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PERIODIC TABLE

Organizing the Elements• Chemists needed a way to organize all the elements and those yet to be discovered

• DOBEREINER (1829) grouped elements into TRIADS, three elements with similar properties

• NEWLANDS (1865) arranged elements in order of increasing atomic mass (properties repeated every eight elements… �LAW OF OCTAVES�)

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The First Periodic Table• MENDELEEV (1869) published the first Periodic Table

• Arranged elements in order of increasing atomic mass and similar properties

• Left spaces for undiscovered elements AND predicted the properties using his table

THE DISCOVERY OF GALLIUM AND GERMANIUM HELPED CONVINCE SCIENTISTS OF THE

IMPORTANCE OF HIS TABLE… PREDICTED PROPERTIES MATCHED THE ACTUAL PROPERTIES!!

The First Periodic Table

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Problems with the Table

• Mendeleev thought some of the atomic masses were incorrect so he broke his rules (placed Telluriumbefore Iodine due to properties)

• Atomic masses were not wrong… he just did not know yet that each element had a unique number of protons!

Periodic Law

• MOSELEY (1913) developed the Modern Periodic Table

• Arranged elements in order of increasing atomic number

Properties of elements repeat when placed in order of INCREASING atomic number

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Reading the Table• PERIOD: Row on the Periodic Table / Energy level• GROUP: Column (families) with similar physical and chemical properties

Three classes of elements on the Periodic Table…

MetalsFound on the left hand side and middle

of the table

• About 80% of elements are in this class

• High luster (shiny)

• Good conductors of heat and electricity

• Typically solids at room temperature (except Hg)

• DUCTILE: can be drawn into wires

• MALLEABLE: hammered into thin sheets

• High density and melting point

• Form cations (+)

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Metals

Metals

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NonmetalsFound on the right hand side of the

table

• No luster

• Poor conductors of heat and electricity

• Most (not all) are gases at room temp

• Low density and melting point

• Not malleable or ductile

• Brittle

• Tend to form anions (-)

Nonmetals

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Nonmetals

MetalloidsFound along the �staircase� on

the table

• Have properties of both metals and nonmetals

• Ex: B, Si, Ge, As, Sb, Te, Po, and At

• Ion formation depends on their group

Arsenic Poisoning (from H2O)

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Metalloids

Metalloids