Index UIL Chemistry Info Part 2 Honors Unit 041

Index Lewis Dot Structures Molecular Geometry (VSEPR) Molecular Geometry (VSEPR) Polar Vs Nonpolar Molecules Polar Vs Nonpolar Molecules Honors Unit 042

Index Lewis Structures Honors Unit 043

Index Electron dot notation used to represent molecules Helps determine how atoms are connected to each other. Allows us to draw the structural formula of molecules. Shared electrons Lone pairs (unshared electrons) 1 pair shared = single bond Lewis Structure of a Molecule

Index Common atoms Carbon – 4 covalent bonds Nitrogen, phosphorus – 3 covalent bonds Oxygen, sulfur – 2 covalent bonds Hydrogen – 1 covalent bond.

Index 1.Determine the number of valence electrons for each atom in the molecule. 2.Add all the valence electrons together. 3.Arrange the atoms to form a skeleton of the molecule. C is always a central atom If no C, then the least electonegative element is central. H is never central since it can only form one bond. 4.Place a single pair of electrons between each atom. 5.Add lone pairs to each atom until each has a full outer shell (usually 8) (hydrogen 2) 6.Count valence electrons. (must equal step 2) 7.If not equal, start over but add double or triple bond. (every 2e - over add another bond) Drawing the Lewis Structure of a Molecule

Index Drawing Lewis Structures Examples Methanol, aka methyl alcohol, MeOH: CH 3 OH C4e - 1 x 4e - = 4e - H1e - 4 x 1e - = 4e - O6e - 1 x 6e - = 6e = 14e -

Index Drawing Lewis Structures Examples Methanol, aka methyl alcohol, MeOH: CH 3 OH C4e - 1 x 4e - = 4e - H1e - 4 x 1e - = 4e - O6e - 1 x 6e - = 6e = 14e - Draw skeleton

Index Drawing Lewis Structures Examples Methanol, aka methyl alcohol, MeOH: CH 3 OH C4e - 1 x 4e - = 4e - H1e - 4 x 1e - = 4e - O6e - 1 x 6e - = 6e = 14e - Draw skeleton. Pair of electrons between each pair of atoms.

Index Drawing Lewis Structures Examples Methanol, aka methyl alcohol, MeOH: CH 3 OH C4e - 1 x 4e - = 4e - H1e - 4 x 1e - = 4e - O6e - 1 x 6e - = 6e = 14e - Draw skeleton. Pair of electrons between each pair of atoms. Fill outer shell around each atom.

Index Drawing Lewis Structures Examples Methanol, aka methyl alcohol, MeOH: CH 3 OH C4e - 1 x 4e - = 4e - H1e - 4 x 1e - = 4e - O6e - 1 x 6e - = 6e = 14e - Draw skeleton. Pair of electrons between each pair of atoms. Fill outer shell around each atom. Count valence electrons – 14 Numbers match – done.

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e -

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e -

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e -

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e -

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e - 14e - 2e - too many.

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e - 14e - 2e - too many. Start over with a double bond.

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e - 14e - 2e - too many. Start over with a double bond.

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e -

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e - 12 e - Done

Index Drawing Lewis Structures Examples Ethene: CH 2 CH 2 C 4e - 2 x 4e - = 8e - H 1e - 4 x 1e - = 4e = 12e -

Index Lewis Structures Examples Carbon dioxide Water Carbon monoxide Ammonia Carbon tetrachloride dichloromethane Butane, C Butene N-propanol

Index Molecular Geom Honors Unit 0423

Index MOLECULAR GEOMETRY The shape of molecules. Honors Unit 0424

Index VSEPR Theory Valence Shell Electron Pair Repulsion For covalent compounds.

Index VSEPR Theory Electron pairs repel each other. This includes Bonding pairs and Lone pairs of electrons. This causes the electron pairs to be oriented as far away from each other as possible.

Index Important Notice In the VSEPR theory, double and triple bonds are counted as a single bonding pair even though double bonds have two pairs of electrons and triple bonds have three pairs of electrons.

Index Molecular Shapes The shape of a molecule is determine by how many bonding electron pairs surround the central atom. The number of bonding and lone pairs around the central atom tells you the electronic geometry of the molecule. From which the molecular geometry can be determined.

Index

Geometry of Molecules Electronic geometry: the geometric shape made by all the pairs of electrons. (VSEPR: pairs spread out due to repulsion of like charges.) Molecular geometry: the shape made by the actual atoms (bonding pairs) in the molecule.

Index Example: Carbon dioxide (CO 2 ) 2 Pairs Total 2 Bonding pair 0 Lone pairs Linear molecule

Index Example: Carbon monoxide (CO ) 2 Pairs Total 1 Bonding pair 1 Lone pair Linear molecule

Index 3 Pairs Total 3 bonding pairs 0 lone pairs Trigonal planar molecule

Index 3 Pairs Total 2 Bonding Pairs 1 Lone pair Bent molecule.

