1 Geometry of Molecules DO NOW: Draw the Lewis Dot Diagram for: MgOH 2 OCO 2 HW: In Peason Chemistry textbook, read pages and then complete # 22, 26, & 28 on page 246

2 Geometry of Molecules HW: In Peason Chemistry textbook, read pages and then complete # 22, 26, & 28 on page 246 Butane

3 Geometry of Molecules Although structural formulas are very useful tools, they are not very realistic representations of molecules. Butane

4 Geometry of Molecules Structural formulas make all molecules look flat, when they actually occupy three-dimensional space. Butane

5 Geometry of Molecules Ball and stick models, which you will work with in the lab, make it easier to visualize the shapes of molecules.

6 Geometry of Molecules Now that we know several ways to represent molecules, we might wonder what gives various molecules their distinctive shapes?

7 Geometry of Molecules Both water and carbon dioxide have three atoms per molecule, yet one is linear (straight) and the other is bent. How can we account for this difference?

8 Geometry of Molecules Chemists use the valence-shell electron-pair repulsion model (VSEPR) to explain differences in shapes.

9 Geometry of Molecules The most important concept to understand in the valence-shell electron-pair repulsion model is that the electrons all have negative charges, and like charges repel each other. The individual molecule will take on a shape that allows these electrons to be as far away from each other as possible.

10 Geometry of Molecules It is also important to note that the valence electrons that are not involved in bonding take a greater three-dimensional space than a pair of bonding electrons.

11 Geometry of Molecules So it is actually the nonbonding electrons in the valence shell of a oxygen atom that gives water a bent shape. Nonbonding electrons

12 Geometry of Molecules Carbon dioxide has oxygen atoms with nonbonding electrons too, but the symmetrical distribution results in a linear shape. Nonbonding electrons

Lewis Dot for Compounds RULES: Rule #1 Count the total number of VALENCE ELECTRONS in the molecule or ion.

Rule #2 If the particle is an ION, add 1 electron for each negative charge, and subtract an electron for each positive charge.

Rule #3 Try to create a symmetrical structure with the atoms and bonds. CARBON BONDS TO CARBON LEAST ELECTRONEGATIVE ATOM IN THE MIDDLE.

Rule #4 Then add unshared electrons to complete the OCTET RULE of each atom in the compound.

Rule #5 The number of electrons in the final skeleton must agree with the number of electrons calculated in Rule #1. IF NOT, THEN DOUBLE AND TRIPLE BONDS MUST BE ADDED IN THE APPROPRIATE SECTIONS TO MAKE THE TWO NUMBERS AGREE.

Molecular Shape and the VSEPR Model PREMISES: a)Shared and unshared electrons repel each other

b) An unshared pair of electrons repel more strongly than a shared pair of electrons. c) Single, Double and Triple bonds are considered equivalent when determining spacing of atoms.

d) The particular shape of the molecule or ion is determined by the electrons being placed as far from each other as possible.

# of PAIRED ELECTRONS (AROUND THE CENTRAL ATOM) FORMULASHAPE 2AB 2 LINEAR 3AB 3 TRIGONAL PLANAR 4AB 4 TETRAHEDRAL

SHARED PAIRS (AROUND THE CENTRAL ATOM) UNSHARED PAIRS (AROUND THE CENTRAL ATOM) FORMULASHAPE 21AB 2 BENT 22AB 2 BENT 31AB 3 TRIGONAL PYRAMIDAL

BOND POLARITY ELECTRONEGATIVITY- The ability of an atom to attract electrons to itself.

RANGEBOND TYPEEXAMPLE 0 – 0.4Non-polar covalent BrCl 0.41 – 1.69Polar covalentHBr 1.70 – 3.3IonicNaCl

POLARITY IN MOLECULES Polar Molecule – A molecule that contains a polar covalent bond(s) with an asymmetrical charge distribution.

Non-Polar Molecule – A molecule that contains… a)only non-polar covalent bonds b) polar covalent bonds in a molecule with a symmetrical charge distribution.

27 Geometry of Molecules

28 Geometry of Molecules

29 Geometry of Molecules Example 1. What is the shape of a sulfur dioxide (SO 2 ) molecule?

30 Geometry of Molecules Example 2. What is the shape of a sulfur trioxide (SO 3 ) molecule?

31 Geometry of Molecules Example 3. What is the shape of a nitrogen (III) fluoride (NF 3 ) molecule?

32 Geometry of Molecules Example 5. What is the shape of the molecule represented by the ball and stick model below?

33 Geometry of Molecules Example 6. What is the shape of the molecule represented by the ball and stick model below?

34 Geometry of Molecules Example 7. What is the shape of the molecule represented by the ball and stick model below?

35 Geometry of Molecules

36 Geometry of Molecules Video for visual representation, if baseline expectations have been met. Video for visual representation, if baseline expectations have been met CLASSWORK: In the Prentice Hall workbook (blue & red) complete section 8.3, pg HW: In Peason Chemistry textbook, read pages and then complete # 22, 26, & 28 on page 246