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Chapter 5 The Periodic Table Objectives • Describe how Mendeleev arranged the elements in his table. • Explain how the predictions Mendeleev made and the discovery of new elements demonstrated the usefulness of his periodic table The Meaning of Periodic • Having or marked by repeated cycles. • Happening or appearing at regular intervals. • Recurring or reappearing from time to time; intermittent. Dmitri Mendeleev 1860’s Only 63 elements were known at that time Mendeleev’s Proposal Mendeleev arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column. Periodic Table An arrangement of elements in columns, based on a set of properties that repeat from row to row. P. 127 Mendeleev’s Periodic Table • Not a complete periodic table • Had to leave spaces in his table • Arrange elements by their mass • Placed element with similar properties in the same column • Was able to predict properties of elements yet to be discovered Gallium Mendeleev’s prediction: Soft metal Low melting point Density of 5.9 g/cm3 Discovery of gallium (1875): Soft metal Melting point = 29.7C Density = 5.91 g/cm3 Objectives • Describe the arrangement of elements in the modern periodic table. • Explain how the atomic mass of an element is determined and how atomic mass units are defined. • Identify general properties of metals, nonmetals, and metalloids. The Modern Periodic Table The elements are arranged by increasing atomic number (number of protons) Period A row in a periodic table of elements Group A column of elements in a periodic table Note: Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups. Periodic Law The pattern of repeating properties displayed by elements in the periodic table Atomic Mass A value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes Atomic Mass Unit (amu) One twelfth (1/12) the mass of a carbon-12 atom Chlorine Isotope Percent found in nature Atomic Mass (AMU) Chlorine-35 75.78% 34.969 Chlorine-37 24.22% 36.966 Classes of Elements 1. Metals 2. Nonmetals 3. Metalloids Metals Elements that are good conductors of heat and electric current Most metals are malleable and ductile Metals (blue) Transition Metals Elements that form a bridge between elements on the left and right sides of the periodic table Transition Metals Nonmetals Elements that are poor conductors of heat and electric current Note: Many nonmetals have a low melting point which causes them to be gases at room temperature. Nonmetals (yellow) Metalloids Elements with properties that fall between those of metals and nonmetals Note: A metalloid’s ability to conduct electric current varies with temperature. Metalloids (pink) Variation Across a Period From right to left, elements become more metallic and less nonmetallic in their properties Variation Across a Period Objectives • Relate the number of valence electrons to groups in the periodic table and to properties of elements in those groups. • Predict the reactivity of some elements based on their locations within a group. • Identify some properties of common A group elements. Valence Electron Note About Valence Electrons Alkali Metals Alkali Metals Alkaline Earth Metals Alkaline Earth Metals Magnesium Calcium: - The Boron Family The Boron Family Metalloid (boron) Metal (aluminum) Metal (gallium) Metal (indium) Metal (thallium) The Boron Family Aluminum - The Carbon Family The Carbon Family Nonmetal (carbon) Metalloid (silicon) Metalloid (germanium) Metal (tin) Metal (lead) The Carbon Family Carbon: - Silicon: - The Nitrogen Family The Nitrogen Family Nonmetal (nitrogen) Nonmetal (phosphorus) Metalloid (arsenic) Metalloid (antimony) Metal (bismuth) The Nitrogen Family Nitrogen & Phosphorus: - The Oxygen Family The Oxygen Family Nonmetal (oxygen) Nonmetal (sulfur) Nonmetal (selenium) Metalloid (tellurium) Metalloid (polonium) The Oxygen Family Oxygen: Sulfur: - Halogens Halogens Nonmetal (fluorine) Nonmetal (sulfur) Nonmetal (bromine) Nonmetal (iodine) Metalloid (astatine) Halogens Halogens Fluorine: Chlorine: - Noble Gases Noble Gases