1. Chemical Periodicity

2. Chemists used properties of elements to sort them into groups
1829, J.W. Dobereiner’s classification system
-elements in triads

3. 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.

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

6. 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

7. Three Classes of Elements Metals, Nonmetals, Metalloids

8. Alkali Metals very reactive good conductors end in s1
need to lose 1e- to have noble gas configuration

9. Alkaline Earth Metals end is s2 Less reactive than alkali metals.
need to lose 2e- to have noble gas configuration

10. Halogens combine easily with alkali metals e- conf. ends in p5
need to gain 1e- to achieve noble gas configuration
“salt-formers”

11. Full outer electron shell Not likely to form compounds
Noble Gases
Full outer electron shell
Not likely to form compounds

12. Transition Metals Electrons are added to the d orbitals
Good conductors of electricity
High luster

13. Inner Transition Metals
Electrons are added to the f orbitals
Rare Earth elements

14. Blocks on the Periodic Table