Valence Shell Electron Pair Repulsion Theory Planar triangular Valence Shell Electron Pair Repulsion Theory Tetrahedral Trigonal bipyramidal Octahedral

VSEPR Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

Molecular Structure Molecular structure – the three-dimensional arrangement of atoms in a molecule

VSEPR Theory VSEPR Theory (Valence Shell Electron Pair Repulsion Theory) A model for describing the shapes of molecules whose main postulate is that the structure around a given atom is determined by minimizing the electron pair repulsion Therefore, the electrons and elements bonded to the central atom want to be as far apart as possible

VSEPR Theory Based on Lewis structures we can know the shape or “geometry” of molecules The theory that predicts geometry (based on Lewis structures) is abbreviated VSEPR VSEPR (pronounced “vesper”) stands for Valence Shell Electron Pair Repulsion VSEPR, as the name suggests, predicts geometry based on the repulsion of electron pairs (in bonds or by themselves) Electrons around the central nucleus repel each other. Thus, resulting structures have atoms maximally spread out (balloon demo)

VSEPR overview The balloons represent electron clouds. At the end of each balloon will be a peripheral atom. The balloons meet at a central atom. Each shape containing 2-6 peripheral atoms has a name (you will have to know these) Sometimes the molecules are represented by AXY, where Y is the # of peripheral atoms AX2 = linear AX3 = planar triangular AX4 = tetrahedral (tetra = 4 faces) AX5 = trigonal bipyramidal (2 pyramids) AX6 = octahedral (octa = 8 faces) Work on handout (follow instructions on sheet)

VSEPR Steps Draw the Lewis structure for the molecule Count the total number of things that are around the central atom to determine the electron pair geometry Imagine that the lone pairs of electrons are invisible and describe the molecular shape

SORRY… Yes…you must memorize the main shapes and bond angles

2 Electron Pairs If there are 2 things attached to the central atom, the shape is linear Bond angle = 180°

VSEPR: Two Electron Pair Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

3 Electron Pairs If there are 3 electron pairs the shape will be trigonal planar Bond angle = 120°

VSEPR: Lone Pairs

Lone pairs Thus far we have considered (built) only structures where there are no free electrons around the central atom H C H C Vs. H N H N or or These electrons that are not involved in bonds are called “lone pairs” Essentially, they have the same influence on molecular structure as electron pairs in bonds The result is some weird shapes and names…

3 electron pairs Now imagine that you have 3 electron pairs, but one is just a lone pair (invisible) what would it look like then?

VSEPR: Three Electron Pair Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

4 electron pairs If there are 4 electron pairs, the shape will be tetrahedral Bond angle = 109.5°

Variations on Tetrahedral Molecule The tetrahedral molecule is AX4 Lone pairs can be indicated with AXYEZ, where Z is the number of lone pairs By replacing 1 bond with a lone pair the tetrahedral shape becomes “trigonal pyramidal” AX3E By replacing two bonds with lone pairs we get a “bent” (non-linear) shape (AX2E2 )

4 electron pairs What if 1 of the electron pairs is a lone pair (invisible)? What would it look like then? Trigonal Pyramidal

4 electron pairs What if there are 2 lone pairs (invisible)? What would it look like then? bent

VSEPR: Four Electron Pair Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

5 electron pairs If there are 5 electron pairs the shape will be Trigonal Bipyramidal Bond angles = 90º & 120º

Variations on Trigonal Bipyramidal AX5 is trigonal bipyramidal AX4E is unsymmetrical tetrahedron AX2E3 is linear AX3E2 is T-shaped

5 electron pairs What is there is 1 lone pair (invisible) Seesaw

5 electron pairs What is there are 2 lone pairs (invisible) T-shaped

VSEPR: Iodine Pentaflouride Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

Variations on Octahedral Shape AX6 is octahedral AX5E is square pyramidal AX4E2 is square planar For more lessons, visit www.chalkbored.com

All VSEPR shapes are based upon certain hybrids. sp2 hybrids make bent, trigonal planar. sp3 hybrids make water bent, trigonal pyramidal, and tetrahedral.

Bonding in H2 Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

Hybridization: sp Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

Hybridization: sp2 Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

Hybridization: sp3 Click in this box to enter notes. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.] Copyright © Houghton Mifflin Company. All rights reserved.

Resonance – molecular structures are actually the average of all equivalent structures of a molecule. Bond length - Single>double>triple