The History and Arrangement of the Periodic Table 11/09 The History and Arrangement of the Periodic Table

History of the Periodic Table 11/09 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.) 11/09 Dmitri Mendeleev (cont.) Mendeleev organized each card (element) according to its atomic mass Noticed a repeating pattern of valence numbers (1, 2, 3, 4, 5, etc.) Noticed elements fell into columns (groups or families) Noticed all elements in a column had the same valence number and showed similar physical and chemical properties.

Dmitri Mendeleev (cont.) 11/09 Dmitri Mendeleev (cont.) 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.

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11/09 Henry Moseley 1913 – Henry Moseley (English Scientist) changed the arrangement of the periodic table. Instead of by increasing atomic mass, it was arranged by increasing atomic number (# of protons).

Arrangement of the Periodic Table 11/09 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 regions: metals, nonmetals and metalloids

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Metals - 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 and other shapes High melting point Tend to lose electrons

Nonmetals - properties Elements to the right of the zigzag on the table Do not conduct heat or electricity 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

Metalloids - 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

Chemical Groups (Families) 11/09 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, bond easily with other substances (unstable and explosive) Never found alone in nature Soft, silver-white, shiny Easily lose 1 electron to form a stable +1 ion Form ionic bonds Note: Hydrogen is a nonmetal gas, and forms covalent bonds. So why is it in this Alkali Metal family?

Hydrogen is a nonmetal gas and forms covalent bonds Hydrogen is a nonmetal gas and forms covalent bonds. So why is it in the Alkali Metal family? The number of valence electrons = 1

Group/Family 2 - Alkaline Earth Metals 11/09 Group/Family 2 - Alkaline Earth Metals 2 valence electrons in outer energy level 2nd most reactive elements, bond easily with other substances, unstable Never found alone in nature Lose 2 electrons to form stable +2 ions Form ionic bonds Combine with oxygen and other non-metals in the Earth’s crust

Groups 3-12 The Transition Metals 1 or 2 valence electrons Can lose and/or share valence electrons Common metals – gold, silver & copper Form metallic bonds Unpredictable

From Metals to Nonmetals (e- in outer energy level) Group 13 Boron Group/Family 3 valence electrons Group 14 Carbon Group 4 valence electrons Group 15 Nitrogen Group 5 valence electrons Group 16 Oxygen Group 6 valence electrons Group 17 Halogen Group 7 valence electrons Group 18 Noble Gases 8 valence electrons * Helium is a Noble Gas but has a full outer shell with 2 valence e-

Rare Earth Elements (Inner Transition Metals) 11/09 Rare Earth Elements (Inner Transition Metals) First Row –Lanthanide Series - Rare Earth metals - All but one is non-radioactive Second Row – Actinide Series - Most are man-made and radioactive - Many are short-lived