Chemical Periodicity

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 Elements Metals, 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”

Full outer electron shell Not likely to form compounds 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