3.1 - Molecular orbitals Flashcards
what are formed when atomic orbitals combine
molecular orbitals
how many molecular orbitals are formed from two atomic orbitals combining?
2
what are the 2 types of molecular orbital formed from the combination of 2 atomic orbitals
a bonding and an antibonding orbital
which molecular orbital encompasses both nuclei
the bonding orbital
what is the basis of bonding between atoms
the attraction of the positively charged nuclei and the negatively charged electrons, in the bonding orbital.
how many electrons can a molecular orbital hold?
2
describe how the bonding orbital looks in a non-polar covalent bond
symmetrical about the
midpoint between two atoms
describe how the bonding orbital looks in a polar covalent bond
asymmetric about the midpoint between two atoms
describe how the bonding orbital looks in an ionic bond
the bonding molecular orbitals being almost entirely located around just one atom
what is a sigma bond
a molecular orbital formed by end-on overlap of atomic orbitals along the axis of the covalent bond
what is a pi bond
a molecular orbital formed by side-on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond
explain the process of hybridisation
mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals.
are hybrid orbitals degenerate
yes
what are the 3 hybrid orbitals that carbon can form
(4) sp³, (3) sp² and (2) sp orbitals
what spatial arrangement do sp³ orbitals form
tetrahedral
what spatial arrangement do sp² orbitals form
trigonal planar
what type of bonds do carbon hybrid orbitals form with other atomic orbitals
sigma bonds
in a carbon carbon double or triple bonds, what type of bond do the unhybridised orbitals form
pi bonds
what is the chemical formula for benzene
C₆H₆
how is a a ring of delocalised electrons formed in benzene
the unhybridised p orbitals on each carbon atom overlap side-on forming a pi molecular system, between all six carbon atoms.
what is the name for hydrocarbons containing a carbon-carbon triple bond
alkynes
what does HOMO stand for
highest occupied molecular orbital
what does LUMO stand for
lowest unoccupied molecular orbital
is the HOMO a bonding or antibonding orbital
bonding
do electrons usually fill bonding, or antibonding orbitals
bonding
what causes electrons to be promoted from HOMO to LUMO
absorption of electromagnetic radiation
why do most organic molecules appear colourless
the energy difference between HOMO and LUMO is relatively large, causing radiation emitted to be in the UV spectrum
what is a chromophore
the region of a molecule which determines its colour
chromophores exist in molecules containing what
a conjugated system
what is a conjugated system
a system of adjacent unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of carbon atoms. electrons are delocalised.
which molecules have a conjugate system
molecules with alternating single and double bonds, and aromatic molecules
what decreases the energy gap between HOMO and LUMO
the more atoms in the conjugated system
when does a compound appear coloured
when the wavelength of light absorbed is in the visible region (the compound will exhibit the complementary colour)
