Periodic Properties of the Elements Chapter 7 Periodic Properties of the Elements

Development of the Periodic Table Mendeleev – 1869 Moseley - 1913

Electron Shells and Sizes of Atoms Electron Shell = Energy Level Atomic Radii Increase top to bottom Decrease left to right

Ionization Energy Energy required to remove an electron from the ground state of a gaseous atom/ion First – Second – Third : increases Periodic Trend Decreases top to bottom Increases left to right Representative elements have greater IE than transition metals

Electron Affinities Energy change that occurs when an electron is added to one atom of the element in the gaseous state “ how easy an element gains electrons” Trend Becomes less negative from top to bottom Becomes more negative from left to right Noble Gases ΔE > 0

Metals, Nonmetals, and Metalloids Approx. 78% Metals, 15% Nonmetals, 7% Metalloids Metallic properties Shiny luster, conduct heat/electricity, malleable, ductile, solids at room temp., low IE, lose electrons in chem. Rxn, transition metals form more than one cation Nonmetallic properties Non-lustrous, poor conductors of heat/electricity, low melting points, many are diatomic, tend to gain electrons Metalloid Some like metals-some like nonmetals, some are semi-conductors

Group Trends for Active Metals: Group 1 Alkali Metals General Properties Soft metals Silvery, metallic luster high thermal/electrical conductivity low density/melting point (increase as you move down group) very reactive metals +1 ions colored flames Reactions M + Water = metal hydroxide + hydrogen M + Oxygen = metal oxides, peroxides, superoxides

Group Trends for Active Metals: Group 2 Alkaline Earth Metals General Properties Solids with typical metallic properties Harder, more dense, higher melting points as compared to Group 1 Less reactive than Group 1; reactivity increases top to bottom 2+ ions Form colorless or white compounds Colored flames

Flame Color – Reactive Metals Group 1 Lithium – Crimson Red Sodium – Yellow Potassium – Blue-Violet Rubidium – Pinkish Violet Cesium – Pinkish Violet Group 2 Calcium – Yellowish Brick Red Strontium – Deep Dark Red Barium – Yellow-green

Hydrogen Colorless diatomic gas Insoluble in water Lightest of all gases Three isotopes 1H, 2H, 3H Burns in air to form water (not highly reactive) Reacts with nonmetals to form molecular compounds Reacts with metals to form metallic hydrides

Group 6A: Oxygen Group Group changes from nonmetal gas to metalloids to metal Oxygen found naturally in two forms – O2 and O3 Sulfur forms several allotropes

Group 7A: Halogens Name means “salt formers” Exist in all three states (g, l, s) Elements are colored Fluorine – pale yellow Chlorine – green Bromine – reddish brown Iodine – grayish black solid; violet vapor Typically irritating to skin Forms -1 ions Reactivity decreases down the group

Group 8A: Noble Gases Gases Nonmetals Monoatomic Extremely nonreactive Xenon will react with fluorine to form XeF2, XeF4, and XeF6 Krypton forms KrF2