The Periodic Table

A Brief History… Greek thinkers (400 BC) used the words element and atom to describe the differences and smallest parts of matter. Lavoisier divided the few elements known in the 1700's into four classes, and then John Dalton suggested that the mass of an atom was it's most important property.

More History Mendeleyev used the periodic table show chemical periodicity and to determine properties of missing elements. Since Mendeleyev had the insight to use the periodic table as a predictive tool, he is generally credited with discovering the periodic table.

How are elements arranged? By number of protons By atomic weight By chemical properties

A row is called a period A column is called a group or family

Periodic Law When the elements are arranged in order of increasing atomic number, there is periodic pattern in their physical and chemical properties. Makes it MUCH easier to remember the chemical and chemical properties of the elements.

Elements are also arranged by groups/families Alkali Metals Alkaline Earth Metals Transition Metals Other Metals Metalloids Non-Metals Chalcogens Halogens Noble Gases Rare Earth Elements

Alkali Metals Group 1A – One valence electron Very reactive metals Do not occur freely in nature Malleable, ductile, and good conductors of heat and electricity Softer than most metals Explode if exposed to water

Alkaline Earth Metals Group 2A – 2 valence electrons Metallic elements found in second group of periodic table Also very reactive, not found freely in nature

Transition Metals Ductile and malleable Conduct electricity and heat Valence electrons present in more than one shell Iron, cobalt, and nickel are the only transition metals known to produce a magnetic field

Other Metals Ductile and malleable but not the same as transition elements Only a few exhibit variable transition states High density Opaque

Metalloids Found along the stair-step line that divides metals from non-metals Have properties of metals and non-metals Some are semi-conductors meaning they can carry electrical charge

Non-Metals Do not conduct electricity or heat well Very brittle Dull Exist as gas and solids

Chalcogens 6 valence electrons, form 2- ions Name from the Greek “ore formers,” also known as the “oxygen” group. Increase in metallic character moving down the group.

Halogens 7 valence electrons, from 1- ions Form Salts Exist in all three states of matter Very reactive

Noble Gases Considered unreactive until the 1960s Have maximum number of electrons possible for their outer shell making them stable

Rare Earth Elements Lanthanide and actinide series Many are synthetic or man made All actinides are radioactive