More revision Flashcards
How do molecular orbitals form?
Molecular orbitals form when atomic orbitals combine
What happens to the molecular orbitals in non-polar covalent bonds?
In a non-polar covalent bond, the bonding molecular orbital is symmetrical about the
midpoint between two atoms
What happens to the molecular orbitals in polar covalent bonds?
Polar covalent bonds result from bonding molecular orbitals that are asymmetric about the midpoint between two atoms
What does the combining of two atomic orbitals form?
The combination of two
atomic orbitals results in the formation of a bonding molecular orbital and an antibonding
orbital
What does the bonding molecular orbital encompass?
encompasses both nuclei.
What does the antibonding molecular orbital have?
Has higher energy arrangement and are normally empty but they can be occupied when the bonding orbitals are full or the electron is excited to a higher energy.
How are sigma bonds formed?
Molecular orbitals that form by end-on overlap of atomic orbitals along the axis of the
covalent bond
How are pi bonds formed?
Molecular orbitals that form by side-on overlap of parallel atomic orbitals that lie
perpendicular to the axis of the covalent bond
What is hybridisation?
Hybridisation is the process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals. These hybrid orbitals are degenerate
What contains sp3 hybridisation?
single bonds between atoms
What is sp3 hybridisation
the 2s orbital and the three 2p orbitals of carbon hybridise to form four degenerate sp3 hybrid orbitals
What contains sp2 hybridisation?
double bonds between atoms
What is sp2 hybridisation
The 2s orbital and two of the 2p orbitals hybridise to form three degenerate sp2 hybrid orbitals
What contains sp hybridisation?
triple bonds between atoms
What is sp hybridisation
The 2s orbital and one 2p orbital of carbon hybridise to form two degenerate hybrid orbitals
How do electrons fill molecular orbitals?
Electrons fill bonding molecular orbitals, leaving higher energy antibonding orbitals unfilled
What does HOMO stand for?
The highest bonding molecular orbital containing electrons is called the highest occupied molecular orbital (HOMO)
What does LUMO stand for?
The lowest antibonding molecular orbital is called the lowest unoccupied molecular orbital (LUMO)
How does colour arise in molecular orbitals?
Absorption of electromagnetic energy can cause electrons to be promoted from HOMO to LUMO.
What are chromophores?
A chromophore is a group of atoms within a molecule that is responsible for absorption of light in the visible region of the spectrum. Light can be absorbed when electrons in a chromophore are promoted from the HOMO to
the LUMO.
What are conjugated systems?
Electrons within this conjugated system are delocalised. Molecules with alternating single and double bonds, and aromatic molecules have conjugated systems
What does more conjugated systems result in?
the smaller the energy gap between HOMO and
LUMO. A lower frequency of light (longer wavelength, lower energy) is absorbed by the
compound. When the wavelength of light absorbed is in the visible region, the compound
will exhibit the complementary colour
What does less conjugated systems result in?
The greater the energy gap between the HOMO and the LUMO.
