…was invented in 1869 by DmitriMendeleev.

Arrangement

• Arranged in order of increasing atomic number (was originally by increasing atomic mass, but it didn’t work!)

Classes of elements…

Metals – shiny, malleable (bendable),

good conductors

Classes of elements…

Nonmetals – usually dull, poor conductors, brittle solids or gases

Classes of elements…

Metalloids – act somewhere in between metals and nonmetals

Classes of elements…

Inert gases – also called noble gases. Totally unreactive.

Periods• The horizontal rows on the periodic table

• show the number of electron shells in the atom

• Properties such as melting point, density, and size of the atom increase across periods

1

23

4

56

7

Groups• The vertical columns on the periodic table

• The elements in a group all behave in the same

way.

Alkali MetalsAlkaline

Earth

Metals

Boron Group

Carbon GroupNitrogen Group

Oxygen GroupHalogens

Inert Gases

Transition Metals

Group 1 – Alkali metals

• Extremely reactive

• They have 1 electron in

the outer shell

• Low density

• Lithium, sodium, and

potassium

Group 2 – Alkaline Earth metals

• Also reactive

• Have 2 electrons in the

outer shell

• Slightly denser than alkali

metals

Group 3-12 – Transition metals

• – less reactive than groups 1 and 2

• 1-2 outer shell electrons

• Shiny, high density, higher melting point

• Good conductors of heat and electricity

Other Groups…

• Group 13 – Boron Group– 3 outer shell electrons

• Group 14 – Carbon Group– 4 outer shell electrons

– Carbon is the major element found in living things.

• Group 15 – Nitrogen Group– 5 outer shell electrons

• Group 16 – Oxygen Group– 6 outer shell electrons

• Group 17 – Halogens– 7 outer shell electrons

– Extremely reactive

• Group 18 – Inert Gases– Complete outer shell makes them

unreactive

– 8 outer shell electrons

13 14 15 16 17

18

Hydrogen

• Does not belong to a group.

• Behaves like either a halogen or an alkali

metal.