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Chapter 11 The Periodic Table I. History of the Periodic Table • Johann Wolfgang Döbereiner and triads • John Newlands and the Law of Octaves • Dmitri Mendeleev and the 1st periodic table Mendeleev’s Periodic Table Mendeleev’s Predictions Predicted properties for Mendeleev’s Eka-Silicon and properties of Germanium: Element Eka-Silicon (predicted 1871) Germanium (discovered 1886) Atomic Weight Density Oxide formula Chloride formula 72 5.5 g/cm3 EsO2 EsCl4 72.59 5.32 g/cm3 GeO2 GeCl4 Periodic Law • Basis: Element arranged according to their atomic masses present a clear periodicity of properties • Modern: The properties of elements repeat periodically when the elements are arranged in increasing order by their atomic numbers Circular Periodic Table Benfey’s Periodic Table Physics Periodic Table ADOMAH periodic table - electron orbitals Spiral Periodic Table We like spirals! Periodic system Pyramid format Periodic system: Zmaczynski & Bayley Periodic table in binary electron shells layout, designed by Eric William McPherson Regions of the Periodic table Representative Elements -EC • Valence v. core electrons Representative Elements - Ions • Generalization of atom/ion stability – Usually means 8 valence = octet rule Transition Elements - EC • Remember the exceptions to filling d orbitals Periodic Trends – Atomic Radii • Worksheet: Atomic Size • Why does atomic radius decrease across a period? – Higher # = more protons = higher core charge • Increased attraction between p+ & eSmaller radius – e- pulled closer to nucleus = ???? • Why does atomic radius increase down a group? – Valence electron shell higher n = higher probability Larger radius of finding e- further from nucleus = ???? – Shielding by core e- = less pull on valence e- = ???? Larger radius Atomic Radii Periodic Trends – Ionic Radii • Cation (+) radii are smaller than atomic radii – Why? • Lose of valence e• Results in lower n, resulting in stronger nuclear pull • Anion (-) radii are larger than atomic radii – Why? • Gain of e• Results in increased repulsion between e- Sizes of Anions (- ions) Sizes of Cations (+ ions) Graph of Atomic Radii Definition of Ionization Energy (IE) • Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first or initial ionization energy or Ei of an atom or molecule is the energy required to remove one mole of electrons from one mole of isolated gaseous atoms or ions. You may think of ionization energy as a measure of the difficulty of removing electron or the strength by which an electron is bound. The higher the ionization energy, the more difficult it is to remove an electron. Therefore, ionization energy is an indicator of reactivity. Periodic trends – 1st Ionization Energy exceptions Periodic Trends – 2nd Ionization Energy 1 2 3 4 5 6 7 8 H 1312 He 2372 5250 Li 520 7297 11810 Be 899 1757 14845 21000 B 800 2426 3659 25020 32820 C 1086 2352 4619 6221 37820 47260 N 1402 2855 4576 7473 9442 53250 64340 O 1314 3388 5296 7467 10987 13320 71320 84070 F 1680 3375 6045 8408 11020 15160 17860 92010 Ne 2080 3963 6130 9361 12180 15240 Na 496 4563 6913 9541 13350 16600 20113 25666 Mg 737 1450 7731 10545 13627 17995 21700 25662 *The teal colored cells represent ionization energies where the valence shell is now (n-1). (Why do you think there is such a large jump in the ionization energies when the n-1 shell is now valence?) Periodic Trends - Electronegativity • Definition • Increases across a period (L to R), decreases down a group (top to bottom) Electronegativity • Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. • The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to Cesium and Francium which are the least electronegative at 0.7. Electron Affinity! Electron Affinity Definition • the quantitative measure, usually given in electron-volts (eV), of the tendency of an atom or molecule to capture an electron and to form a negative ion. Periodic Trend for electron affinity Periodic Trends - All *Note: The electron affinity of an element is the energy given off when a neutral atom in the gas phase gains an extra electron to form a negatively charged ion Wrap-up • Periodic Table Activity