2/10/16 Today I will determine the shapes of small molecules. Warm Up – Draw the Lewis Structure for CO3-2

Chapter 8 – Molecular Shape Chemistry

Structural Formulas 1. Count up the total number of valence electrons present. 2. Put the element with the lowest electronegativity in the center. 3. Add lone pairs to outside, then inside elements to make an octet. 4. Count up the total number of electrons drawn on! If it equals the total valence number, you are done! 5. If you have used too many electrons, create double or triple bonds, by removing two pairs and creating one more bond….then recount!

Structural Formulas Cl Cl B Cl Exceptions to the Octet Rule! BCl3 Atoms with less than an octet Beryllium is happy with 4 electrons! Boron is happy with 6 electrons! BCl3 You need to recognize that B and Be are fine with less than 8 electrons! Cl B  3 x 1 = 3 v.e. Cl  7 x 3 = 21 v.e. Cl B Cl = 24 v.e.

Structural Formulas F Be F Exceptions to the Octet Rule! BeF2 Atoms with less than an octet Beryllium is happy with 4 electrons! Boron is happy with 6 electrons! BeF2 Be  2 x 1 = 2 v.e. F  7 x 2 = 14 v.e. F Be F = 16 v.e.

Molecular Geometry Structural Formulas explain what atoms are bonded where, but they only show us an atom in two dimensions. Molecular Geometry – shows us an atom in three dimensions!

Molecular Geometry Ball and Stick models – three dimensional physical model of molecular shape.

Molecular Geometry Why do atoms arrange in different shapes? Electrons of the outer atoms want to get as far away from one another as possible. Like charges repel!

Molecular Geometry Valence Shell Electron Pair Repulsion Theory VSEPR Theory In a small molecule, the pairs of valence electrons are arranged as far apart from each other as possible. VSEPR is concerned with both bonded electron pairs (bonds) and unbonded pairs (lone pairs).

Molecular Geometry 1. Draw the structural Formula 2. Determine the Base Geometry by counting the number of substituents 3. Determine the Shape by looking at the number of unbonded pairs *Substituent – an atom or unbonded pair attached to the central atom.

Molecular Geometry – Linear Base Geometry Substi-tuents Lone pairs Base (Electron)Geometry Shape Shape Name Examples Bond Angle 1 0-3 Linear HF, O2 180° 2 BeCl2, CO2 *Any molecule that only has two atoms, must be linear, regardless of unbonded pairs!

Molecular Geometry – Trigonal Planar Base Geometry Substi-tuents Lone pairs Base (Electron) Geometry Shape Shape Name Examples Bond Angle 3 Trigonal Planar BF3, CO3-2 120° 1 Bent NO2-, O3 <120°

Molecular Geometry - Tetrahedral Substi-tuents Lone pairs Base (Electron) Geometry Shape Shape Name Example Bond Angle 4 Tetrahedral CH4, PO4-3 109.5° 1 Trigonal Pyramidal NH3, PCl3 <109.5° 2 Bent - 105 H2O

Homework VSEPR Theory #1 – Find base geometry, and shape for each. Predict bond angles.

2/11/16 Today I will practice VSEPR Warm Up – What is the shape of PBr3?

Expanded Octets Less than octet – He, B, Be More than an octet

Geometry – Trigonal Bipyramidal Substi-tuents Lone pairs Base (Electron) Geometry Shape Shape Name Example Bond Angle 5 Trigonal Bipyramidal PCl5 120°, 90° 1 See Saw SF4 180° 2 T-shaped ClF3 90°, 180° 3 Linear XeF2

Molecular Geometry - Octahedral Substi-tuents Lone pairs Base (Electron) Geometry Shape Shape Name Example Bond Angle 6 Octahedral SF6 90° 1 Square Pyramidal ClF5 <90° 2 Square Planar XeF4

Expanded Octets

2/12/16 Today I will demonstrate molecular shape Warm Up – What is an expanded octet?

2/16/16 Today I will demonstrate molecular shape Warm Up – Describe the method of finding shape.

2/17/16 Today I will demonstrate molecular shape Warm Up – Describe the method of finding shape.

2/18/16 Today I will demonstrate molecular shape Warm Up – What is the base geometry and shape of NCl3

2/19/16 Today I will describe hybridization and bond length. Warm Up – What is the shape of ClO3-1?

