Molecular Models Activity carbon tetrachloride methane water ethane ethyne dihydrogen monosulfide carbon dioxide ammonia hydrogen monochloride trichloromethane urea propane butane nitrogen triiodide (video) supplies

Bonding and Shape of Molecules Number of Bonds Number of Unshared Pairs Covalent Structure Shape Examples 2 3 4 1 2 -Be- Linear Trigonal planar Tetrahedral Pyramidal Bent BeCl2 BF3 CH4, SiCl4 NH3, PCl3 H2O, H2S, SCl2 B C N : O :

Lewis Structures 1) Count up total number of valence electrons 2) Connect all atoms with single bonds - “multiple” atoms usually on outside - “single” atoms usually in center; C always in center, H always on outside. 3) Complete octets on exterior atoms (not H, though) - no unpaired electrons (free radicals) 4) Check - valence electrons match with Step 1 - all atoms (except H) have an octet; if not, try multiple bonds - any extra electrons? Put on central atom

Carbon tetrachloride Cl Cl C Cl Cl Cl C CCl4 Tetrahedral geometry Carbon tetrachloride – “carbon tet” had been used as dry cleaning solvent because of its extreme non-polarity.

Methane H H C H H H C Tetrahedral geometry Methane –The first member of the paraffin (alkane) hydrocarbons series. a.k.a. (marsh gas, CH4).

Water d(-) .. .. SO2 Bent geometry H O d(+) Polar molecule

Ethane H H H C C H H H C2H4 C = 1s22s22p2 ball-and-stick Lewis dot notation C2H4 molecular formula space-filling molecule

Ethane H H H C C H H H C2H6 ball-and-stick Lewis dot notation molecular formula space-filling molecule

Ethyne H C C H C H C H H C C H C2H2 No octet 6 electrons = triple bond each C “feels” 6 electrons H C C H C H C H Stable octet C2H2 H C C H each C “feels” 7 carbons Ethyne – a.k.a. “acetylene”

Dihydrogen monosulfide .. .. SO2 H S Bent

Carbon dioxide O C O O C O O C Linear geometry CO2

Ammonia N 107o H .. .. N H N H N H H NH3 H Trigonal Pyramidal geometry

: : : : Amino Acids – Functional Groups NH21- R- COOH NH21- NH3 NH41+ Amine Base Pair Carboxylic Acid NH21- R- COOH lose H+ H+ NH21- NH3 NH41+ : N H : 1+ : 1- N N : H H H H H amine ammonia ammonium ion

Hydrogen monochloride Cl H H Cl Cl HCl d(+) d(-) HCl(g) + H2O(l)  HCl(aq) hydrogen chloride water hydrochloric acid Polar molecule

Trichloromethane H H Cl C Cl Cl C Cl Cl Cl H C Cl d(+) CHCl3 d(-) Tetrahedral geometry Polar molecule

Urea H H H H N N O C O C N N H H H H CO(NH2)2 NOT “di-urea” Urea – The first organic compound to be synthesized (Wohler, 1828).

Propane H H H H H H C C C H C C C H H H H H H H H H C3H8

Butane H H H H H C C C C H H H H H H H H H H - C - C - C - C - H

Nitrogen triiodide N I I I .. N I NI3 Trigonal Pyramidal geometry Video clip: (slow motion) detonation of NI3

Supplies 15 black (carbon) 8 green (chlorine and iodine) 1 yellow (sulfur) 4 blue (oxygen) 4 red (nitrogen) 42 hydrogen (hydrogen) 67 bonds (bonds)

C Cl I S N O H Cl H Cl C Cl H C H O C O Cl H S H H C C H H H Cl C Cl CHCl3 HCl

H H H H H H H H C C C C H H C C C H H H H H H H H N N I I H H H I

Decomposition of Nitrogen Triiodide

Decomposition of Nitrogen Triiodide Molecules store energy (chemical potential energy) in the bonds that hold them together. When the bonds are broken, energy is released. 2 NI3(s) N2(g) + 3 I2(g)

N H .. .. C H O .. H H .. O CH4, methane NH3, ammonia H2O, water O lone pair electrons O O O3, ozone

The VSEPR Model .. .. .. The Shapes of Some Simple ABn Molecules O S O Linear Bent Trigonal planar Trigonal pyramidal AB6 F P F S F Cl Students often confuse electron-domain geometry with molecular geometry. You must stress that the molecular geometry is a consequence of the electron domain geometry. The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them. F Xe T-shaped Square planar Trigonal bipyramidal Octahedral Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 305