The History and Arrangement of the Periodic Table

History of the Periodic Table 1869 – Dmitri Mendeleev (Russian Chemist) thought elements may have something in common. Organized the elements into a table Made each element a card and listed its properties known at the time (mass, density, color, melting point and valence number).

Dmitri Mendeleev (cont.) Mendeleev organized each card (element) according to its atomic mass (mass #) Noticed a repeating pattern of valence numbers (1,2,3,4,5 etc..) Noticed elements fell in to columns (groups) Noticed all elements in a column had the same valence number and showed similar physical and chemical properties.

Henry Moseley Mendeleev left blank spaces in his table so elements would line up – he also predicted what properties the undiscovered elements would have. 1913 – Henry Moseley (English Scientist) changed the arrangement of the periodic table. Instead of by increasing atomic mass (mass #), it was arranged by increasing: atomic number (# of protons).

Arrangement of the Periodic Table Systematic arrangement of the elements Arranged by atomic number and properties Numbered groups / families are in vertical columns Periods are by amount of energy levels in horizontal rows (1-7) Divided into metals, nonmetals and metalloids

Metals - properties Elements that begin at the left side of the periodic table Good conductors of electricity Shiny Ductile – can be drawn into thin wires Malleable – can be hammered into thin sheets and other shapes High melting point Tend to loose electrons

Nonmetals - properties Elements that are to the right of the zigzag on the periodic table Not shiny, dull in appearance Do not conduct heat or electricity Are brittle and break easily Cannot be drawn into wire or hammered into sheets Lower densities Lower melting points Tend to gain electrons

Metalloids - properties Elements that are found along both sides of the zigzag line Solids Can be shiny or dull conduct heat and electricity better than nonmetals but not as well as metals Both ductile and malleable

Chemical Groups (Families) Elements that are in the same group or family (column) of the Periodic Table have similar properties because they have the same number of valence electrons

Group (Family) 1 - Alkali Metals 1 valence electron in outer energy level Very reactive substances so it easily bonds with other substances Easily loses 1 electron to form a stable +1 ion (ionic bond) Never found alone in nature Soft, silver-white, shiny

Group (Family) 2 - Alkaline Earth Metals 2 valence electrons in outer energy level Loses 2 electrons to form +2 ions Second most reactive elements but not as reactive as group #1, so bonds easily with other substances Never found alone in nature Will always bond ionically in nature Found combined with oxygen and other non-metals in the Earth’ crust

Groups 3-12 The Transition Metals 1 or 2 valence electrons Can lose and or share valence electrons Can have many multiple electrons in 2nd to last energy levels Common metals – gold, silver & copper The U.S. imports at least 60 of these types of elements which are strategic and vital for our economy

From Metals to Nonmetals (outer energy level) Group 13 – Boron Group/Family 3 valence electrons - metalloids and metals in group - usually bonds covalently Group 14 Carbon Group 4 valence electrons - non-metals, metals and metalloids - will always bond covalently ( electron sharing) - contain elements which are essential for cell functions

- will always bond covalently Group 15 Nitrogen Group 5 valence electrons - non-metals, metalloids and metals - will always bond covalently Group 16 Oxygen Group 6 valence electrons - will bond covalently and ionically in nature Group 17 Halogen Group 7 valence electrons - all non-metals that are very reactive and form compounds called halides ( salts) - bonds covalently and ionically

- colorless Group 18 Noble Gases 8 valence electrons - non-reactive ( inert ) / very stable - have a full outer shell filled with electrons - non-metals

Rare Earth Elements (Inner Transition Metals) First Row – Lanthanide Series - naturally found rare Earth metals - all but one is non-radioactive Second Row – Actinide Series - most are man-made and radioactive - many are short-lived