ChemicalPeriodicity

• Chemists used properties of elements to sort them into groups

• 1829, J.W. Dobereiner’s classification system -elements in triads

Dmitri Mendeleev• In 1869, Mendeleev’s table based on

increasing atomic mass.• Later same year, Lothar Meyer published a

very similar table• Elements with similar chemical properties are

in the same column.• Provided space for elements unknown at the

time.

• In 1913, Henry Moseley identified an atomic number for each known element.•Modern periodic table

arranged by atomic number

The Periodic Law• Elements in a group have similar properties• Properties of elements in a period change as

you move left to right• Pattern of properties in a period repeats as

you move from one period to the next• When elements are arranged in

order of increasing atomic number, there is a periodic repetition of their physical and chemical properties

Three Classes of ElementsMetals, Nonmetals, Metalloids

Alkali Metals• very reactive• good

conductors• end in s1

• need to lose 1e- to have noble gas configuration

Alkaline Earth Metals

• end is s2

• Less reactive than alkali metals.

• need to lose 2e- to have noble gas configuration

Halogens• combine easily

with alkali metals

• e- conf. ends in p5

• need to gain 1e- to achieve noble gas configuration

• “salt-formers”

Noble Gases

• Full outer electron shell• Not likely to

form compounds

Transition Metals

• Electrons are added to the d orbitals• Good

conductors of electricity• High luster

Inner Transition Metals• Electrons are

added to the f orbitals• Rare Earth

elements

Blocks on the Periodic Table