Flashcards in unit two - molecular structure Deck (27):
what is the empirical formula ?
the elements in a compound are shown as a simple ratio
what is the molecular formula ?
this shows the actual number of each element in a compound.
what is the skeletal structure ?
when end of a line represents a carbon.
what is the molecular orbital model ?
this diagram represents chemical bonding
what do electrons in atoms occupy ?
what do electrons in molecules occupy?
when is a molecular orbital full ?
when it contains 2 electrons that have opposite spins.
how are molecular orbitals generated ?
by combining atomic orbitals
what is the link between the number of atomic orbitals and molecular orbitals ?
they are always the same number of each.
is a bonding molecular orbital high or low in energy ?
low in energy
what holds a bonding molecular orbital together ?
the attraction between the positive nuclei and the negatively charged electrons.
is an anti bonding molecular orbital high or low in energy and why?
high in energy , this is due to it containing no electrons, therefore repulsion occurs and the higher energy occurs.
does the anti bonding molecular orbital have electrons ?
no it is empty.
how is a sigma bond formed ?
due to end on overlap of atomic orbitals.
where are sigma bonds present ?
only in alkanes.
how is a pi bond formed ?
when atomic orbitals overlap side on.
where are pi bonds present ?
in molecules that form multiple bonds, such as alkenes.
what bond is stronger , a pi bond or sigma and why ?
A sigma bond , as end on overlap of atomic orbitals is more effective than side on overlap of atomic orbitals.
Does the double bond in alkenes contain a sigma bond ?
yes all the carbon to h bonds and c-c but the c=c has the pi bond and the other is sigma.
what is hybridisation ?
the process of mixing atomic orbitals to form new orbitals that are called hybrid orbitals.
what is unusual about the c in methane?
the electron configuration of carbon reveals that c has 2 unpaired electrons , so it would be expected to form 2 bonds. However in methane carbon forms 4 bonds. how does this occur when carbon only has 2 unpaired electrons ?
what could occur to result in carbon forming 4 bonds?
promote one of the electrons from 2s to 2p as this would result in 4 unpaired electrons and as a result it could form 4 bonds.
However a more satisfactory explanation is hybridisation. It would be Hybridise one 2s orbital with 3 2p orbitals to form 4 hybrid orbitals called , sp3.
does hybridisation occur in alkenes ?
yes one 2s orbital mixes with 2 2p orbitals to form 3 sp2 hybrid orbitals and one 2p orbital is left un hybridised and can form a pi bond.
characteristics of sp3 orbitals in alkanes. ?
they are degenerate and identical in shape. All 4 sp3 orbitals are half filled.
characteristics of a non polar or pure covalent bond?
This is when there is no difference between the electronegativity between the atoms. Therefore the bonding molecular orbital is completely symmetrical around the midpoint of the bond.
characteristics of polar covalent bond ?
This is when there is a difference in electronegativity between atoms. Therefore the bonding molecular orbtial is asymmetrical and skewed towards the most electronegative atom in bond.