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Chapter 7 Periodic Properties of Elements Burns FUNDAMENTALS OF CHEMISTRY 4/e The Periodic Table of Elements • Elements are organized according to their physical and chemical properties in the Periodic Table of the Elements. Mendeleev • Father of the Periodic Table (1869) • Mendeleev’ Mendeleev’s Periodic Law- Both physical and chemical properties of the elements vary periodically with increasing atomic mass. (Å slightly flawed) • Modern Periodic Law: Both physical and chemical properties of the elements vary periodically with increasing atomic number (Required!) 1 Periodic Table of the Elements Lanthanides (rare earth) Actinides From Chapter 4 Periods of Elements • Periods of elements are the horizontal rows of the Periodic Table. • The properties of the elements vary as you move from left to right across the periods. – Periodicity Groups (a.k.a. Families) • Vertical columns of elements in the periodic table are called groups. • Elements in the same group or family have similar chemical properties. • Main Group (Representative) Elements are those in the first two groups and the last six groups in the periodic table. These groups are designated IA - VIIIA group elements 2 Valence Electrons (Section 5.4, p. 130) • Number of valence electrons = group number (Roman) • The number of valence electrons increases as you move from left to right across a period. • The periodic changes in properties (periodicity) parallels the change in the number of valence electrons. Periodic Trends • Atomic Radius (required!) – Left Æ right within the period: decrease (why?) – Top Æ bottom within the group: increase (why?) • Ionic radius (required!) – Atom Æ anion: increase; atomÆ cation: decrease – Isoelectronic (?) ions/atom: higher Z, smaller radius • Ionization Energy (required!) – Left Æ right within the period: increase – Top Æ bottom within the group: decrease – Trends opposite that of atomic radius (why?) • Melting points and boiling points (self study) • Density and conductivity (self study) Survey of Elements by Groups Sec. 7.7 3 Group IA, The Alkali Metals • Elements are: – Low ionization potential – Highly reactive with water, oxygen, other elements – Na is 6th in abundance. K is 7th in abundance in earth’s crust. Group IIA, Alkaline Earth Metals • The elements: – – – – Low IE (but higher than group IA). Are less reactive than group IA. Have 2 valence electrons and form 2+ ions. Calcium is fifth in abundance in the earth’s crust Group IIIA • Boron is a metalloid; Others are metals • Metallic elements form +3 ions. Organic Boron Chemistry: Herbert C. Brown (1912-2004) Nobel Chemistry Laureate, 1979 4 Group IVA, The Carbon Family • Metallic character increases with increasing Z. • Carbon has several allotropes (forms) • Carbon ≡ Energy – Carbohydrates – Hydrocarbons (petroleum) – CO2 – greenhouse gas • Silicon: second most abundant (earth’s crust); Exist as SiO2 (silica) and silicates Allotropes of Carbon Å C60 a.k.a. Bucky Ball Allotropes: Forms of an element having different physical properties due to different atomic arrangements Group VA • N2, 78% of air • Nitrogen in amino acids & nucleic acids. • N2 & H2 to form ammonia, NH3 • P - Allotropes: red; yellow-white • Phosphate (PO43-) esters – DNA/RNA linkers 5 Group VIA, The Oxygen Family (Chalcogens) Chalcogens) • Oxygen as O2 gas is essential to life. – O2 is the oxidizer in combustion and metabolism – O2 is 21% of the earth’s atmosphere • Oxygen makes up 49% of the earth’s crust. • Ozone, O3, is an allotropic form of oxygen. • Sulfur occurs free in nature as S8 • S used in sulfuric acid (H2SO4) and in making tires (vulcanization) Group VIIA, The Halogens • Halogens contain 7 valence electrons, exist as diatomic gas. • Fluorine is a reactive, pale, yellow gas. • Chlorine is a reactive green - yellow gas • Bromine is a red liquid (highly corrosive) • Iodine is a purple crystalline solid that sublimes Group VIIIA, Noble Gases • Mono- atomic gases; 8 valence electrons 6