Chapter 08 - CHEMISTRY The Molecular Science Chapter Eight Click to edit Master subtitle style Bonding Covalent Covalent Bonding Present in

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Click to edit Master subtitle style CHEMISTRY The Molecular Science Chapter Eight Covalent Bonding
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Covalent Bonding Present in molecular compounds. Consists of sharing of one or more pairs of valence electrons to form a molecule. The attractive force between atoms. Why do atoms want to share electrons? G. N. Lewis: noble gases are chemically unreactive (except under extreme conditions) – due to their stable electron configuration. – Through covalent bonding each atom can attain a noble gas configuration. H:H H–H – represents a pair of shared electrons single covalent bond.
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Atomic Interactions atomic orbital overlap 1s 1s nuclear – electron nuclear – nuclear electron − electron attractive and repulsion forces are balanced
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H-H Bond Formation Decrease PE, increase stability Bond length = 74 pm Bond energy Bond energy = energy required to break molecule into separate atoms
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Shell Model of the Atom Lewis Symbol valence shell electrons = Group A # Sulfur S Group 6A 6 valence electrons . : S : . The number of covalent bonds an atom can form is determined by the number of electrons the atom must share to achieve a noble gas configuration. Octet Rule To form bonds, main group elements gain, lose, or share
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F2 14 valence electrons F – F : lone pair of electrons – shared bonding electrons (2) –single covalent bond Shared electrons are counted with each atom in a bond.
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Guidelines for Writing Lewis Structures 1. Add up the number of valence electrons in the molecule or ion, add electrons for each negative charge on ion and remove electrons for each positive charge. 2. Create a skeleton structure using the chemical symbols for the atoms and a line for bonding pairs of electrons. The element written first in the molecular formula is usually the central atom. H, O, and X are usually terminal atoms. 3. Place lone pairs of electrons around each terminal atom (except H – only 2 electrons) to satisfy the octet rule 4. All remaining electrons should be placed around central atom. 5. Add multiple bonds to central atom if there are less than eight electrons are around central atom. double bond = 2 shared pairs, triple bond = 3 shared pairs
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Problem 8.1 p. 339 Write the Lewis structures for a) NF3 b) N2H4 c) ClO4– Lewis structures do not give an accurate representation of where the electrons are. Based on orbital overlap (probability of finding an electron), there is a high probability of finding an electron between two nuclei. Lewis structures do not predict the geometry of the molecule.
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Lewis Structures of Hydrocarbons H CH4 methane H C H H H H CH3CH3 H C C H H H Electron Density Model Red – higher electron density – high probability. Blue – lower electron density.
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Single Covalent Bonds in Hydrocarbons Saturated hydrocarbons (contain C and H) – max. # of H – alkanes CnH2n+2 – contain C – C bonds CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3 Carbon can form strong bonds with other C atoms, H, O, N, S, X permits long chains to form.
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C C
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This note was uploaded on 10/03/2010 for the course CHE 131 taught by Professor Kerber during the Summer '08 term at SUNY Stony Brook.

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Chapter 08 - CHEMISTRY The Molecular Science Chapter Eight Click to edit Master subtitle style Bonding Covalent Covalent Bonding Present in

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