ChemistryChapter 5 The Periodic table

The Periodic table

• Most valuable tool to chemists

• Developed by Dimitri Mendeleev

• Originally arranged by increasing atomic mass

• Modern periodic chart is arranged by increasing atomic number

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Periodic Law

• Rows are called periods– Atomic mass and atomic number

increase across a period

• Columns are called Groups or Families– Elements in groups have the same

number of valence electrons– Elements in the same group also

have similar chemical properties

• The pattern or repeating properties is called PERIODIC LAW

Periodic Trends

• Families • Atomic Radius• Ionization energy• Electronegativity• Reactivity

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Atomic Radius

• As atomic # increases, the increasing # of protons attracts valence electrons more closely to nucleus.

• Within a period, atomic radius decreases as atomic # increases

Atomic Radius Trends

Atomic Radius DecreasesIncreases

Ionization Energy

• Energy required to remove an electron from an atom’s outer energy shell.

• In a period, IE increases as atomic # increases.

• In a group, IE decreases as atomic # increases

Ionization Energy Trends

Electronegativity

• Ability of an atom to attract electrons to itself in a compound.

• EN increases from lower left to upper right of periodic table.

• (similar to ionization energy)

Electronegativity Trends

Reactivity

• How readily a substance combines chemically w/another substance

• Elements w/out full set of valence electrons tend to react.

• Elements w/full set tend NOT to react. (Noble Gases)

Noble GasesNobleNoble

GasesGases

Classes of elements

• Metals- on left of periodic table

• Nonmetals- right

• Metalloids- in between

Titanium

Helium

Germanium