CHEMICAL BONDING AND MOLECULAR STRUCTURE 3 Flashcards
what is resonance
Used for polyatomic species
* Delocalisation of p-electron
* To explain stability of species
who introduced MOT
MOT put forward by Hund & Mulliken, which can be applied to explain the properties, which the old VBT
(Valence bond theory) was unable to explain. eg. Paramagnetic nature of O2
molecule, as per VBT (:O = O:)
it should be diamagnetic.
what is the molecular orbital theory
The atomic orbital lose their identity during molecule formation (overlapping) and form new
orbitals termed as molecular orbitals.
what is are the 2 molecular orbitals
Half of the molecular orbital have lower energy are called Bonding molecular orbital. (BMO)
(d) Half are of higher energy - termed as Antibonding molecular orbital. (ABMO)
differentiate bonding and antibonding molecular orbital
BMO
(i) Bonding molecular orbital is formed due to the addition or constructive interference of the two atomic orbitals
yb = yA + yB
(ii) It has lower energy more stable
(iii) doesnt have nodal planes
(iv)Electron density increases between two nuclei
resulting attraction between two atoms.
(v)Electron placed in a BMO stablises a molecule.
ABMO
(i) formed due the subtraction of destrcutive interference of the two atomic orbitals
(ii) It has higher energy less stable
(iii) Has nodal planes It always have a nodal plane between two nuclei
of bonded atom.
iv)Electron density decreases in between two
nuclei, leads to repulsion between two atoms.
vElectron placed in the ABMO destablises
the molecule.
what are the applications of mot
(1) Stability of molecule
If molecule has ‘0’ bond order then molecule will not exist.
If Nb>Na, then it is stable
If Nb=Na or Nb<Na, the molecule do not exist
Stability µ bond order.
(2) Magnetic property
(a) When electron in MO are paired — diamagnetic
(b) When electron in MO are unpaired — paramagnetic
(3)
If bond order is fractional then molecule will be paramagnetic.
Why is H2+ more stable than H2-
H2- is less stbale because it conatins 1 e- in antibonding orbital
what is h bonding
It is not formed in ionic compounds.
(c) H–bond forms in polar covalent compounds, (not in non-polar).
(d) It is very weak bond but stronger than vander waal’s force.
(e) It is also known as dipole-dipole attraction.
Why is there hydrogen bonding in HCN
Due to cn triple bond,with sp hybridisation and electronegativity of carbon and nitrogen.
Why is there strong bonding in water and HF
In water molecule one molecule of water is bonded with 4 other.
In HF molecule, there is bonding due high electronegativoty of fluorine.
explain intramolecular bonds
H–bonded with electronegative element of a functional group, form H–bond with another electronegative
element present on nearest position on the same molecule.
(b) This type of H–bond is mostly occurred in organic compounds.
(c) It results in ring formation (Chelation).
strength is lesser than intermolecular bonds
ex:
o-nitrophenol
salicylaldehyde
chloral hydrate
o-flourophenol
solubility and h bondinh
the molecules which have intermolecular h bonding are soluble. but those which have intramolecular are less soluble as hydrogens are not necessary fo rbondng
mpt and bpti
due to intermolecular h bonding, mpt and bpt of cpds increase. but due to intramolecular h bonding so the force of attraction among these molecules
are vander waal force. So M.P. and B.P. are low.
what is molecular weight
molecular weight of acetic acid is double its molecular formula due to dimer formation
what are van derwaal forces
These are weak; non directional, non valence force of attraction among neutral species.
(b) These are electrical in nature, due to induced polarity caused by temporary displacement of electrons
towards one end of the inert atoms, becoming a temporary dipole.
d+ d-
