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apchem_chp3lecture

apchem_chp3lecture - Molecules Ions and their Compounds 2...

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9/20/2011 1 Molecules, Ions and their Compounds 2 Al (s) + 3 Br 2(l) Al 2 Br 6(s) aluminum + bromine aluminum bromide Note: Aluminum reacts with halogens heavier than chlorine to produce “dimers” (in their liquid and gas phases) that are more consistent with the physical and chemical properties of molecules than ionic compounds. Representing Formulas Colors commonly used for representing atoms (Sometimes sulfur is represented by yellow and chlorine by green) The styrene molecule is the building block of polystyrene, a material used for drinking cups and building insulation. What is the molecular formula for styrene? C 8 H 8 Molecular Model Representations: See ACDLabs: Chemsketch at the web site
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9/20/2011 2 Question: Cysteine, whose molecular model and structural formula are illustrated here, is an important amino acid and a constituent of many living things. What is its molecular formula? C 3 NH 7 SO 2 Ionic Compounds: Formulas, Names and Properties Definition: Compounds that are bound together by electrostatic attractions produced by the transfer of electrons between species in the compound. Ionic Compounds -Generally form between metals and nonmetals -The bond between atoms forms from a transfer of electrons from one atom to another. -The one that loses electrons becomes positively charged and is called a “cation”. -The one that gains electrons becomes negatively charged and is called an “anion”. -There is no such thing as an ionic “molecule” because the compound exists as a repeating pattern of positive and negative ions (i.e. an ionic crystal). Cations (positively charged particles) and Anions (negatively charged particles) F = k(n + e)(n - e)/d 2 Given that in the electrostatic force equation the constant k = 8.988x10 9 Nm 2 /C 2 and the ion radii for magnesium and oxygen are 65pm and 140pm, respectively, determine the force between the two atoms in the compound magnesium oxide. (q e = 1.602x10 -19 C) Answer: F = 8.988x10 9 Nm 2 /C 2 (2)(1.602x10 -19 C)(2)(1.602x10 -19 C) / (2.05x10 -10 m) 2 = 2.20x10 -8 N
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9/20/2011 3 Ionic Compound A compound consisting of a positively charged component (cation) and a negatively charged component (anion) Any charged particle is known generically as an “ion”. Ions form from the transfer of one or more electrons from one species to another The charged particles are electrostatically attracted to one another forming a crystalline structure with a repeating pattern of positive and negative particles. Sn 4+ Pb 4+ Ni 3+ Usually fixed charge in ionic compounds Many transition and post-transition metals have more than one possible charge. Empirical Formula - Provides information about the (quantity) ratio of combined elements in a compound written in lowest terms. Ex. Rb 2 O (Two rubidium atoms combine with one oxygen atom) -When writing the formula for an ionic compound, the cation is always listed first.
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