CHEMICAL BONDING AND MOLECULAR STRUCTURE 4 Flashcards
what is dipole
the molecule
possesses the dipole moment (depicted
below) which can be defined as the product of
the magnitude of the charge and the distance
between the centres of positive and negative
charge. It is usually designated by a Greek
letter ‘µ’
formula of dipole moment
Dipole moment is usually expressed in
Debye units (D). The conversion factor is
1 D = 3.33564 × 10–30 C m
where C is coulomb and m is meter.
what is the direction of dipole moment
This arrow symbolises the direction of the
shift of electron density in the molecule.
how is dipole moment dependent on spatial arrangement of molecules
In case of polyatomic molecules the dipole
moment not only depend upon the individual
dipole moments of bonds known as bond
dipoles but also on the spatial arrangement
of various bonds in the molecule. In such
case, the dipole moment of a molecule is the
vector sum of the dipole moments of various
bonds.
dipole moment of bf2 is 0. explain2
The dipole moment in case of BeF2 is zero.
This is because the two equal bond dipoles
point in opposite directions and cancel the
effect of each other.
what is dipole moment in bef3. xplain
In tetra-atomic molecule, for example in
BF3, the dipole moment is zero although the
B – F bonds are oriented at an angle of 120o
to one another, the three bond moments give
a net sum of zero as the resultant of any two
is equal and opposite to the third.
Although fluorine is more
electronegative than nitrogen, the resultant dipole moment of NH3 (4.90 × 10–30 C m) is
greater than that of NF3 (0.8 × 10–30 C m). why
This
is because, in case of NH3 the orbital dipole
due to lone pair is in the same direction as
the resultant dipole moment of the N – H
bonds, whereas in NF3 the orbital dipole is in
the direction opposite to the resultant dipole
moment of the three N–F bonds. The orbital
dipole because of lone pair decreases the effect
of the resultant N – F bond moments, which
results in the low dipole moment of NF3.
what is the vsepr theory
The VSEPR Theory states that the electron pairs present in bonds and lone pairs repel each other and thus adpt a geometry that places the electron pairs as far away as posisibe
what are the postulates of vsepr theory
- The shape of a molecule depends upon
the number of valence shell electron pairs
(bonded or nonbonded) around the central
atom. - Pairs of electrons in the valence shell repel
one another since their electron clouds are
negatively charged. - These pairs of electrons tend to occupy
such positions in space that minimise
repulsion and thus maximise distance
between them. - The valence shell is taken as a sphere
with the electron pairs localising on the
spherical surface at maximum distance
from one another. - A multiple bond is treated as if it is a single
electron pair and the two or three electron
pairs of a multiple bond are treated as a
single super pair. - Where two or more resonance structures
can represent a molecule, the VSEPR
model is applicable to any such structure.
what the repusilve interatin descreasing order
lp-lp> lp-bp> bp-bp
why is lp lp repulsionmore than bplp repuslion
explaining the important
difference between the lone pairs and bonding
pairs of electrons. While the lone pairs are
localised on the central atom, each bonded
pair is shared between two atoms. As a result,
the lone pair electrons in a molecule occupy
more space as compared to the bonding pairs
of electrons. This results in greater repulsion
between lone pairs of electrons as compared
to the lone pair - bond pair and bond pair -
bond pair repulsions
why does water have bent shape
The shape should have been
tetrahedral if there were all bp
but two lp are present so the
shape is distorted tetrahedral
or angular. The reason is
lp-lp repulsion is more than
lp-bp repulsion which is more
than bp-bp repulsion. Thus,
the angle is reduced to 104.5°
from 109.5°.
why does so2 ozone and so3 have bent shape
Theoretically the shape
should have been triangular
planar but actually it is found
to be bent or v-shaped. The
reason being the lone pairbond pair repulsion is much
more as compared to the bond
pair-bond pair repulsion. So
the angle is reduced to 119.5°
from 120°.
the bond anbgle of nh3 i reduced why
Had there been a bp in place
of lp the shape would have
been tetrahedral but one
lone pair is present and due
to the repulsion between
lp-bp (which is more than
bp-bp repulsion) the angle
between bond pairs is
reduced to 107° from 109.5°.
why is the bond angle of sf4
In (a) the lp is present at axial
position so there are three
lp—bp repulsions at 90°.
In(b) the lp is in an equatorial
position, and there are two
lp—bp repulsions. Hence,
arrangement (b) is more
stable. The shape shown in
(b) is described as a distorted
tetrahedron, a folded square
or a see-saw
