CHEMICAL BONDING AND MOLECULAR STRUCTURE 7 Flashcards
what is the stability of molecules
If Nb is the number
of electrons occupying bonding orbitals and
Na the number occupying the antibonding
orbitals, then
(i) the molecule is stable if Nb is greater
than Na, and (b/c b.o is +ve)
(ii) the molecule is unstable if Nb is less
than or equal Na.(b/c b.o is -ve or zero)
what is bond order
Bond order (b.o.) is defined as one half the
difference between the number of electrons
present in the bonding and the antibonding
orbitals i.e.,
Bond order (b.o.) = ½ (Nb–Na)
explain nature of bond and bond length
Nature of the bond
Integral bond order values of 1, 2 or 3
correspond to single, double or triple bonds
respectively as studied in the classical
concept.
Bond-length
The bond order between two atoms in a
molecule may be taken as an approximate
measure of the bond length. The bond length
decreases as bond order increases.
how is magnetic nature of molecule determinde dusing mot
Magnetic nature
If all the molecular orbitals in a molecule are
doubly occupied, the substance is diamagnetic
(repelled by magnetic field). However if one or
more molecular orbitals are singly occupied it
is paramagnetic (attracted by magnetic field),
e.g., O2 molecule.
what is distinction of c2 molecule
Diamagnetic
C2 molecules have indeed been detected in It is important to note that
double bond in C2 consists of both pi bonds
because of the presence of four electrons in
two pi molecular orbitals. In most of the other
molecules a double bond is made up of a
sigma bond and a pi bond.
is oxygen diamagnetic or paramagnetic
according to vbt, oxygen should have been diagmagnetic
it contains two unpaired electrons in
π ∗2px
and π ∗2py molecular orbitals, therefore,
O2 molecule should be paramagnetic,
a p r ed i c t ion th a t co r r e spond s to
experimental observation. In this way, the
theory successfully explains the paramagnetic
nature of oxygen.
do li2/c2 molecule extst?
yes in the vapour phase
what are h bonds
Thus, hydrogen bond can be
defined as the attractive force which binds
hydrogen atom of one molecule with the
electronegative atom (F, O or N) of another
molecule.
how are hydrogen bonds formed
When hydrogen is bonded to strongly
electronegative element ‘X’, the electron pair
shared between the two atoms moves far
away from hydrogen atom. As a result the
hydrogen atom becomes highly electropositive
with respect to the other atom ‘X’. Since
there is displacement of electrons towards
X, the hydrogen acquires fractional positive
charge (δ +) while ‘X’ attain fractional negative charge (δ–
). This results in the formation of a
polar molecule having electrostatic force of
attraction which can be represented as:
Hδ+ – Xδ– – – – Hδ+ – Xδ– – – – Hδ+ – Xδ–
what does magnitude of h bonding depend upon
The magnitude of H-bonding depends
on the physical state of the compound. It is
maximum in the solid state and minimum in
the gaseous state. Thus, the hydrogen bonds
have strong influence on the structure and
properties of the compounds
what is intermolecular h bodning
It is
formed between two different molecules of the
same or different compounds. For example, H-bond in case of HF molecule, alcohol or
water molecules, etc.
what is intramolecular h bonding
It is
formed when hydrogen atom is in between
the two highly electronegative (F, O, N)
atoms present within the same molecule. For
example, in o-nitrophenol the hydrogen is in
between the two oxygen atoms.
differentiate bonding and antibonding molecular orbitals
BMO
- formed by additive effect of AO
-e-s placed in bmo results in attraction between the two nuclei
- the e- density is present in between the bonded atoms
-less energy more stable
ABMO
-formed by subtractive effect of AO
-e-s placed in abmo results in repulsion between nuclei
-the e- density is located away from the internuclear region, there is no e- density present in the between the bonded atoms due to presence of nodal plane
-more energy less stable
