The Periodic Table

1. The Periodic Table Chapter 5

2. History of the Periodic Table 1829 – Law of Triads, Johann Dobereiner • In a group of three elements with similar properties, the mass of the middle element is the same as the average mass of the other two elements 1864 – Law of Octaves, John Newlands • When the elements are listed in order by atomic mass, the properties of the eighth element are similar to the properties of the first element

3. 1869 – Periodic Table of Elements, Dmitri Mendeleev • When the elements are listed in order of increasing ATOMIC MASS, they form rows and columns that showed a repeating pattern of properties * This allowed for the prediction of the properties of elements not yet discovered!! 1914 – Modern Periodic Table, Henry Moseley • Moseley identified the number of protons the elements have. The elements were rearranged in order of ATOMIC NUMBER (number of protons).

4. periodic - having a regular, repeating pattern Examples: • days of the week • months of the year periodic law – The properties of the elements repeat in a predictable way when atomic numbers are used to arrange elements into groups.

5. Arrangement of the Elements *Horizontal rows on the periodic table are called periods; the atomic number (number of protons) of the elements increases from left to right *Vertical columns on the periodic table are called groups; the members of each group have similar properties Valence electrons– electrons located in the outermost energy level of an atom, 8 valence electrons is considered “full”

6. Three Classes of Elements Metals • Found to the LEFT of the zig-zag line • Contain few valence electrons • Lose electrons when form compounds • Good conductors of heat and electricity • Malleable (can be hammered into sheets) • Ductile(can be drawn into thin wires) • Shiny, most are silver

7. Nonmetals • Found to the RIGHT of the zig-zag line • Outer energy level is nearly full; noble gases have full outer energy level • Gain electrons when form compounds • Dull • Not malleable or ductile • Brittle when in solid form • Poor conductors of heat and electricity

8. Metalloids • Border the zig-zag line (B, Si, Ge, As, Sb, Te, Po and At) • Have some properties of metals and some properties of nonmetals • Semiconductors – depending on temperature • Outer energy levels are about half full • Can be shiny or dull • Usually brittle

9. Characteristics of the Groups Group 1: Alkali metals • Contain 1 valence electron • Soft - can cut with a knife • Low density • Most reactive of all metals; never found pure in nature • React violently with water Group 2: Alkaline earth metals • Contain 2 valence electrons • Very reactive, but less reactive than group 1 • Harder and more dense than group 1

10. Group 3 – group 12: Transition metals • Contain 1 or 2 valence electrons • Less reactive than groups 1 and 2 • Excellent conductors of heat and electricity • Higher densities than groups 1 and 2 Lanthanides (atomic numbers 58-71) • Part of transition metals, follow lanthanum, also known as “Rare Earths” • Reactive • Many used in alloys Actinides (atomic numbers 90-103) • Part of transition metals, follow actinium • All are radioactive (unstable) • All following plutonium (atomic number 94) are synthetic

11. Group 13 – Group 16 • Mixtures of metals, metalloids, and nonmetals • Varied reactivity • Group 13 – 3 valence electrons • Group 14 – 4 valence electrons • Group 15 – 5 valence electrons • Group 16 – 6 valence electrons • No other consistent characteristics Group 17: Halogens • Consists of all nonmetals • Contain 7 valence electrons • Most reactive nonmetals • Poor conductors of heat and electricity • React violently with Alkali metals (group 1) to form salts • Never found as pure elements in nature

12. Group 18: Noble gases • Consists of all nonmetals • Have a FULL set of valence electrons (2 electrons for helium, 8 for the rest) • Unreactive • Colorless, odorless gases at room temperature • Used in lighted signs because glow in color when electricity is run through them (neon is red, argon is lavender, helium is yellow, xenon is blue) Hydrogen • Contains 1 valence electron, so placed above group 1 (Alkali metals), but is NOT a metal • Very reactive • Reacts explosively with oxygen • Low density • Most abundant element in the universe (think stars)