Molecular structure/ Photochemistry Flashcards
Why e- promotion?
To equally share the e- at the valence shell to be more stable. Easier to single fill the orbitals than pair up the e-
How to identify the molecular structure arrangement with using the lewis structure
- Count all the valence e-
- Count e- pairs
- Arrange atoms and identify the central atom (the atom that has the lowest ionisation energy)
- Locate bonding pair of e-
- Complete Octets (s2p6) and Duplets (s2 only for hydrogen as it has 1 energy shell only)
- Apply VSEPR theory
Lewis structure gives _______ of molecule
e- arrangement only
what gives the molecular structure/shape
VSEPR Valence Shell Electron Pair Repulsion
Molecule shape alters, depend on__________
VSEPR theory
AX(2)E(1)
sp^2 (2 bonding pair e-, 1 lone pair e-) – Bent
AX(6)
sp^3d^2 (6 bonding pair e- ) – Octahedral
e.g. SF(6)
AX(5)
sp^3d (5 bonding pair e-) - Trigonal bipyramidal
AX(4)
sp^3 (4 bonding pair e-) – Tetrahedral
AX(3)
sp^2 ( 2 bonding pair e-) - Trigonal planar
AX(2)
sp (1 bonding pair e-) – linear
List different types of structure arrangement
AXn ; AX(n-1)E(1) ; AX(n-2)E(2)
A- Central atom
X- Bonding e- pair
E- Lone e- pair
Hybridsation happens because ___________
valence e- get promotion and energy re- arranged in order for the atom to become more stable.
(2s & 2p energy difference is small, doesn’t take much for energy re-arrangement take place)
When Hybridsation has to happen ?
Before molecular bonding. It is the overlap of two different energy valence orbitals of the same atom e.g. orbital s – p
If 2 e- of Carbon hybridise, it gives ?
it will give sp + 2p > 1 sigma, 2 pi bond > which gives the atom a triple bond i.e., alkyne
If 3 e- of Carbon hybridise, it gives?
it will give sp2 + 1p > 1 sigma, 1 pi bond > which gives the atom a double bond i.e., alkene
If 4 e- of Carbon hybridise, it gives?
it will gives sp3 > a sigma bond > which gives the atom single bond i.e., alkane
Intranuclear distance
The distance between two nuclei in a molecule = Σ(a) - Σ(r)
Quantum
energy amount balancing out the energy level
Energy __________ when bond break
Energy __________ when bond formed
- Needed
- Released
What affects the bond length and bond strength
- No of p+
- No of e-
- No of energy shell
- Atomic radius
- No of shared e-
The greater the bonding energy, the _________bond strength, the more_______the molecule is
the stronger bond strength; the more stable stable the molecule is
Anti- bonding orbitals has _________ energy than bonding orbitals
more energy
Homonuclear molecule
molecules composed of one type of element
Degenerate orbitals
Orbitals with the same energy level
E.g. p orbital > px / py / pz
How many e - on each orbitals
2 e-
how many e- on each sub level
s -2
p - 6
d - 10
f - 14
how many e- on each sub shell
1st - 2
2nd - 8
3rd - 18
4th - 32
why He(2) doesn’t exist?
because he already has a full outer shell, it doesn’t need boning to become stable
The bonding orbital energy level sequence depends on the ___________
element combination
HOMO/ LUMO theory
The energy difference between Highest Occupied Molecular Orbitals & Lowest Unoccupied Molecular Orbitals
π bonding energy is always greater than σ bonding, because__________
π bonding is p - p (side - side) orbitals overlap
σ bonding is s- s / s-p / p-p (head - head) orbitals overlap
lone pair e- has more energy than bonding pair e- , because_______
bonding pair e- are fixed ; lone pair e- are free to spin around
Based on the HOMO/LUMO theory, e- transition can be ? and what is needed for the transition ?
σ - σ * π - π * n - π n - σ * Energy
Bond length
Distance between the 2 nucleus as a stable structure and bond formed
Rules for bonding orbitals
No of combining atomic orbitals = no of molecular orbitals
But may not be the same type of orbitals
Hybridisation is based on ____
- electronic configuration
- Octet rule
- Ability of non- metal
- Share e- to obey the Octet rule
Sigma bond
Pi bond
- Overlap of orbitals s – s / s- p / p – p, head to head gives sigma bond
- Overlap of orbitals p – p, side to side gives pi bond.
