Molecular shape and bonding Flashcards
Ionic Bonding
metal and non metal
transfer of electrons
Covalent Bonding
non metal and non metal
stare of electrons
Metalic Bonding
metal and metal
electrons pooled
Why do chemical bonds form?
because they lower the potential energy between the charged particles that constitute atoms.
What is Lewis Theory?
The valence electrons (outer) are held most loosely and hence used in bonding.
Elements in same column have same properties bc they have the same number of valence electrons.
What is the Octet Rule?
8 - is the most stable configuration for most atoms.
Atoms with transfer/share electrons to reach this.
Ionisation energy…
energy required to remove the electron.
Elements with low ionisation energies are..
electropositive.
Elements that readily acquire electrons are…
electronegative.
Lewis theory was not good at…
explaining other data e.g. the rigidity of carbon-carbon double bonds.
heisenberg uncertainty principle says…
The position and speed of electrons are complementary.
If we know one accurately, we can’t know the other accurately.
How are each orbits represented according to mathematical calculations?
1s - a small sphere
electron can be found anywhere
2s - a larger sphere
contains a node
What is the radial node?
Found in 2s orbital - a region where the probability of finding the electron falls to zero.
De Broglie
electrons have both particle-like and wave-like properties.
The node is a result of…
the wave-like behaviour of electrons.
Imagine plucking a guitar string…
Wave function (+) is the region above the rest position and (-) is below it.
Where is the node on a guitar string?
The region where the amplitude (maximum displacement) of the standing wave is zero.
What are the shapes of the p-orbitals?
Dumbbell shaped.
They have a nodal plane that cuts the dumbbell into two lobes.
There are three degenerate p atomic orbitals. What does this mean?
They all have the same energy.
2px orbital
2py orbital
2pz orbitals
Energy of a 2p atomic orbital is ……… than the energy of the 2s atomic orbital
greater than
Two main theories to describe a covalent bond:
Molecular orbital theory
- atomic orbitals are combined to make MO’s.
Valence-bond theory
- electrons within the molecule remain in the atomic orbitals, but we don’t know in which atomic orbital
Addition of wave functions of two atoms leads to…
a bonding molecular orbital
Subtraction of wave functions of the two atoms leads to..
an anti-bonding molecular orbital
anti just means its a higher in energy.
What is a rule of molecular orbital theory?
If you put in 2 molecular orbitals, you must get 2 out.
molecular orbitals for H1…
H2 is made of 2 1s orbitals.
1S a + 1S b
one is anti bonding (higher energy) and the other is a bonding.
Where can the electrons be found in an anti-bonding orbital and in a bonding?
anti bonding - anywhere but the node
bonding - most likely between the nuclei.
In summary
combining two 1s hydrogen atomic orbitals results in…
2 new molecular orbitals with sigma symmetry.
one is anti bonding
the other is bonding
What happens when we combine to 2p atomic orbitals and they bind end on:
sigma anti bonding with 3 nodes
sigma bonding with 2 nodes
2p atomic orbitals can also bind…
side on
pi’ anti-bonding with 2 nodal planes
pi’ bonding with 1 nodal plane
Which is stronger - a pi bond or a stigma pond?
stigma
End on end overlap gives a greater…
overlapping of p atomic orbitals
What is Hybridisation?
where various combinations of orbitals are used to make new hybrid orbitals in order to simplify the maths.
What would we get if we mixed 2s and 2p orbitals together? What does this tell us?
sp3 orbitals
they are degenerate = same energy and same shape.
made up of:
1/4 S and 3/4p
How do the sp3 orbitals arrange themselves?
in a spatial arrangement - to minimise electron repulsion.
gives a bond angle C-H of 109.5 tetrahedral
Shape for the bond angle
180 d
120 d
109.5 d
180 - linear
sp hybridisation
120 - trigonal planar
sp2
109.5 - tetrahedral
sp3
How to know what the hybridisation is?
2 electron groups - sp
3 groups - sp2
4 groups - sp3
double bond counts as one. lone pair counts as one electron group.
All single bonds
are sigma bonds
all double bonds have
one sigma and one pi bond
all triple bonds have
one sigma bond and two pi bonds
Why is hybridisation important?
because it relates to drug structure.
drug structure is controlled by functional groups which s related to valency and hybridisation.
