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70 Cards in this Set
- Front
- Back
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Lewis structures vs molecular models |
Molecular models show 3D arrangement |
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Bond angle |
Angle defined by covalent bonds between 3 adjacent atoms |
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Angle defined by covalent bonds between 3 adjacent atoms |
Bond angle |
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molecular geometry
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shape defined by lowest energy 3D arrangement of atoms
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shape defined by lowest energy 3D arrangement of atoms
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molecular geometry |
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VSEPR Theory
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geometric arrangement of bonding electron pairs around atoms based on minimizing repulsion energy
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geometric arrangement of bonding electron pairs around atoms based on minimizing repulsion energy |
VSEPR Theory
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Electron pair geometry
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spatial arrangement of bonding electron pairs AND lone pairs (non-bonding) of valence electrons
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spatial arrangement of bonding electron pairs AND lone pairs (non-bonding) of valence electrons
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electron pair geometry
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molecular geometry
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defined by relative arrangement of atoms (bonding pairs) in a molecule ignores lone pairs bond angles depend on electron pair repulsion |
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defined by relative arrangement of atoms (bonding pairs) in a molecule and ignores lone pairs
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molecular geometry
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steric number
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number of atoms bonded to central atom + number of lone pairs on central atom
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number of atoms bonded to central atom + number of lone pairs on central atom
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steric number
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between 3 different bonds with lone pairs and bonding pairs, which has greatest electron pair repulsion? and 2nd and last?
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lone pair - lone pair = greatest repulsion lone pair - bonding pair next bonding pair - bonding pair = least repulsion |
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double bonds electron pair repulsion in comparison to single bonds
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double bonds experience more repulsion than single bonds
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bond angles for central atom in comparison to repulsive forces
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bond angles around central atom decrease as repulsive forces increase (w/ lone pairs, bond angles shrink a little) |
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SN = 2
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electron pair geometry - linear molecular geometry - linear bond angle: 180 |
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SN = 3
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electron pair geometry - trigonal planar molecular geometry - trigonal planar, bent bond angle: 120 |
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SN = 4
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electron pair geometry - tetrahedral molecular geometry - tetrahedral, trigonal pyramidal, bent bond angle: 109.5, <109.5, <<109.5 |
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SN = 5
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electron pair geometry - trigonal bipyramidal molecular geometry - trigonal bipyramidal, seesaw, T-shaped, linear bond angle: 120 on center axis, 90 from center to top |
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SN = 6
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electron pair geometry - octahedral molecular geometry - octahedral, square pyramidal, square planar, T-shaped, linear |
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dipole moment
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a measure of the degree of charge separation in a molecule
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a measure of the degree of charge separation in a molecule
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dipole moment
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how is dipole moment observed
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measurements are based on the fact that polar molecules are oriented by an electric field; this orientation affects the capacitance of the charged plates that create the electric field
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Requirements for a polar molecule:
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1) molecules must contain polar bonds 2) orientation of polar bonds results in charge separation from one part of molecule to another (asymmetric) |
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bond dipole
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separation of charge within a covalent bond
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separation of charge within a covalent bond
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bond dipole
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polar molecule |
have nonzero dipole moments vectors of bond dipoles sum > zero |
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what molecules have nonzero dipole moments
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polar molecule
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polarity and boiling point
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attractive forces due to polarity lead the molecule to have a higher boiling point
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cis vs trans compounds
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trans have same elements on opposite sides, no net polarity, nonpolar molecule cis have elements on same sides, net polarity is up or down, polar molecule |
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dipole moment
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measured value defining extent of separation of + and - charge centers in a molecule
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measured value defining extent of separation of + and - charge centers in a molecule
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dipole moment
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dipole moment in accordance with polarity
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higher dipole moment = more polar
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valence bond theory
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assumes that covalent bonds form when orbitals on different atoms overlap
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assumes that covalent bonds form when orbitals on different atoms overlap
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valence bond theory
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hybridization
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mixing of atomic orbitals to generate new sets of orbitals that form covalent bonds with other atoms
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mixing of atomic orbitals to generate new sets of orbitals that form covalent bonds with other atoms
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hybridization
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hybrid atomic orbital
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one of a set of equivalent orbitals created when specific atomic orbitals are mixed
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one of a set of equivalent orbitals created when specific atomic orbitals are mixed
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hybrid atomic orbitals
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sp geometric arrangement
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linear
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sp2 geometric arrangement
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trigonal planar
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sp3 geometric arrangement
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tetrahedral
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sp3d geometric arrangement
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trigonal bipyramidal
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sp3d2 geometric arrangement
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octahedral
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sigma bond
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covalent bond having highest electron density between the 2 atoms along the bond axis
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covalent bond having highest electron density between the 2 atoms along the bond axis
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sigma bond
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pi bond
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electron density is concentrated above/below the bonding axis
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electron density is concentrated above/below the bonding axis
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pi bond
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explain sigma bond
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a "head to head" overlap of orbitals with a cylindrical shape about the bond axis occurs when 2 "s" orbitals overlap or "p" orbitals overlap along their axis |
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explain pi bond
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"side to side" overlap of parallel "p" orbitals, creating an electron distribution above and below the bond axis
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bond rotation with sigma bonds
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because orbitals that form sigma bond point along internuclear axis, rotation around that bond does not require breaking the interaction between orbitals
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bond rotation with pi bonds
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orbitals that form pi bonds interact above and below internuclear axis, so rotation around the axis requires breaking of the interaction between the orbitals
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examples of bond rotation with pi bonds
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the geometric patters are fixed into either cis or trans
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problems with lewis structures/valence bond theory
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modeled bonding capacities of the elements, but did not accounts for molecular shapes
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problems with VSEPR and valence bond theories:
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account for observed molecular geometries, but not magnetic properties |
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molecular orbital theory
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wave functions of atomic orbitals in atoms are combined to create molecular orbitals (MOs) in molecules number of molecular orbitals formed = number of atomic orbitals combined molecular orbitals spread out over entire molecule |
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types of molecular orbitals:
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bonding orbitals antibonding orbitals |
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bonding orbitals
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hole atoms together by increasing electron density between nuclear centers in molecules are lower in energy (more stable) than atomic orbitals from which they are formed |
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hole atoms together by increasing electron density between nuclear centers in molecules
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bonding orbitals
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antibonding orbitals
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destabilize the molecule because they do not increase electron density between nuclear centers are higher in energy (less stable) than atomic orbitals from which they are formed |
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destabilize the molecule because they do not increase electron density between nuclear centers
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antibonding orbitals
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MO diagram
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energy level diagram for molecular orbitals; shows formation of bonding/antibonding orbitals
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energy level diagram for molecular orbitals; shows formation of bonding/antibonding orbitals
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MO diagram
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MO diagram using two 1s orbitals
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yields 2 sigma MOs (1 bonding/1 antibonding) antibonding (w/ star) is shown above bonding |
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bond order when using MO diagram
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bond order = (1/2 # bonding electrons) - (1/2 # antibonding electrons)
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MO diagram (larger)
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same sigma on the bottom half with antibonding above bonding then there are (in order of bottom to top for upper half) 2 pi bonding, 1 sigma bonding, 2 pi antibonding, 1 sigma antibonding |
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paramagnetism |
atoms or molecules having unpaired electrons are attracted to magnetic fields
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atoms or molecules having unpaired electrons are attracted to magnetic fields
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paramagnetism
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dimagnetism
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atoms or molecules having all paired electrons are repelled by magnetic fields
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