Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out

orbital

VIEWS: 110 PAGES: 8

									Bangladesh Collage of
 Leather Technology

               Assignment
                   On

         Inorganic chemistry



             Submitted to
               Md. Halim
           Dept. of chemistry
Bangladesh Collage of Leather Technology




                Submitted by

         Md. Mohiuddin Alamgir
              Class id-27028
               Batch id-27th
        Dept. of leather technology


                     1
Orbit:
        An orbital as definite circular path at a definite distance round the nucleus where
electrons are revolving without radiating any energy. For example, according to Bohr’s
theory, an electron of hydrogen is found at distance of 0.53A◦ from the nucleus.

Orbital: It is defined as
                       The three dimensional region or space around the nucleus of an
atom where there is maximum probability of finding an electron having certain energy is
called atomic orbital

Types of orbital:
                   There are four types of orbital. They are

                                                 1.   s- orbital or s sub-shell
                                                 2.   p- orbital or p sub-shell
                                                 3.   d- orbital or d sub-shell
                                                 4.   f – orbital or f sub-shell


s sub-shell:
              s sub-shell which is present in all the energy levels contains only one orbital
called s-orbital. Every s-orbital is spherically symmetrical. s-orbital of any energy level
has only one orientation and hence called can be arranged in space only in one way along
x, y or z axis. The 1s orbital is everywhere positive. Beginning with 2s, there are
alternating positive and negative region.




                                     Fig: s-orbital

p-sub shell:
           p sub-shell which starts from 2nd energy level (L-shell). For this sub-shell l=1.
Now when l=1 then m=-1,0,+1 (three values).three values of m(=-1,0,+1)for l(p sub-
shell)imply that p sub-shell of any energy level has three space orientations and hence
can be arranged in space in three different ways along to x, y and z axes. So there are
three orbital in each set, one along the x axis px, one along the y axis py, one along the z
axis pz. Each p-orbital consists of positive lobe along the positive extension of a cartesian
axis and a negative lobe along the negative extension of the same axis.
         p-orbitals are dumb-bell in shape. The 2p orbital have no radial nodes, but
beginning with 3p orbital node as well. In the absence of magnetic field, all the three p-
orbital have the same energy.


                                             2
 Fig:px-orbital                   Fig: pz-orbital                    Fig: py –orbital




d sub-shell:
              d sub-shell which starts from 3rd energy level(M-shell).For this sub-shell
l=2.Now when l=2, then m=-2,-1,0,+1,+2. Five values of m imply that d sub-shell of any
energy level has five space orientations and hence can be arranged in space in five
different ways along x, y and z axes. So each set of d-orbital consists of five members.
The important features of d-orbital are
                     1. The dz2 orbital is symmetrical in shape about the z axis.
                      2. The dxy, dyz, dzx orbital are exactly alike except that they have
their maximal amplitudes in the xy, yz and zx planes respectively.
                      3. The dx2-y2 orbital has exactly the same shape as the dxy orbital, but
it is rotated by 45◦ about the z axis, so that its lobes are directed along the x and y axis.




Fig: dxz-orbital       Fig: dx2-y2 orbital        Fig: dzx-orbital     Fig: dxy-orbital




                                       Fig:dz2-orbital


f sub- shell:
           f sub-shell which starts from 4th energy level(N-shell). For this sub-shell l=3.
Now when l=3, then m=-3, -2, -1, 0, +1, +2, +3(seven values). Since m has seven values
for l=3 value, f sub-shell has seven space orientations and hence can be arranged in space
in seven different ways along x, y and z axes. The 4f orbital play only a slight role in


                                              3
chemical bonding. But the 5f orbital are extensively employed in bonding in various
compounds formed by the actinide elements.




