CHEMICAL BONDING AND MOLECULAR STRUCTURE 5 Flashcards
explain the attractive and repuslive interactions between the nuclei and electrons
When the two atoms
are at large distance from each other, there
is no interaction between them. As these two
atoms approach each other, new attractive
and repulsive forces begin to operate.
Attractive forces arise between:
(i) nucleus of one atom and its own electron
that is NA – eA and NB– eB.
(ii) nucleus of one atom and electron of
other atom i.e., NA– eB, NB– eA.
Similarly repulsive forces arise between
(i) electrons of two atoms like eA – eB,
(ii) nuclei of two atoms NA – NB.
Attractive forces tend to bring the two
atoms close to each other whereas repulsive
forces tend to push them apart
when are two atoms said to be bonded
the attractive forces are grater than the repuslive forces. Hence the two atoms come close to each other and decrease in potential energy. Consequently the forces of attraction and repulsion balance each other and the molecule attains a state of minimum energy. In this state, it is said to be bonded.
why is molecule more stable than the atom?
Since the energy gets released when the
bond is formed between two hydrogen atoms,
the hydrogen molecule is more stable than
that of isolated hydrogen atoms. The energy
so released is called as bond enthalpy, w
what is overlapping of orbitals/
This
partial merging of atomic orbitals is called
overlapping of atomic orbitals which results in
the pairing of electrons. The extent of overlap
decides the strength of a covalent bond. In
general, greater the overlap the stronger is the
bond formed between two atoms. Therefore,
according to orbital overlap concept, the
formation of a covalent bond between two
atoms results by pairing of electrons present
in the valence shell having opposite spins.
what are the limitations of vsepr theory
-> unable to explain/ predict the shapes of some molecules
-> involves a lot of assumption abt the direction of e- pairs whcih is not clear.
how do two atomic orbitals overlap?
When orbitals of two atoms come close to form
bond, their overlap may be positive, negative
or zero depending upon the sign (phase) and
direction of orientation of amplitude of orbital
wave function in space (Fig. 4.9). Positive and
negative sign on boundary surface diagrams
in the Fig. 4.9 show the sign (phase) of orbital
wave function and are not related to charge.
Orbitals forming bond should have same sign
(phase) and orientation in space. This is called
positive overlap.
define sigma bond
This type of covalent
bond is formed by the end to end (headon) overlap of bonding orbitals along the
internuclear axis. This is called as head
on overlap or axial overlap.
what are the three types of sigma bond
s-s overlapping : In this case, there is
overlap of two half filled s-orbitals along
the internuclear axis
s-p overlapping: This type of overlap
occurs between half filled s-orbitals of one
atom and half filled p-orbitals of another
atom
p–p overlapping : This type of overlap
takes place between half filled p-orbitals
of the two approaching atoms.
define pi bond
In the formation of π bond
the atomic orbitals overlap in such a
way that their axes remain parallel to
each other and perpendicular to the
internuclear axis. The orbitals formed
due to sidewise overlapping consists
of two saucer type charged clouds above and below the plane of the
participating atoms.
describe the stregnth of pi and sigma bonds
Basically the strength of a bond depends
upon the extent of overlapping. In case of
sigma bond, the overlapping of orbitals takes
place to a larger extent. Hence, it is stronger
as compared to the pi bond where the extent
of overlapping occurs to a smaller extent.
Further, it is important to note that in the
formation of multiple bonds between two
atoms of a molecule, pi bond(s) is formed in
addition to a sigma bond.
what is hybridisation
hybridisation which can be defined
as the process of intermixing of the orbitals of
slightly different energies so as to redistribute
their energies, resulting in the formation of
new set of orbitals of equivalent energies and
shape.
what are hybrid orbitals
the atomic orbitals combine to form new set of
equivalent orbitals known as hybrid orbitals.
what are the salinet features of hybridisation
Salient features of hybridisation: The main
features of hybridisation are as under :
1. The number of hybrid orbitals is equal to
the number of the atomic orbitals that get
hybridised.
2. The hybridised orbitals are always
equivalent in energy and shape.
3. The hybrid orbitals are more effective in
forming stable bonds than the pure atomic
orbitals.
4. These hybrid orbitals are directed in
space in some preferred direction to have
minimum repulsion between electron
pairs and thus a stable arrangement.
Therefore, the type of hybridisation
indicates the geometry of the molecules.
what are the important conditions for hybridisation
(i) The orbitals present in the valence shell
of the atom are hybridised.
(ii) The orbitals undergoing hybridisation
should have almost equal energy.
(iii) Promotion of electron is not essential
condition prior to hybridisation.
(iv) It is not necessary that only half filled
orbitals participate in hybridisation.
In some cases, even filled orbitals of
valence shell take part in hybridisation
