The Periodic Table - Organizing Elements

Many elements were unknown when the Periodic Table was first created Many elements were unknown when the Periodic Table was first created Chemists used the properties of elements to sort them into groups Chemists used the properties of elements to sort them into groups

Mendeleev’s Periodic Table Several “systems” were proposed, but none were accepted Several “systems” were proposed, but none were accepted Mendeleev wrote properties on notecards and arranged them Mendeleev wrote properties on notecards and arranged them Arranged by increasing atomic mass Arranged by increasing atomic mass Left spaces where he predicted future elements would go Left spaces where he predicted future elements would go Did not know about structure of atoms yet Did not know about structure of atoms yet

Periodic Law Elements are arranged in order of increasing atomic number (# of protons) Elements are arranged in order of increasing atomic number (# of protons) Pattern of physical/chemical properties Pattern of physical/chemical properties Periods- horizontal row Periods- horizontal row Groups- vertical column Groups- vertical column How many periods are on P.T.? How many periods are on P.T.? How many groups are on P.T.? How many groups are on P.T.?

Three Classes of Elements Metals Metals Nonmetals Nonmetals Metalloids Metalloids

Metals Good conductors of heat and electricity Good conductors of heat and electricity High luster (shiny) High luster (shiny) Solid at room temperature (except Hg-mercury) Solid at room temperature (except Hg-mercury) Ductile- used for wires Ductile- used for wires Malleable- hammered into thin sheets Malleable- hammered into thin sheets

Nonmetals Variation in properties Variation in properties Most are gases at room temperature, but a few are solids, Br is liquid Most are gases at room temperature, but a few are solids, Br is liquid Poor conductors of heat and electricity Poor conductors of heat and electricity Brittle- easily shattered Brittle- easily shattered

Metalloids Properties of both Properties of both Depends on conditions Depends on conditions