Ch. 11 - Molecular Shape and Bonding Theories + VSEPR

steric number = 2

• 1 structure

• linear, linear

• 180°

• no lone pairs 

linear, linear (SN = 2)

• 180°

• no lone pairs

steric number = 3

• 2 structures 

• trigonal planar, 120°

• trigonal planar, bent, <120°, 1 lone pair

trigonal planar, trigonal planar

• SN = 3

• 120°

• no lone pairs

trigonal planar, bent

• SN = 3

• < 120°

• one lone pair

steric number = 4

• 3 structures

• tetrahedral, tetrahedral, 109.5°, no lone pair

• tetrahedral, trigonal pyramid, < 109.5, 1 lone pair

• tetrahedral, bent, <<109.5°, 2 lone pair

tetrahedral, tetrahedral 

• SN = 4

• 109.5°

• no lone pair

tetrahedral, trigonal pyramid

• SN = 4

• < 109.5°

• 1 lone pair 

tetrahedral, bent (SN = 4)

• << 109.5°

• 2 lone pairs

steric number = 5

• 4 structures 

• trigonal bipyramid

• trigonal bipyramid, seesaw

• trigonal bipyramid, t-shape

• trigonal bipyramid, linear 

trigonal bipyramid, trigonal bipyramid

• SN = 5

• between dashed and wedged - 120°

• between X and X - 90°

• between another X and X - 180°

• no lone pair 

trigonal bipyramid, seesaw

• SN = 5

• between dashed and wedged - < 120°

• between X and X - < 90°

• between X and lone pair - < 180°

• 1 lone pair

t-shape (SN = 5)

• between X and X - < 90°

• between another X and X - < 180°

• 2 lone pairs

trigonal bipyramid, linear

• SN = 5

• 180°

• 3 lone pairs

steric number = 6

• 5 structures 

• octahedral, octahedral

• octahedral, square pyramid

• octahedral, square planar

• octahedral, t-shape

• octahedral, linear 

octahedral, octahedral

• SN = 6

• between X and dashed - 90°

• 2 wedged and 2 dashed atoms 

• no lone pairs

• 180°

octahedral, square pyramid

• SN = 6

• between dashed and wedged - < 90°

• between dashed and X - < 90°

• < 180°

• 2 dashed and 2 wedged

• 1 lone pair

octahedral, square planar

• SN = 6

• 2 dashed and 2 wedged

• 2 lone pair

• 90° between wedged and dashed 

• 180°

octahedral, t-shape

• SN = 6

• 2 wedged and 2 dashed

• < 90° between wedged and X

• 180°

• 3 lone pair

octahedral, linear

• 2 wedged and 2 dashed 

• 180° 

• 4 lone pair 

isomers

different compounds with the same molecular formula

flash point

temperature at which vapor of a liquid fuel can be ignited

valence shell electron pair repulsion model (VSEPR)

model that uses the number of e- domains around a central atom to predict the most stable shape occupied by the domain due to repulsion

electron domain

a charge cloud around a central atom. can be any of these: lone pairs, single unshared e-, single, double, triple bonds

electron geometry

shape determined by the number of electron domains; most stable arrangement

molecular geometry

3-D shape of a molecule

polar molecule

a molecule with asymmetric e- distribution; molecular dipole 

non-polar molecule

a molecule with symmetric e- distribution; no dipole

valence bond theory

theory that explains bonding by the overlap of atomic orbitals and hybridization of atomic orbitals

sigma bond

covalent bond formed by head-to-head overlap of orbitals along the internuclear axis

• a single bond

pi bond

covalent bond formed by side-by-side overlap of hybridized p orbital above and below the internuclear axis

• found in triple and double bonds 

hybrid orbitals

mathematical combination s of the standard atomic orbitals that result in maximal overlap in bonds 

sp3 hybridization

• hybrid orbitals formed from one s orbital and 3 p orbitals

• central atom surrounded by 4 regions of e- density

• tetrahedral geometry

sp2 hybridization

• hybrid orbitals formed from 1 s orbital and 2 p orbital

• central atom surrounded by 3 regions of the e- density

• trigonal planar geometry

sp hybridization

hybrid orbitals formed when one s orbital and one p orbital 

central atom has no lone pairs of e- in linear arrangement 

conformation

various shapes possible for larger molecules due to rotation around single bonds 

molecular orbital theory (MO)

theory that explains bonding by the combination of atomic orbitals to form bonding molecular orbitals and antibonding molecular orbitals

delocalized

e- that are shared across multiple atoms within a molecule, rather than being confined to a single bond 

bonding orbitals

lower energy molecular orbitals resulting from additive combinations of atomic orbitals 

antibonding orbitals 

a higher energy molecular orbital resulting from the subtractive combination of atomic orbitals (designated by *)

nonbonding orbitals

orbitals occupied by lone pairs in MO diagrams

constructive interference

waves combine in phase to increase peaks and decrease troughs; a phenomenon where two or more waves combine to produce a wave with a larger amplitude than the individual waves 

destructive interference

waves combine out of phase to cancel peaks and troughs; resulting in reduced or even zero amplitude

molecular orbital (MO) diagram

shows the relative energy levels to form binding molecular orbitals and antibonding molecular orbitals

bond order formula

B.O = BE - ANE/2

higher bond order

represents stronger, shorter, and more stable bonds

B.O < 0

indicates and unstable molecular that is unlikely to form 

paramagnetism

weak attraction to a magnetic field; property of molecules with unpaired e- 

diamagnetism

very slight repulsion for a magnetic field; property of molecules with all paired e- 

what does MO theory describe?

it describes resonance as a delocalization of the pi bond among adjacent atoms