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The Periodic Table Objective • You will be able to discuss the contributions of Mendeleev, Moseley, and Seaborg in the development of the periodic table. The Periodic Table Dmitri Mendeleev (1869): published first periodic table. Mendeleev’s Periodic Table • arranged by increasing atomic mass • grouped by similar properties • predicted the existence and properties of unknown elements (Ga, Ge, Hf) Mendeleev’s Predictions Property Prediction for ekasilicon Actual for Ge Atomic mass 72 amu 72.59 amu Density 5.5 g/cm3 5.32 g/cm3 Formula of oxide EsO2 GeO2 Formula of chloride EsCl4 GeCl4 Predicted in 1871; Ge was discovered in 1886. Mendeleev’s Question Is the atomic mass of Tellurium (Te) incorrect? Henry Moseley Henry Moseley (1911): each element has different # of p+. The table should be arranged by atomic number, not atomic mass. Moseley was killed in Turkey during WWI. The Modern Table Glenn Seaborg arranged our modern table (d-block and f-block). Objectives • Know the periodic law. • Explain how atomic radius is measured. • Understand, identify, and discuss the trends on the periodic table for atomic radius and for electronegativity. Periodic Law periodic law: the properties of the elements repeat periodically “periodicity” Atomic Radius It is difficult to measure atomic size (no definite edge). atomic radius: ½ the distance between the nuclei of two bonded atoms Atomic Radius Trends group trend (down a column): radius increases because new energy levels period trend (across a row): radius decreases because electrons are in the same “shell” but added protons pull inward on the shell. Electronegativity electronegativity: the tendency of an atom to attract electrons when it is bonded to another atom The nucleus of a small atom pulls strongly on the outer electrons of a large atom + + + Electronegativity Trends group trend: electronegativity decreases (atoms get larger) period trend: electronegativity increases (atoms get smaller) Objectives • You will be able to compare the reactivity of elements. • You will be able to explain why specific elements are either reactive or unreactive. Metals and Non-Metals Metals tend to lose their outer “valence” electrons because they are large (low electronegativity). Non-metals tend to attract electrons because they are small (high electronegativity). Reactivity Trends same group = similar properties (like reactivity) = similar e- configurations metals: largest, with fewest valence e- are most reactive non-metals: smallest, with most valence e- are most reactive (excluding noble gases—outer shell is full) Which is the most reactive? • Ca, Cu, Rb, Na • S, Cl, Br, C, Ne Reaction Clips • Alkali Metal Reactions • Sodium and Chlorine Reaction • Fluorine Reactions