                                  Fig: f-orbital

Orbital diagram:
                   We use a diagram to show how the orbitals of a sub-shell are
occupied by electrons. It is called an orbital diagram. An orbital is represented by
a circle. Each group of orbital in a sub-shell is labeled by its sub-shell notation. An
electron is an orbital is shown by an arrow; the arrow points up when ms=+½and
down when ms=-½. The orbital diagram of B(5) is

              ↑↓      ↑↓      ↑
              1s      2s          2p


   Difference between Orbit and Orbital:
                                       The points of difference between an orbit and an
orbital are given below


                   Orbit                                    Orbital
     1. As postulated by Bohr, an orbit is      1. The three dimensional region or
a definite circular path at a definite space around the nucleus of an atom
distance from the nucleus in which the where there is maximum probability of
electron revolves round the nucleus.       finding an electron having certain energy
                                           is called atomic orbital.

     2. An orbit indicates exact position     2. An orbital does not specify the
or location of an electron in an atom.    definite or exact position of an electron
                                          in an atom.
     3. There is a certainty about the        3. Due to uncertainty principle, there
movement of an electron in an orbit.      is no certainty about the movement of an
                                          electron in an orbital.


     4. It represents the planar motion of    4. It represents the three- dimensional
the electron.                              motion of the electron round the nucleus.



                                             4
      5. The maximum number of                    5. An orbital cannot accommodate
electrons in an orbit is equal to 2n2, where more than two electrons.
n is the number of the orbit.
      6. Orbits are circular in shape.            6. Orbital have different shapes, e.g
                                             s- orbital is spherically symmetrical.

Quantum number:
                   These are the integral number which describe the energy of an electron
in an orbit, the position(distance) of the electron from the nucleus ( radius of the orbit),
shape and number of orientation of an electron cloud (orbital) round its own axis and the
direction of the spinning of the electron round its own axis.
        There are four numbers which are
                                           1. Principal quantum number (n)
                                           2. Azimuthal quantum number (l)
                                           3. magnetic quantum number (m)
                                           4. spin quantum number (s)


1. Principal quantum number (n):
                                        It is the radial distribution quantum number and
determining the energy corresponding to an orbital. It indicates the size of an energy
level. It also gives the radial distance from the nucleus. It is restricted to take on the
integral values 1, 2, 3…………..etc. Each principal quantum number corresponds to a
main energy level or shell. The first shell nearest to the nucleus has n=1 and is designed
as k shell, similarly n=2, 3, 4……… etc corresponds to L, M, N……. etc respectively.

2. Azimuthal quantum number (l):
                                            Azimuthal   quantum      number       determines
magnitude of the orbital angular momentum and hence is also called orbital angular
momentum quantum number. The angular momentum quantum number (l) indicates the
shape of the orbital. The values of l depend on the values of the principal quantum
number n. For a given value of n, l has possible integral values from 0 to (n-1).
               If n=1 then l= (n-1) =1-1=0. If n=2 there are two values of l given by 0
and 1. If n=3 then, l=0, 1 and 2. If n=4 then l=0, 1, 2 and 3. The four values of l are
generally designed by the letters s, p, d, f……… as follows
n=1            l=0             s sub-shell
n=2            l=0, 1          p sub-shell
n=3            l=0, 1, 2       d sub-shell
n=4            l=0, 1, 2, 3    f sub-shell
…………………………………................so on.

3. The magnetic quantum number (m):
                                             The magnetic quantum number describes
the orientation of the orbital in space. With a sub-shell the value of m depends on the
angular momentum number l. For a certain of l, there are (2n+1) integral values of m as
follows


                                             5
        -l, (-l+1)…….0……... (+l-1), +l
                                      If l=0, then m=0. If l=1 then, there are three values
of m namely -1, 0 and 1. The numbers of m values indicate the number of orbital in a
sub-shell with a particular l values.

4. Spin quantum number (s):
                                  The Spin quantum number is introduced to account for
the spin (clockwise or anticlockwise) of the electron such a spin would contribute to the
angular momentum of the electron. This spin is also quantized, there are only two
possible values which spin quantum number (s) may have, s=  ½ according to whether
the electron spins clockwise or anticlockwise.


Heisenberg uncertainty principle:
                                        In 1927 Wrner Hesenberg showed from quantum
mechanics that“it is impossible to measure simultaneously the exact position and exact
momentum of a sub-atomic particle like an electron and neutron”.
    Heisenberg’s uncertainty principle is a relation that states the product of the
uncertainty in position and the uncertainty the momentum of a particle can be no smaller
than plank’s constant divided by 4π.
        Thus letting Δx be the uncertainty in the x co-ordinate of the particle and letting
Δpx be the uncertainty in the momentum in the X direction, we have

                                             h
                              (Δx)(Δpx)≥
                                            4
There are similar relations in the Y and Z direction.
       The uncertainty principle says that the more precisely we know the position, the
less well we know the momentum of the particle.


