Chp 1—Covalent bonding & shapes of molecules Flashcards
vitalism
belief that organic compounds must come from a living source
disproved vitalism
Wohler - 1828 - synthesized urea
each shell holds _____ electrons
2n2
n = shell #
shells divided into…
names
orbitals
s — 1/shell
p — 3/shell 2+
d — 5/shell 3+
3 rules for filling of shells
Aufbau principle
Pauli exclusion principle
Hund’s rule
Aufbau principle
lower energy orbitals are filled first
Pauli exclusion principle
only 2 electrons per orbital, and they must spin on their axes in opposite directions
Hund’s rule
in orbitals of equal energy level, each is singly occupied before any is doubly occupied
Pauling scale measures…
electronegativity
electronegativity difference definition of ionic, polar covalent, and nonpolar covalent bonds
ionic: >1.9 difference in EN
polar: 0.5-1.9 difference in EN
nonpolar: <0.5 difference in EN
nitrogen normal bonding patterns
N with 3 single bonds and 1 lone pair
oxygen normal bonding pattern
O with 2 single bonds and 2 lone pairs
halogen normal bonding pattern
Cl with 1 single bond and 3 lone pairs
exceptions to octet rule
- 3rd row elements (from either side) - have d orbitals
- small atoms - ex boron forms 3 single bonds
formal charge =
FC = # VE in neutral unbonded atom - (all unshared electrons + ½ of shared electrons)
+ FC =
atoms’ electrons in molecule < VE in unbonded atom
– FC =
atoms’ electrons in molecule > VE in unbonded atom
all H have __ formal charge
0
resonance structures occur especially in molecules with…
𝝅 bonds
rules for drawing resonance structures (5)
- only electrons move, not atoms
- obey rules of covalent bonding; 3rd period atoms may have up to 12 electrons in shells
- keep track of lone pairs & formal charges; all structures must have same number of paired and unpaired electrons
- use curved arrows to interconvert & ID structures
- use double headed arrow between structures
resonance stabilization
energy of the true hybrid is << the energy of any contributing structure
orbitals with same energy
degenerate
overlap model of bonding includes 2 bond types…
sigma bonds (𝝈)
pi bonds (𝝅)
possible sigma bonds by orbital type
s + s
s + p
px + px
possible pi bonds based on orbital type
py + py
pz + pz
stronger type of overlap bond
sigma
hybridization occurs with…
orthogonal oriented orbitals (no overlap)
conservation of orbitals
of originals = # of hybrids
total orbitals in sp3 hybridization of carbon
1 original (1s)
4 hybrids (2sp3)
components of sp3 hybrid
1 s (25%)
3 p (75%)
shape of an s + p hybridization
1 large lobe, 1 small back lobe (not drawn)
drawn orbitals around sp3-hybridized C
bond angle
4, all sp3 hybrids
109.5°
total orbitals in sp2 hybridization of carbon
1 original (1s)
3 hybrids (2sp2)
1 unhybridized (2p)
drawn orbitals around sp2 hybridized C
bond angle
4 — 3 sp2 hybrids, 1 unhybridized p
120°
shape of sp2 hybridized C
trigonal planar
hybrid orbitals form ___ bonds, unhybridized orbitals form ____ bonds
sigma
pi
total orbitals in sp hybridization
1 original (1s)
2 hybrids (2sp)
2 unhybridized (2p)
drawn orbitals around sp-hybridized C
bond angle
4 — 2 sp hybrids, 2 unhybridized p
180°
shape of sp hybridized C
linear
components of sp2 hybrid
1 s (33%)
2 p (67%)
components of sp hybrid
1 s (50%)
1 p (50%)
constitutional isomers
different connectivity between atoms
cis-trans isomerism arises from…
pi restriction of free rotation
cis trans isomers are stable at _____ because ______
room temp
requires energy to change their form
wave function
mathematical description of wave size, shape, orientation
node
amplitude of the wave is 0 at the origin
there is 0 chance of finding an electron
atomic orbital
unhybridized orbitals on an atom
linear combination of atomic orbitals
hybridization
wave functions are combined
molecular orbital
combination of atomic orbitals from different atoms
constructive interference occurs when…
molecules collide at an orientation with e- in the same phase
bonding molecular orbitals’ nodes vs antibonding
antibonding always have 1 more node
molecular orbitals vs atomic orbitals in energy
energy of MOs << energy of AOs
strength of pair repulsion vs bonded pair repulsion
lone pair repulsion >> bonded pair repulsion
shape vs geometry
shape does not consider lone pairs
geometry considers lone pairs
