Chapter 3: Bonding Flashcards
Describe the appearance of s-, p-, and d-orbitals
The 4 principle quantum numbers
principle quantum number (n)
azimuthal quantum number (l)
magnetic quantum number (ml)
spin quantum number (ms)
principal quantum number (n)
a measure of SIZE (proximity to the nucleus)
possible values: 1 to infinity
indicates the energy level of an electron within the orbital
smaller # = closer to nucleus
azimuthal quantum number (l)
indicate the SHAPE of the sub shells within an electron shell (n)
possible values: 0 to n-1
larger l value = higher energy
s orbital
l = 0
spherical shape
p orbital
l = 1
dumbell shape
magnetic quantum number (ml)
indicates the ORIENTATION of the sub shell
possible values: -l to +l
spin quantum number (ms)
indicates the SPIN of electrons within a given shell
possible values: +/- ½
molecular orbitals
the resulting orbital when 2 atomic orbitals combine
bonding orbital
the signs of the wave functions of the combining atomic orbitals are the SAME
lower-energy (more stable)
antibonding orbital
the signs of the wave functions of the combining atomic orbitals are DIFFERENT
higher-energy (less-stable)
How are molecular orbitals obtained (mathematically)?
by adding or subtracting the wave functions of the atomic orbitals
If n atomic orbitals combine, how many molecular orbitals result?
n
(the number of orbitals must be conserved!)
explain the energy diagram with atomic orbitals to molecular orbitals
electrons found in the bonding orbital will …
stabilize the bond and hold the atoms together
electrons found in the anti bonding orbitals will…
cause dissociation of the atoms
sigma bonds (3)
all single bonds are sigma bonds (hold 2 electrons)
results when a MO is formed by head-to-head or tail-to-tail overlap of atomic orbitals
single bonds allow free rotation of atoms around the bond
pi bonds (4)
when 2 p-orbitals line up side-by-side
a double bond consists of one pi bond on top of an existing sigma bond
a triple bond consists of 1 sigma bond and 2 pi bonds
double and triple bonds do NOT allow free rotation of atoms around the bond
strength of sigma and pi bonds
sigma bonds are stronger than individual pi bonds
the strength of the bonds are additive, making double and triple bonds stronger than single bonds
bond energy
energy required to break a bond
indicates the STRENGTH of a bond
higher bond energy = stronger bond
hybridization
the concept of mixing two atomic orbitals to give rise to a new type of hybridized orbitals
how are hybrid orbitals formed?
by mixing different types of orbitals
sp3 orbitals
formed by combining 3 p orbitals and 1 s orbital
have a new, unique hybridized shape
ex. calculating “s character” of an sp3 bond
an sp3 bond is the combination of 1 s orbital and 3 p orbitals (4 total)
1 s / 4 total = 25% s character
degenerate orbitals
orbitals which have the same energy
hybrid orbitals are used to form _______ bonds
sigma bonds
unhybridized orbitals are used to form ______ bonds
pi bonds
s character and p character of sp3 hybridized orbitals
s character: 25%
p character: 75%
s character and p character of sp2 hybridized orbitals
s character: 33%
p character: 66%
s character and p character of sp2 hybridized orbitals
s character: 50%
p character: 50%
carbons with all singles bonds are ____ hybridized
sp3
carbons with one double bond are ____ hybridized
sp2
(1 unhybridized p orbital is involved in the pi bond)
carbons with 1 triple bond are ____ hybridized
sp
(2 unhybridized p orbitals are involved in pi bonds)
determine hybridization of atoms
of pi bonds will equal the # of unhybridized p orbitals
of sigma bonds or lone pairs will equal the # of hybridized orbitals
(“groups” = bonds and lone pairs)
resonance
describes the delocalization of electrons in molecules that have conjugated bonds
a way of describing bonding in certain molecules by the combination of several contributing structures into a resonance hybrid in valence bond theory
conjugation
occurs when single and multiple bonds alternate, creating a system of unhybridized p-orbitals down the backbone of the molecule through which pi electrons can delocalize
why are sigma bonds stronger than pi bonds?
they have more orbital overlap
