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Chemistry: Chapter 5
Valence Shell Electron Pair Repulsion Theory, Molecular Geometry, etc
| Question | Answer |
|---|---|
| bond angle | lines joining the centers of two atoms to the center of a third atom |
| VSERP model | a simple model that allows the prediction of molecular geometry; minimizes electron-electron repulsion |
| central atoms | any atom in a molecule that is bonded to more than one other atom |
| electron group | each lone pair |
| steric number | the number of electron groups |
| to determine the electron pair geometry... | draw a Lewis Structure and determine the steric number |
| electronic geometry | arrangement around the central atom minimize the electron-electron interactions for the given number of groups |
| molecular geometry | determined by the arrangement of atoms around the central atom depends on the electronic geometry |
| steps to determine molecular geometry | 1. start with the appropriate Lewis Structure 2. determine the appropriate electronic geometry 3. from the electronic geometry and the number of bonds, deduce the molecular geometry |
| equatorial sites | electrons around the equator of the molecule; interact with two electron groups |
| axial sites | electrons at the top and bottom of the molecule; interact with three electron groups |
| octahedral | all sites are equivalent |
| normal line | indicates a bond that is in the plane of the page |
| wedge | indicates a bond that comes out in front of the page |
| cross-hatched wedge | indicates a bond that goes back behind the the plane of the page |
| lone pair + lone pair = | greater repulsion |
| binding pair + bonding pair = | less repulsion |
| lone pair + bonding pair = | average/medium repulsion |
| lone pairs | cause bond angles to be smaller then the ideal 120 degree angle; they require more space; pushes shared pairs closer together |
| multiple bonds require more... | space than single bonds |
| double bonds force single bonds to do what? | move closer together |
| unequal sharing of electrons on two covalently bonded atoms leads to... | a partial positive charge on one atom and a partial negative charge on the other |
| each polar molecule can be treated as what? | a vector |
| two vectors of equal magnitude do what? | cancel each other |
| centers of positive and negative charge are coincident... | the molecule is non-polar |
| centers don't coincide | the molecule is polar |
| bond dipole | separation of electrical charge created when two atoms with different EN form a covalent bond |
| polar molecule | bond dipole vectors do not sum to zero; centers of positive and negative do not coincide |
| dipole moment | a quantitive expression of the polarity of a molecule; non-polar molecules will not have one of these |
| non-polar molecule | the electron groups are symmetrically aligned |
| polar molecule | the electron groups are not symmetrically aligned |
| valance bond theory | a bond will form between two atoms when an orbital of one atom occupies the same region of space as an orbital of another atom overlap one another, or a pair of electrons simultaneously occupies both orbitals; basically a covalent bond |
| the strength of the valance electron bond depends on what? | the degree of the overlap |
| orbitals overlap only in particular directions to maximize... | overlap (not including s orbitals) |
| orbitals have a... | specific bond directionality |
| moving electrons from the s to the p orbital requires... | energy |
| promotion | occurs in Carbon, because it almost always has 4 orbitals |
| 2p and 2s orbitals may mix resulting in 4... | hybrid orbitals |
| hybrid orbitals | equivalent to each other in all respects |
| hybrid orbitals formed equals | number of atomic orbitals mixed |
| s orbitals can mix with what orbitals to form hybrid orbitals? | p and d |
| steric number | valance electrons + the bonded electrons |
| one hybrid orbital is required for... | atoms to bond to other atoms |
| sigma bond | has cylindrical symmetry about the bond axis and results from the head-to-head overlap of two orbitals; one sigma bond in double bonds & one sigma bond in each carbon hydrogen bond; one sigma bond in a triple bond |
| pi bond | electron density above and below a plane that contains the bond axis, and results from side-to-side overlap of parallel p or d orbitals; one pi bond in a double bond; two pi bonds in a triple bond |
| pi bonds... | lock the structure of the molecule, so they can freely rotate around the single bond, but not the double bond |
| cis isomer | same side C-C bonds |
| trans isomer | the Carbons are found on different sides of the molecule |
| molecular orbital theory | a more sophisticated approach to chemical bonding than Lewis Structures and valence bond theory; can explain more properties than the other two |
| paramagnetic | when an atom has one or more paired electrons |
| molecular orbitals | regions of space where there is a high probability of finding an electron; often delocalized over two or more atoms |
| bond order | 1/2(# bonding electrons - # anti bonding electrons) |
| bonding | sigma |
| anti-bonding | sigma* |
| molecular orbital guidlines | 1. orbitals of the same energy and shape mix together better than those that don't have the same energy and shape 2. MO can accommodate 2 electrons 3. electrons fill MOs according to Hund's rule |
| hund's rule | for two atomic orbitals to combine and form molecular orbitals, the symmetry of the orbitals has to be the same and there needs to be a reasonable energy match |
| homonuclear diatomic molecule | a diatomic molecule which is composed of two like atoms; H2, O2, F2, etc |
| heteronuclear diatomic molecule | a diatomic molecule which is composed of two unlike atoms; HF, CO, etc; energies of corresponding atomic orbitals may differ appreciably |
| delta+ | a lesser concentration of electrons on the atom |
| delta- | a large concentration of electrons on the atom; compound will be polar |
| electrons neither contribute nor detract from what? | the stability of the bonding |
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livabirch4
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