Elements and The Periodic Table

Classification of Matter

History of the Periodic Table 330 B.C - 4 elements elements elements Chemists required a systematic method to organize the elements

Johann Dobereiner 1829 Law of Triads Groups of 3 elements with similar properties

John Alexander Newlands 1864 Arranged all known elements in order of increasing atomic mass Observed that every 8th element had similar physical and chemical properties (Law of Octaves) Began to group these elements into “families”

Julius Lothar Meyer 1865 Also arranged the elements in order of increasing atomic mass Found repeating patterns and developed a table of elements

Dimitri Mendeleev 1869 Credited as the Father of the Periodic Table Periodic Law: When arranged by atomic number, the properties of the elements repeat at regular intervals.

and the same number of valence electrons

Hydrogen (A class of it’s own) Sometimes it behaves like an alkali metal, sometimes like a halogen, and sometimes in its own unique way.

Group 1: Alkali Metals 1 valence electron (electrons in their outermost shell) Soft, shiny, easily cut with a knife The most reactive metals React violently with water (stored in oil or a vacuum) React with halogens to form salts

Group 2: Alkaline Earth Metals 2 valence electrons Light, reactive metals

Groups 3-12: Transition Metals 1 or 2 valence electrons Strong, hard metals Good conductors of heat and electricity Wide range of chemical and physical properties

Group 17: Halogens 7 valence electrons Extremely reactive nonmetals

Group 18: Noble Gases Full outer shell Extremely unreactive (inert)

Lanthanides (Rare Earth Metals) Elements 57-70

Actinides Elements Transuranic Elements: Synthetic elements (elements 93+)