Structure of Atom 7 Flashcards
state aufbau’s principle
In the ground state of the
atoms, the orbitals are filled in order of
their increasing energies. In other words,
electrons first occupy the lowest energy orbital
available to them and enter into higher energy
orbitals only after the lower energy orbitals
are filled. As you have learnt above, energy
of a given orbital depends upon effective
nuclear charge and different type of orbitals
are affected to different extent. Thus, there
is no single ordering of energies of orbitals
which will be universally correct for all atoms.
explain aufbau principle
In other words,
electrons first occupy the lowest energy orbital
available to them and enter into higher energy
orbitals only after the lower energy orbitals
are filled. As you have learnt above, energy
of a given orbital depends upon effective
nuclear charge and different type of orbitals
are affected to different extent. Thus, there
is no single ordering of energies of orbitals
which will be universally correct for all atoms.
state pauli’s exclusion principle
According to this principle : No two
electrons in an atom can have the same set
of four quantum numbers. Pauli exclusion
principle can also be stated as : “Only two
electrons may exist in the same orbital and
these electrons must have opposite spin.”
explain pauli exclusion principle
This means that the two electrons can have
the same value of three quantum numbers
n, l and ml
, but must have the opposite spin
quantum number. The restriction imposed
by Pauli’s exclusion principle on the number
of electrons in an orbital helps in calculating
the capacity of electrons to be present in any
subshell.
the maximum number
of electrons in the shell with principal
quantum number n is equal to 2n2.
why is it called pauli’s exclusion principle
In an atom, the electron in an orbital has specific values for n, l and ml and s then all other electrons in the atom are excluded from having the same same set of values for the 4 quantum
what is hund’s rule of maximum multiplicitiy
In a given subshell, the pairing of electrons in orbitals of tht subchell does not take place until each orbital in that subshell has got atleast one eelctron, ie it is singly occupied.
why is hund’s rule followe d
Since there are three p, five d and seven f
orbitals, therefore, the pairing of electrons will
start in the p, d and f orbitals with the entry
of 4th, 6th and 8th electron, respectively. It
has been observed that half filled and fully
filled degenerate set of orbitals acquire extra
stability due to their symmetry
what is electronic configuration
it is the distrubution of electrons in the orbitals, subshells and shells of an atom
why is it called maximum multiplicit rule
means that the total spin of unpaired e-s is maximum
what is the utility of knowing
the electron configuration?
The modern
approach to the chemistry, infact, depends
almost entirely on electronic distribution to
understand and explain chemical behaviour.
For example, questions like why two or more
atoms combine to form molecules, why some
elements are metals while others are nonmetals, why elements like helium and argon
are not reactive but elements like the halogens
are reactive, find simple explanation from the
electronic configuration. These questions have
no answer in the Daltonian model of atom.
A detailed understanding of the electronic
structure of atom is, therefore, very essential
for getting an insight into the various aspects
of modern chemical knowledge.
wht is the stability of half filled and fully filled electrons
The ground state electronic configuration of
the atom of an element always corresponds to
the state of the lowest total electronic energy.
The electronic configurations of most of the
atoms follow the basic rules given in Section
2.6.5. However, in certain elements such as
Cu, or Cr, where the two subshells (4s and
3d) differ slightly in their energies, an electron
shifts from a subshell of lower energy (4s) to a
subshell of higher energy (3d), provided such
a shift results in all orbitals of the subshell
of higher energy getting either completely
filled or half filled.
what is the symmetrical distrubutuion of electron
It is well known that symmetry
leads to stability. The completely filled
or half filled subshells have symmetrical
distribution of electrons in them and
are therefore more stable. Electrons in
the same subshell (here 3d) have equal
energy but different spatial distribution.
Consequently, their shielding of oneanother is relatively small and the
electrons are more strongly attracted by
the nucleus.
what is the exhange energy
The stabilizing
effect arises whenever two or more
electrons with the same spin are present
in the degenerate orbitals of a subshell.
These electrons tend to exchange their
positions and the energy released due to
this exchange is called exchange energy.
The number of exchanges that can take
place is maximum when the subshell
is either half filled or completely filled
(Fig. 2.18). As a result the exchange
energy is maximum and so is the stability.
what are the reasons due to the extra stability and half filled or ocmpletely filled e-s
i) relatively small shielding
ii) smaller couloumbic repulsion
iii) larger exchange energy