Pauli’s Exclusion Principle: Pauli’s exclusion principle stales that
                                                                      It is impossible for
two electron residing in the same orbital of a given poly-electron atom to have same
values of all the four quantum number.
              Let us consider an atom has two electrons according to Pauli Exclusion
Principle it true quantum number are same but the fourth must be different.
For first electron n=1, l=0, m=0, s=+½
For second electron n=1, l=0, m=0, s=-½


Aufbau Principle:
                     Aufbau is a German expression which means building up or
construction.
                    The Aufbau principle (building up principle) is a scheme used to
reproduce the electron configuration of the ground states of atom by successively filling



                                            6
sub-sell with electrons in a specific order. The orbital of minimum energy are filled first
with electrons and then the orbital of the higher energy start to fill.
     The energy of an orbital depends on the quantum numbers n and l. If the value of
(n+l) for an orbital is higher the energy of the orbital is higher.

    If the values of (n+l) are the same, the energy of the orbital is lower whose n is
minimum. Thus we obtain the electronic configuration of an atom in the following order:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f. . . . . . . . . .


Hund’s rule: It stats that,
                          The lowest energy arrangement of electron in a sub-sell is
obtained by putting electron in to separate orbital of the sub-sell with the same spin
before pairing electrons.
                                               1s2     2s2    2p3
    e.g.The electronic configuration of N(7)→ ↑↓       ↑↓     ↑↑↑


Electron spin:
                 Otto stern and Walther Gerlach first observed electron spin magnetism in
1921. They directed a beam of silver atoms into the field of a specially designed magnet.
The same experiment can be done with hydrogen atoms. The beam of hydrogen atoms is
split into two by the magnetic field; half of the atoms are bent in one direction and half in
the other.
                       The beam of hydrogen atom is split into two because the electron
in each atom behaves as a tiny magnet with only two possible orientations. In effect, the
electron acts as though it were a ball of spinning charge and like a circulating electronic
charge the electron would create a magnetic field. Electrons spin, however, a subjected to
a quantum restriction on the possible directions of the spin axis. The resulting directions
of spin magnetism corresponding to spin quantum numbers ms=+½ and ms=-½

                              S                                    S



                  ↑ ↑↑                                  ↑ ↓↑
                                          Direction
                                         of external
                                            field

                         ms=+½                                 ms=-½
                           N                                      N

                  External magnet                           External magnet

                                    Fig: A representation of electron spin.




                                             7
Spectrum; It is defined as
                              A spectrum is an array of waves or particles which is spread
out according to the increasing or decreasing of some such as wavelength or frequency.

Types of Spectrum;
                       Depending on the nature of the source emitting the radiation, there
are two types of spectra.
           1. Emission spectra
           2. Absorption spectra
           Emission spectra are further of two types:
           a. Continuous spectrum
           b. Discontinuous spectrum which may be bond spectrum or line spectrum.
               Line spectrum is also called atomic spectrum.


                                      Spectra



                Emission spectrum                                 Absorption spectrum


  Continuous spectrum                       Line spectrum

Continuous spectrum:
                       When a beam of white light is passed through a prism different
wavelengths are refracted through different angle. When received on a screen, these form
a continuous series of colour bands; violet, indigo, blue green, yellow, orange and red
(VIBGYOR).This series of bands that form a continuous rainbow of colours is called
continuous spectrum.


Line spectrum:
                 A spectrum showing only certain color or specific wavelengths of light
when an electric discharge is passed through hydrogen gas, the molecules of the
hydrogen breaks into atoms. These atoms absorb energy from electric spark and get
excited. The excited atoms give the extra energy to form emitted light. When this emitted
is allowed to pass through a prism line spectrum of H-atom is obtain. This spectrum is
called line emission spectrum.




                                            8

								
To top