U5: The History and Arrangement of the Periodic Table http://www.meta-synthesis.com/webbook/35_pt/pt.html

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

Dmitri Mendeleev – Columns = Groups/Families Noticed a repeating pattern of valence electrons (1,2,3,4,5 etc..) Noticed elements fell in to columns (groups or families) Noticed all elements in a column had the same valence electrons and showed similar physical and chemical properties.

Amazing Facts with his cards! Mendeleev left blank spaces in his table so elements would line up – he also predicted what properties the undiscovered elements would have. He predicted properties of five of these elements and their compounds. Three of these missing elements were discovered by others within 15 years. The element, atomic number 101, has been named after Mendeleev.

Mendeleev’s Periodic Table by atomic mass (with empty spaces for elements that would soon be discovered)

Henry Moseley 1913 – Henry Moseley (English Scientist) changed the arrangement of the periodic table. Instead of by increasing atomic mass , Moseley arranged the elements by increasing: atomic number (# of protons). Interesting fact: Moseley's law = the energy of x-rays emitted from an element is related to its atomic number.

II. Arrangement of the Periodic Table Systematic arrangement of the elements by atomic number and chemical properties Divided into Regions: Metals, Nonmetals and Metalloids Vertical Columns – Numbered groups/families Horizontal Rows - Periods are by amount of energy levels (1-7) or orbital shells

III. REGIONS

Metals - location, properties Elements on the left side of the table Good conductors of electricity Shiny Ductile – can be drawn into thin wires Malleable – can be hammered into thin sheets or shapes High melting point Tend to lose electrons

Nonmetals - location, properties Elements on the right of the zigzag on the table Do not conduct electricity or heat Dull in appearance, not shiny Brittle or break easily Not Ductile or Malleable (cannot be drawn into wire or hammered into sheets) Lower densities Lower melting points Tend to gain electrons or share electrons with each other

Metalloids - location, properties Elements that are found along both sides of the zigzag line (except for Al) Properties of both metals and nonmetals Semiconductors - conduct heat and electricity better than nonmetals but not as well as metals Solids Can be shiny or dull Both ductile and malleable

IV. 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 Very reactive , bonds easily with other substances (unstable and explosive) Never found alone in nature Soft, silver-white, shiny 1 valence electron in outer energy level Easily lose 1 electron to form a stable +1 ion Forms ionic bonds

Think it Over: Hydrogen is a nonmetal gas, and forms covalent bonds. So why is it in the Alkali Metal family?

Group/Family 2 - Alkaline Earth Metals 2nd most reactive elements, bond easily with other substances, unstable Never found alone in nature 2 valence electrons in outer energy level Loses 2 electrons to form stable +2 ions Forms ionic bonds

Groups 3-12 The Transition Metals Unpredictable Common metals – gold, silver & copper Can lose and/or share valence electrons Forms Metallic Bonds

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 most are radioactive - many are short-lived

From Metals to Nonmetals Group # Name Valence Electrons Bonds Region 13 Boron Family 3 Covalent Ionic (lose) Metalloids & Metals 14 Carbon Family Basis of Life 4 Metals, Metalloids Nonmetals

From Metals to Nonmetals Group # Name Valence Electrons Bonds Region 15 Nitrogen 5 Covalent Ionic (Gains) Metals, Metalloids Nonmetals 16 Oxygen 6 Covalent or Ionic (Gains electrons)

From Metals to Nonmetals Group # Name Valence Electrons Bonds Region 17 Halogen 7 Covalent or Ionic (Gains Electrons) Nonmetals Very Reactive 18 Noble Gases or Inert Gases 8* Does not bond Stable Non reactive Full outer shells * Helium has a full outer shell with 2 valence electrons

Stability Groups 1-17 are unstable The Noble Gas group/family is stable Think it Over: What makes an element stable?

Point to Ponder The element Carbon is the “Basis of Life”. What is meant by this?