Chemistry 2 week one notes
Chemistry 2 week one notes chem 132
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This 11 page Class Notes was uploaded by Ariel Kamen on Thursday February 4, 2016. The Class Notes belongs to chem 132 at Towson University taught by Sarah T. Stokes in Winter 2016. Since its upload, it has received 55 views. For similar materials see general chemistry lecture 2 in Chemistry at Towson University.
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Date Created: 02/04/16
1/28/16 Chemistry 2 Notes • Lewis dot structure and VSEPR review formula —> L.D.S —> geometry VSEPR —> polarity —> IMFs —> properties Intermolecular Forces: between 2+ molecules Surface tension Viscosity Volatility M.P. B.P. Vapor Pressure Solability properties (bulk) Intramolecular Forces: within a molecule (*covalent & ionic bonds) 1. Count valence electrons (e) 2. Least electronegative goes into the center (NOT….. H & F) 3. Make single bonds 4. Place remaining e around outer atom 5. Make double or triple bonds if necessary 6. Check! Octets, number of e, resonance, etc. Lewis Dot Structure Exceptions to octet rule: Incomplete octet: H, B, Li, Be, Al Expanded octet: row 3 and below! P, S, Cl, Br, I, As, Se….. 2/2/16 What Determines the Shape of a Molecule? • simply put electron pairs, whether they be bonding or nonbonding, repel each other • by assuming the electron pairs are placed as far as possible from each other, we can predict the shape of the molecule Electron Domains • we can refer to the electron pairs as electron domains • in a double or triple bond, all electrons shared between those 2 atoms e domains electron geometry molecular geometry 2 linear —————> linear 3 trigonal planar ———————> trigonal planar (3 b.p.) bent (2 b.p., 1 l.p.) 4 tetrahedral —————————> tetrahedral (4 b.p.) trigonal pyramidal (3 b.p., 1 l.p.) bent (2 b.p., 2 l.p.) 5 trigonal bipyramidal —————> trigonal bipyramidal (5 b.p.) seesaw (4 b.p., 1 l.p.) Tshaped (3 b.p., 2 l.p.) linear (2 b.p., 1 l.p.) 6 octahedral ————————> octahedral (6 b.p.) square pyramidal (5 b.p., 1 l.p.) square planar (4 b.p., 2 l.p.) ElectronDomain Geometries central atomhe electrondomain geometries for two through six electron domains around a Molecular Geometries • the electrondomain geometry is often NOT the shape of the molecule, however • the molecular geometry is that defined by the positions of only the atoms in the molecules, not the nonbonding pairs Linear Electron Domain • In this domain, there is only one molecular geometry: linear. • NOTE: If there are only two atoms in the molecule, the molecule will be linear no matter what the electron domain is. Trigonal Planar • there are 2 molecular geometries trigonal planar, if all the electron domain bent, if one of the domains is a nonbonding pair Tetrahedral • there are 3 molecular geometries tetrahedral, if all are bonding pairs trigonal pyramidal if one is a nonbonding pairs bent if there are two nonbonding pairs Trigonal Bipyramidal • there are 2 distinct positions in this geometry axial ( north and south pole) equatorial (equator) —> this is where lone pairs will be • lowerenergy conformations result from having nonbonding electron pairs in equatorial, rather than axial, positions in this geometry • there are four distinct molecular geometries in this domain: – Trigonal bipyramidal – Seesaw – Tshaped – Linear Octahedral • all positions are equivalent in the octahedral domain. • there are three molecular geometries: – Octahedral – Square pyramidal – Square planar Practice: Polar Covalent Bonds: • although atoms often from compounds by sharing electrons, the electrons are not always shared equally • Flourine pulls harder on the electrons it shares with hydrogen than hydrogen does • therefore, the Flourine end of the molecule has more electron density than the hydrogen end Polarity • but just because a molecule possesses polar bonds does not mean that molecule as a whole will be polar • CO2 is nonpolar because the ‘ends’ balance each other out • water is polar because oxygen pulls electrons to itself and because the shape of the molecule puts this electron rich area (red) at one ‘end’ of the molecule (unbalanced) IM s intra —> within molecule (covalent bonds) inter—> between molecules (10x less strong than covalent bonds) Pure Substances weakest 1. Dispersion london dispersion forces (LDF) or van der woods forces *found in all molecules • temporary dipole temp. force that happens when electrons in 2 adjacent atoms occupy positions • bigger atoms/more atoms —> more e; more dispersed • polarizability how will can an atom or molecule change itself to “look” polar 2. Dipoledipole (dd) 2/4/16 **SKIP 12.4 12.5 Four types of crystals: ALL SOLIDS Ionic ionic bonding, brittle, hard high melting point does not conduct heat or electricity Molecular covalent bonds, within a molecule, IMF’s between molecules low m.p. and b.p. soft does not conduct heat/electricity Covalent all covalent bonds hard high m.p. does not conduct heat/electricity Metallic metallic bonds soft to hard low to high conduct heat/electricity
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