The Periodic Table…an arrangement of elements according to similarities in properties.

Development Dimitri Mendeleev, 1834 - 1907 first periodic table   first periodic table organized elements into columns by increasing atomic mass left blank spaces for undiscovered elements

70 elements had been discovered mid-1800s 70 elements had been discovered  

determined the atomic number of elements Henry Moseley, 1913   created the modern periodic table determined the atomic number of elements used the atomic number instead of atomic mass to organize the periodic table 

Periodic Law When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

Basic Organization Periods horizontal rows numbered 1 – 7 bottom two rows, inner transition elements

Groups or Families vertical columns similar properties within each group 18 in total

Main Sections Representative elements groups 1, 2, 13 – 18

Transition elements groups 3 – 12 all metals

Inner transition elements bottom two rows lanthanoid series, #57 – 71 actinoid series, #89 – 103 (all are radioactive)

Metals 80% of all elements left side of periodic table (except for hydrogen) 80% of all elements ductile (stretched into wire) AND malleable (flattened into thin sheets) luster all but one solid at room temperature, 20C (Hg only metal liquid at room temp.) good conductors of heat and electricity high densities, high boiling points and melting points

= METALS

Nonmetals right side of periodic table poor conductors of heat and electricity solids and gases at room temp. (Br only liquid at room temp.) not malleable or ductile brittle no luster, dull low densities, low boiling and melting points

= NONMETALS

Metalloids properties between those of metals and nonmetals on stair step line EXCEPT for ALUMINUM, Al (B, Si, Ge, As, Sb, Te, Po) properties between those of metals and nonmetals all are solids at room temperature

= METALLOIDS

Group Names Group 1 ALKALI Metals most reactive group, react violently with water 1 electron in the outer shell very soft , can be cut with a knife

Group 2 ALKALINE EARTH Metals 2 electrons in outer shell

Group 17 HALOGENS “salt-makers” 7 electrons in outer shell individually poisonous, but in a compound they are harmless

Group 18 NOBLE GASES INERT gases/nonreactive (do not react) with other elements 8 electrons in their outer shell