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Chemistry 8.3. 8.3. Section 8.3-1. Bonding Theories. 8.3-1. This car is being painted by a process called electrostatic spray painting. The negatively charged droplets are attracted to the auto body. You will learn how attractive and repulsive forces influence the shapes of molecules. 8.3-1.
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Chemistry 8.3 8.3 Section 8.3-1
Bonding Theories 8.3-1 • This car is being painted by a process called electrostatic spray painting. The negatively charged droplets are attracted to the auto body. You will learn how attractive and repulsive forces influence the shapes of molecules.
8.3-1 Molecular Orbitals • Molecular Orbitals • How are atomic and molecular orbitals related?
8.3-1 Molecular Orbitals • When two atoms combine, the molecular orbital model assumes that their atomic orbitals overlap to produce molecular orbitals, or orbitals that apply to the entire molecule.
8.3-1 Molecular Orbitals • Just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole. • A molecular orbital that can be occupied by two electrons of a covalent bond is called a bonding orbital.
8.3-1 VSEPR Theory • VSEPR Theory • How does VSEPR theory help predict the shapes of molecules? First of all, what is VSEPR? V is for Valence S is for Shell E is for Electron P is for Pair and R is for Repulsion
8.3-1 VSEPR Theory • The valence-shell electron-pair repulsion theory, or VSEPR theory, explains the three-dimensional shape of methane.
8.3-1 VSEPR Theory • According to VSEPR theory, the repulsion between electron pairs (either unshared or bonded) causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.
8.3-1 VSEPR Theory • There are nine (9) possible Molecular Shapes. The five (5) most important ones that we will be studying are Linear, Trigonal Planar, Bent, Pyramidal, and Tetrahedral. • We will now discuss these.
8.3-1 VSEPR Theory • The hydrogen atoms in a methane molecule are at the four corners of a geometric solid. All of the H—C—H angles are 109.5°, and this shape is called tetrahedral. In this bonded pair, there are four (4) bonded pairs and zero (0) unshared pairs on the main carbon atom.
8.3-1 VSEPR Theory • For ammonia, NH3, the measured H-N-H bond angle is only 107°. This shape is called Pyramidal. It is different from the methane C-H-C bond angle (tetrahedral) because of the unshared pair of electrons residing on the nitrogen atom all the time. This is different from the electron pairs in bonds, which are shared and hence, split their time between two atoms.
8.3-1 VSEPR Theory • The measured bond angle in water is about 105° It’s shape is called “Bent”. Water has this shape due to its two (2) pairs of unshared electrons and its two bonds with hydrogen.
8.3-1 VSEPR Theory • The carbon dioxide (CO2) molecule is Linear, which means that it’s O-C-O bond angle is 180°. Note the difference between water (H2O) and CO2. They both have the same relative formula, but different shapes. That is because of the two unshared pairs of electrons on the oxygen atom in water.
8.3-1 VSEPR Theory • The final shape to be studied is called Trigonal Planar. An example of this is BF3 with it’s F-B-F bond angle of 120°. Note that with this molecule, the shape is totally in one plane or 2-dimensional, like the linear shape. With boron, there are no unshared pairs of electrons to alter its shape like with water.
8.3-1 VSEPR Theory Molecular Shapes Summary
8.3 Section Quiz. • 1. A molecular orbital belongs to a • specific atom. • molecule as a whole. • specific pair of atoms. • central atom.
8.3 Section Quiz. • 2. VSEPR theory enables prediction of 3-dimensional molecular shape because the valence electron pairs • are attracted to each other. • form molecules with only four possible shapes. • stay as far apart as possible. • always form tetrahedral shapes.
