German Chemist J.W. Dobereiner German Chemist J.W. Dobereiner (1780-1849)(1780-1849)

Observed several Observed several triadstriads

3 elements with 3 elements with similar properties similar properties where the middle where the middle element had average element had average propertiesproperties

TriadsTriadsElement Atomic Mass Density

Cl 35.5amu 1.56 g/L

Br 79.9amu 3.12 g/L

I 126.9amu 4.95 g/L

Ca 40.1amu 1.55 g/L

Sr 87.6amu 2.70 g/L

Ba 137.0amu 3.50 g/L

1865 J.A.R. Newlands (1837-1898)1865 J.A.R. Newlands (1837-1898)

62 Known elements62 Known elements

When elements were arranged When elements were arranged by increasing atomic mass, the by increasing atomic mass, the properties repeated every 8properties repeated every 8thth elementelement

Called the phenomena theCalled the phenomena the

““Law of OctavesLaw of Octaves””

1869 Russian Chemist 1869 Russian Chemist Dimitri Mendeleev (1834-1907) andDimitri Mendeleev (1834-1907) and

German Chemist Lothar Meyer (1830-1885)German Chemist Lothar Meyer (1830-1885)

Nearly identical schemes for classifyingNearly identical schemes for classifying

Mendeleev given credit because published Mendeleev given credit because published firstfirst

Produced first periodic tableProduced first periodic table

Mendeleev given credit over Newlands Mendeleev given credit over Newlands because he sometimes broke the pattern because he sometimes broke the pattern to put in order of propertiesto put in order of properties

Allowed him to predict properties of Allowed him to predict properties of missing elementsmissing elements

Led to prediction of 2 elements not yet Led to prediction of 2 elements not yet discovereddiscovered

MendeleevMendeleev

Mendeleev given credit because published Mendeleev given credit because published firstfirst

Produced first periodic tableProduced first periodic table

he sometimes broke the pattern to put in he sometimes broke the pattern to put in order of propertiesorder of properties

Allowed him to predict properties of missing Allowed him to predict properties of missing elementselements

Led to prediction of 2 elements not yet Led to prediction of 2 elements not yet discovereddiscovered

Mendeleev’s Prediction:

B C N

10.8 12.0 14.0

Al Si P

26.7 28.0 30.9

Zn

65

Cd In Sn Sb

112.4 114.8 118.7 121.8

As

74.9

Eka

Aluminum

Eka

Silicon

1913 English Chemist H.G.J. 1913 English Chemist H.G.J. MoselyMosely

Noticed that Mendeleev Noticed that Mendeleev not always correctnot always correct

Arranged elements by Arranged elements by atomic number, not atomic number, not massmass

Periodic LawPeriodic Law

When elements are arranged When elements are arranged in order of increasing atomic in order of increasing atomic number, their physical and number, their physical and chemical properties show a chemical properties show a periodic patternperiodic pattern