Molecular Orbitals Flashcards
What can VSEPR not explain?
The bonding in all compounds.
Molecular orbital theory can provide?
An explanation for more complex molecules
Molecular orbitals form…
When atomic orbitals combine.
The number of molecular orbitals formed is equal to what?
The number of atomic orbitals that combine.
The combination of two atomic orbitals results in?
The formation of a bonding molecular orbital and an antibonding orbital.
The bonding molecular orbital encompasses?
Both nuclei
The attraction of the positively charged nuclei and the negatively charged electrons in the bonding molecular orbital is…
the basis of bonding between atoms.
Each molecular orbital can hold a maximum of how many electrons?
Two
In a non-polar covalent bond, the bonding molecular orbital is? About what point?
Symmetrical about the midpoint between two atoms.
Polar covalent bonds result from?
Bonding molecular orbitals that are asymmetric about the midpoint between two atoms.
The atom with the greater value for electronegativity has the…
Greater share of the bonding electrons.
Ionic compounds are an extreme case of? Where are bonding molecular orbitals located?
Asymmetry, with the bonding molecular orbitals being almost entirely located around just one atom, resulting in the formation of ions.
Molecular orbitals that form by end-on overlap of?
Atomic orbitals along the axis of the covalent bond are called sigma (σ) molecular orbitals or sigma bonds.
Molecular orbitals that form by side-on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond are called?
pi (𝜋) molecular orbitals or pi bonds.
The electronic configuration of an isolated carbon atom cannot explain?
The number of bonds formed by carbon atoms in molecules.
The bonding and shape of molecules of carbon can be explained by?
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.
In alkanes, the 2s orbital and the three 2p orbitals of carbon hybridise to? What arrangement do these adopt?
Form four degenerate sp3 hybrid orbitals. These adopt a tetrahedral arrangement.
The sp3 hybrid orbitals overlap how? To form?
End-on with other atomic orbitals to form bonds.
The bonding in alkenes can be described in terms of?
sp2 hybridisation.
The 2s orbital and two of the 2p orbitals hybridise to form? Which adopt what arrangement?
Three degenerate sp2 hybrid orbitals. These adopt a trigonal planar arrangement.
The hybrid sp2 orbitals overlap…
end-on to form bonds.
The remaining 2p orbital on each carbon atom of the double bond is? How does it lie?
unhybridised and lies perpendicular to the axis of the bond.
The unhybridised p orbitals overlap side-on to form?
Bonds
The bonding in benzene and other aromatic systems can be described in terms of?
sp2 hybridisation.
The six carbon atoms in benzene are arranged in what sort of structure?
A cyclic structure with bonds between the carbon atoms.
The unhybridised p orbitals on each carbon atom overlap side-on to form a… which extends?
molecular system, perpendicular to the plane of the bonds. This molecular system extends across all six carbon atoms. The electrons in this system are delocalised.
The bonding in alkynes can be described in terms of? What arrangement do these adopt?
sp hybridisation. The 2s orbital and one 2p orbital of carbon hybridise to form two degenerate hybrid orbitals. These adopt a linear arrangement.
The hybrid sp orbitals overlap.. How do the remaining orbitals lie?
end-on to form bonds. The remaining two 2p orbitals on each carbon atom lie perpendicular to each other and to the axis of the bond.
The unhybridised p orbitals overlap side-on to form?
Two bonds
Molecular orbital theory can be used to explain?
Why organic molecules are colourless or coloured.
Electrons fill bonding molecular orbitals, leaving?
Higher energy antibonding orbitals unfilled.
The highest bonding molecular orbital containing electrons is called?
the highest occupied molecular orbital (HOMO).
The lowest antibonding molecular orbital is called?
the lowest unoccupied molecular orbital (LUMO).
Absorption of electromagnetic energy can cause electrons to be?
Promoted from HOMO to LUMO.
Most organic molecules appear colourless because? Where is light absorbed?
The energy difference between HOMO and LUMO is relatively large. This results in absorption of light from the ultraviolet region of the spectrum
Some organic molecules contain?
Chromophores
A chromophore is? What’s it responsible for?
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.
Chromophores exist in molecules containing 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 within this conjugated system are delocalised.
Molecules with alternating single and double bonds, and aromatic molecules have?
conjugated systems.
The more atoms in the conjugated system the smaller the? What frequency of light is absorbed by the compound?
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.
Compounds highlighting the effect of increasing the length of…. Give an example?
The conjugated system on the colour can be compared. For example, vitamin A (yellow) can be compared with -carotene (orange).
Ninhydrin reacts with? Forming? What is this used in the detection of?
Amino acids and forms a highly conjugated product that absorbs light in the visible region, and an intense purple colour (λmax 750 nm) is observed. This is used in the detection of amino acids both as a locating agent in chromatography and in detecting latent fingerprints in crime scenes.
