Chemistry 8.3 8.3
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Transcript of Chemistry 8.3 8.3
Chemistry 8.3 8.3 Bonding Theories 8.3 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. Molecular Orbitals 8.3 How are atomic and molecular orbitals related? 8.3 Molecular Orbitals When two atoms combine, the molecular orbitalmodel assumes that their atomic orbitals overlapto produce molecular orbitals, or orbitals thatapply to the entire molecule. 8.3 Molecular Orbitals Just as an atomic orbital belongs to aparticular atom, a molecular orbitalbelongs to a molecule as a whole. A molecular orbital that can be occupied by twoelectrons of a covalent bond is called a bondingorbital. 8.3 Molecular Orbitals Sigma Bonds When two atomic orbitals combine to form amolecular orbital that is symmetrical around theaxis connecting two atomic nuclei, a sigmabond is formed. 8.3 A Sigma Bond Molecular Orbitals
Two s atomic orbitals can combine to form a molecular orbital, as in the case of hydrogen (H2 ). In a bonding molecular orbital, the electron density between the nuclei is high. 8.3 Molecular Orbitals When two fluorine atoms combine, the p orbitalsoverlap to produce a bonding molecular orbital.The FF bond is a sigma bond. Two p atomic orbitals can combine to form a sigma-bonding molecular orbital, as in the case of fluorine (F2). Notice that the sigma bond is symmetrical around the bond axis connecting the nuclei. 8.3 Molecular Orbitals Pi Bonds In a pi bond (symbolized by the Greek letter ),the bonding electrons are most likely to be foundin sausage-shaped regions above and below thebond axis of the bonded atoms. Pi-bonding Molecular Orbital
8.3 Molecular Orbitals Pi-bonding Molecular Orbital The side-by-side overlap of two p atomic orbitals produces a pi-bonding molecular orbital. Together, the two sausage-shaped regions in which the bonding electron pair is most likely to be found constitute one pi-bonding molecular orbital. 8.3 VSEPR Theory VSEPR Theory How does VSEPR theory help predictthe shapes of molecules? 8.3 VSEPR Theory The hydrogens in a methane molecule are atthe four corners of a geometric solid. All of theHCH angles are 109.5, the tetrahedralangle. Methane is a tetrahedral molecule. The hydrogens in methane are at the four corners of a regular tetrahedron, and the bond angles are all 109.5. Interpreting Diagrams How do the resulting HCH bond angles compare to the tetrahedral angle? 8.3 VSEPR Theory The valence-shell electron-pair repulsion theory,or VSEPR theory, explains the three- dimensional shape of methane. 8.3 VSEPR Theory According to VSEPR theory, therepulsion between electron pairscauses molecular shapes to adjustso that the valence-electron pairsstay as far apart as possible. The measured HNH bond angle is only 107.
8.3 VSEPR Theory The measured HNH bond angle is only107. An ammonia molecule is pyramidal. The unshared pair of electrons repels the bonding pairs. The measured bond angle in water is about 105.
8.3 VSEPR Theory The measured bond angle in water is about105. This comparison of water and carbon dioxide illustrates how unshared pairs of electrons can affect the shape of a molecule made of three atoms. a) The water molecule is bent because the two unshared pairs of electrons on oxygen repel the bonding electrons. b) In contrast, the carbon dioxide molecule is linear. The carbon atom has no unshared electron pairs. The carbon dioxide molecule is linear.
8.3 VSEPR Theory The carbon dioxide molecule is linear. This comparison of water and carbon dioxide illustrates how unshared pairs of electrons can affect the shape of a molecule made of three atoms. a) The water molecule is bent because the two unshared pairs of electrons on oxygen repel the bonding electrons. b) In contrast, the carbon dioxide molecule is linear. The carbon atom has no unshared electron pairs. Nine Possible Molecular Shapes
8.3 VSEPR Theory Nine Possible Molecular Shapes Shown here are common molecular shapes. 8.3 Hybrid Orbitals Hybrid Orbitals In what ways is orbital hybridizationuseful in describing molecules? 8.3 Hybrid Orbitals Orbital hybridization provides informationabout both molecular bonding andmolecular shape. In hybridization, several atomic orbitals mixto form the same total number of equivalenthybrid orbitals. Hybridization Involving Single Bonds
8.3 Hybrid Orbitals Hybridization Involving Single Bonds In methane, each of the four sp3 hybrid orbitals of carbon overlaps with a 1s orbital of hydrogen. Hybridization Involving Double Bonds
8.3 Hybrid Orbitals Hybridization Involving Double Bonds In an ethene molecule, two sp2 hybrid orbitals from each carbon overlap with a 1s orbital of hydrogen to form a sigma bond. The other sp2 orbitals overlap to form a carboncarbon sigma bond. The p atomic orbitals overlap to form a pi bond. Inferring What region of space does the pi bond occupy relative to the carbon atoms? Hybridization Involving Triple Bonds
8.3 Hybrid Orbitals Hybridization Involving Triple Bonds In an ethyne molecule, one sp hybrid orbital from each carbon overlaps with a 1s orbital of hydrogen to form a sigma bond. The other sp hybrid orbital of each carbon overlaps to form a carboncarbon sigma bond. The two p atomic orbitals from each carbon also overlap. Interpreting Diagrams How many pi bonds are formed in an ethyne molecule? Simulation 7 Compare sp, sp2, and sp3 hybrid orbitals.
The formula of a molecular compound indicates the numbers and kinds of atoms. The arrangement of the atoms within a molecule is called its molecular structure. Using Models Which of these molecules has the greatest number of oxygen atoms? 8.3 Section Quiz. 8.3. 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 thevalence electron pairs are attracted to each other. form molecules with only four possibleshapes. stay as far apart as possible. always form tetrahedral shapes. 8.3 Section Quiz. 3.Orbital hybridization provides informationabout both molecular bonding and molecularshape. both molecular bonding and bond energy. neither molecular bonding nor molecularshape. neither molecular bonding nor bondenergy. END OF SHOW