Index 4 Pairs Total: 4 bonding pairs 0 Lone Pairs Tetrahedral molecule

Index 4 Pairs Total 3 bonding pairs 1 Lone pair Trigonal pyrimidal

Index 4 Pairs Total 2 Bonding Pair 2 Lone Pair Bent molecule

Index

Molecular Geometry Procedure 1.Draw the correct Lewis structure for the molecule. 2.Count the total number of pairs of electrons around the central atom. (Remember: double & triple bonds count as 1 pair of electrons.) 3.Determine the electronic geometry from the total number of pairs of electrons. 4.Count the number of bonding pairs of electrons. 5.Determine the molecular geometry from the electronic geometry and number of bonding pairs of electrons.

Index Molecules with only two atoms can form only one molecular geometry. What is it?

Index Molecular Geometry GP Determine the molecular geometry of the following compounds: Hydrogen sulfide, (H 2 S)

Index Molecular Geometry GP Determine the molecular geometry of the following compounds: Formaldehyde (H 2 CO)

Index Molecular Geometry GP Determine the molecular geometry of the following compounds: Ammonia (NH 3 )

Index Molecular Geometry GP Determine the molecular geometry of the following compounds: Phosphorous trichloride (PCl 3 )

Index Polar vs Nonpolar Honors Unit 0445

Index Dipoles 1.Created when equal but opposite charges are separated by a short distance. 2.Occur with ionic & polar covalent bonds. 3.Direction of dipole is from positive to negative

Index Polar vs Nonpolar molecules 1.A compound is polar if the dipoles do not cancel each other out.

Index Polar vs Nonpolar molecules 1.A compound is polar if the dipoles do not cancel each other out. Polar

Index Polar vs Nonpolar molecules 1.A compound is polar if the dipoles do not cancel each other out. 2.A compound is nonpolar if the dipoles cancel or there are no dipoles.

Index Polar vs Nonpolar molecules 1.A compound is polar if the dipoles do not cancel each other out. 2.A compound is nonpolar if the dipoles cancel or there are no dipoles. Dipoles cancel. Nonpolar

Index Polar vs Nonpolar molecules 1.A compound is polar if the dipoles do not cancel each other out. 2.A compound is nonpolar if the dipoles cancel or there are no dipoles. Dipoles cancel: nonpolar

Index Polar vs Nonpolar molecules 1.A compound is polar if the dipoles do not cancel each other out. 2.A compound is nonpolar if the dipoles cancel or there are no dipoles.

Index Polar vs Nonpolar molecules 1.A compound is polar if the dipoles do not cancel each other out. 2.A compound is nonpolar if the dipoles cancel or there are no dipoles. 3.Like dissolves like: Polar solvents dissolve polar compounds Nonpolar solvents dissolve nonpolar compounds Oil and water do not mix because water is polar and oil is nonpolar.

Index Polar Vs Nonpolar: Lewis Structure The simple way to tell if a molecule is polar or nonpolar is to look at the central atom in the Lewis structure: A nonpolar molecule will have the same thing all the way around (all the same atom). A polar molecule will have at least one thing different (different atoms or lone pairs around the central atom). This method does not work every time.

Index Polar Vs Nonpolar: Lewis Structure Examples:

Index Properties of Water 1.Universal Solvent: Dissolves polar covalent substances and ionic substances 2.Adhesion, cohesion, and high surface tension 3.High melting point, high boiling point (compared to nonpolar molecules of the same size) 4.Water resist temperature changes. High specific heat, high heat of vaporization 5.Water expands when it freezes (floats)

Index Surface Tension Caused by cohesion The surface layer of polar molecules are more tightly hydrogen bonded to each other because they are not surrounded on all sides by molecules.

Index Surface Tension Examples - No Notes Walking on water Small insects such as the water strider can walk on water because their weight is not enough to penetrate the surface.

Index Surface Tension Examples - No Notes Floating a needle If carefully placed on the surface, a small needle can be made to float on the surface of water even though it is several times as dense as water. If the surface is agitated to break up the surface tension, then needle will quickly sink.

Index Surface Tension Examples - No Notes Floating a needle If carefully placed on the surface, a small needle can be made to float on the surface of water even though it is several times as dense as water. If the surface is agitated to break up the surface tension, then needle will quickly sink. Soaps and detergents help the cleaning of clothes by lowering the surface tension of the water so that it more readily soaks into pores and soiled areas.

Index Surface Tension Examples - No Notes Washing with cold water The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent. But if the detergent lowers the surface tension, the heating may be unneccessary. Drops

Index Capillary Action - No notes