Hybrid Orbitals Another theory of molecular geometry is hybridization of orbitals Hybrid Orbitals – combinations of atomic orbitals

Bond Length Different pairs of atoms actually form bonds of different length. Moving down a group, bond length increases Cl---Cl > F---F (larger atoms) Single bonds > Double bonds > Triple bonds C---O > C==O

Drawing Ball & Stick Models

8.1 Review & Reinforcement Don’t do # 16 or 17

2/22/16 Today I will draw molecular polarity Warm Up – What is the base geometry, shape and hybridization of CO2?

Polarity Polarity 1. Bond Polarity 2. Molecule Polarity

Polar Bonds Covalent Bonds can show polarity Polarity – unequal sharing of electrons Partial positive Partial negative F is more electronegative than C, which means it has a greater pull on the electrons in the bond. Therefore, the electrons are unbalanced toward the F.

Electronegativities of Representative Elements Polar Bonds Electronegativities of Representative Elements Fluorine 4.0 Oxygen 3.5 Chlorine 3.0 Nitrogen Bromine 2.8 Carbon 2.5 Sulfur Hydrogen 2.1 Phosphorus Boron 2.0 Silicon 1.8 Significant Electronegativity Difference If the difference is ≤ 0.4, the bond is non-polar. If the difference is > 0.4, the bond is polar Are the following bonds polar or nonpolar? C-C N-O H-P C=O

Polar Molecules Molecules can be polar or non-polar too. Dipole – a molecule with a positive end and a negative end (polar) HF Draw in the dipole arrow. Points toward negative HF only has a polar bond.

Polar Molecules HF was easy to figure out because it was only two atoms. What about CO2? CO2 is composed of two polar bonds, but tests show that it is a nonpolar molecule. HOW?

Polar Molecule In order to determine polarity, you must look at both the bond polarity and the shape of the molecule! Polar molecules will have a NET DIPOLE Where is the center of the positive ends? Where is the center of the negative ends? If there is a separation, draw in a net dipole arrow. CO2 is nonpolar! What shape is CO2? Linear

Polar Molecules H2O Where is the center of the positive ends? Where is the center of the negative ends? If there is a separation, draw in a net dipole (toward negative) H2O is polar! What shape is H2O? Bent - 105

Polar Molecules Typically, if the molecule is symmetrical, it will be non-polar and if the molecule is asymmetrical, it will be polar (as long as the substituents are the same!) Which shapes could be symmetrical?

Polar Molecules H2CO Where is the center of the positive ends? Where is the center of the negative ends? If there is a separation, draw in a net dipole (toward negative) H2CO is polar! What shape? Triangular Planar

Polar Molecules Polarity determined by both shape and the polarity of bonds. Look at H2S

Homework Polar Bonds and Molecules WS

2/23/16 Today I will review polarity Warm Up – Describe how we determine if a molecule is polar or non-polar.

2/24/16 Today I will describe intermolecular forces Warm Up – Draw the ball and stick model of water and show the molecular polarity

Polar Molecules One of the most important molecules on earth is water. Water only has the properties it does because it is polar! Liquid at room temperature Life on Earth might not be possible if water were non-polar!

Intermolecular Forces Intermolecular forces – a force of attraction that exists between neighboring molecules because of their polarity Dipole-dipole Attraction between neighboring dipoles Molecules align in an electrical field

Intermolecular Forces Hydrogen bond – strong dipole bond between the hydrogen atom of a molecule and a highly electronegative atom of another molecule such as F, O or N. Especially useful in water – keeps water a liquid

Large Molecules Small molecules – Shape helps determine polarity Large molecules – Polarity helps determine shape!

Homework 8-2 R & R Don’t do #12 Do #’s 7-11 on the back, or a separate sheet Assume the B-I bond in #13a is non-polar

2/25/16 Today I will review ch 8 Warm Up – Find the following for CS2 base geometry, shape, hybridizations, draw the ball and stick model, bond polarity, molecule polarity (draw in net dipole if there is one)

2/26/16 Today I will review chapter 8 Warm Up – Describe the process of determining whether a molecule is polar or nonpolar from the very beginning.