Lewis acid
Lone pair acceptor e.g. BF(3)
Hybridisation gives ___________
~ re-arrangement e-
~ mixing of orbitals
~ mixing of properties
Hybrid bond is
an atomic bond
Hybrid orbital is
an atomic orbital
Evidence of hybridisation
The molecular shape
The molecular shape has impact on
molecular behaviours
Lewis base
lone pair donor e.g. NH(3)
For complex chemistry, Ligand will ________ lone pair e- ; Transmetal will ________ lone pair e-
- donate
- accept
Complex chemistry
small molecules stick together to form complex molecule
Complex bond
Use of Lewis Acid/ Base come together to give dative bond
hierarchy of repulsion of e-
Non- bonding e- Non- bonding e-
bonding e- Non- bonding e-
bonding e- bonding e-
What can also act as Ligands
Polyatomic ions and simple ions
monodentate ligand
one pair of e- donated
polydentate ligand
more than one pair of e- donated
Alloy
- mixture composed of different metal elements
- e.g. Steel > iron and some other metal
- allowed because of similar atomic radius of d elements
Magnetism of d element
Fully magnetic - iron / nickle/ cobalt
Partial magnetic
Dimagnetic
Polyatomic cation & simple cation that have
the same charge will behave __________
Polyatomic cation & simple cation that have the different charges will behave __________
- behave the same when in solution
- behave different yet similar in the solutionW
Wavelength = energy
Shorter the λ, _____ the energy ; longer λ, ________ the energy
Shorter > higher E
Longer > lower E
Refer to the e- transition, increase in internal energy = ?
Decrease in internal energy = ?
increase = absorption decrease = Emission
If it is white, ?
If it’s dark, ?
No interaction if it’s white, all light bounce back
If it’s dark, light is absorbed
e- transition
~ e- energy jumping from low energy orbital to high energy orbital
~ splitting of energy at d- orbital
~ d orbital normal degenerate
Crest
Trough
amplitude
Wavelength
- top of the curve
- bottom of the curve
- line the tip of curve
- distance between a crest and the next / a trough to the next
Different wavelength
Cosmic rays > Gamma rays > X rays (bonds of all 3 will break because of the high energy)
> ultraviolet >Visible > infrared > Microwave > Radio
Visible spectrum
400 nm - Violet > Blue > Green > Yellow > Orange > Red > Purple - 800nm
Within the electric field, how will electron behaves?
- Bond breaking & ionisation (X rays)
- Electronic excitation (Visible & ultraviolet)
- Vibration (infrared)
- Rotation (microwave)
Self sustaining free radical cycle: 3 steps ?
~ Initiation – photodissociation / photolysis
~ Propagation
~ Termination
Summary of the important reactions for formation of Smog
NO2 absorbed solar energy > NO + O
- -> NO reacts with O3 > NO2+
- -> NO2 react further with hydrocarbon free radicals > PAN, aldehydes and other smog components
- -> O reacts with O2 yield Ozone molecule, O3
- –> O3 + OH+ > highly reactive hydrocarbon free radicals
OH+ reacts with other species > chain reactions
polyatomic ions
- ions that contains more than one type of elements - Resonance structure - All atoms covalent bonded - Delocalisation of charge
Photochemistry
Energy taken in and transfer e- to higher energy. Energy given up as light and the lowering of energy
(Excess energy is get rid of by releasing light)
Light
Electromagnetic radiation , energy travelling in waves
All light travels in ___________, different types of light has ____________
travels in a fix pattern
has a specific wave length
Speed of light formula / Energy of wave length formula
1) C = v. λ
2) E= h. v
–> E α 1/ λ
[C= speed of light v = frequency λ = wavelength E = energy h= Plank’s Constant]
longer λ more likely to ________
be bounced off and scatter
What would affects the colour change
pH changes / e - rearrangement / changing the bonding between / electronic structure change / energy absorbed change
Octet rules are not always followed, why?
Full filled valence shell & 1/2 filled valence shell are most stable
For example most d elements can lose variable no of e- (Oxidation state) Most possibly happen in the middle of d- block, and decrease as go towards s/ p block
Oxidation state
most d elements can lose variable no of e- to achieve full valence shell or half full valence shell to be more stable.
D orbital electrons
dz2 dx2-y2 dxy dyz dxz
D orbital splitting
dz2 dx2-y2
| (Octahedral)
dxy dyz dxz
dxy dyz dxz
| (Tetahedral)
dz2 dx2-y2
D block element (Trans metal)
- Lattice structure
- Alloy
- Magnetic properties
- Redox chemistry
- Ability of the same element to form different colour solutions < orbitals can be split ; Light can come in as energy to promote e-
- Ligand: something that bind with metals
Co- ordinate ions
a form of polyatomic ions with d- block metal in the central with a ligand bond to it with a covalent bond
Example of a natural molecule to become ligand
Water
Free radical
It is with un- paired e- ; extremely reactive and seek to pair up e-
Covalent bonds from the free radical are break & reformed
It is related to cancer and antioxidant interaction
