Shape of orbitals....

According to wave mechanical concept  " The maximum probability of the existence of the electron is at a given distance from the nucleus " .  According to Bohr's calculation and according to wave mechanics the value of that distance have same value.

Wave mechanics  says that  "The space  around  the nucleus where probability of finding of electron is very high " is called  atomic orbitals.

1. Shape of S- orbitals--
              
--For S-orbitals  l = 0 therefore m = 0 but the value of  n  can vary.
 --All the s orbitals has spherical  shape , maximum electron find in this region.
 -- S orbitals can hold maximum 2 electrons, each with opposite spin.

1.                                                                                                               

                                                                                                                        

2. Shape of P- orbitals -

            

 -  All  orbitals  have l (Azimuthal q. number) = 1 and 3 possible values of m (-1 , 0, +1)

 -All the p orbitals (Px, Py, Pz)  are dumbell shape ,the region where the probability of finding of electron is very high.

3. Shapes of d- orbitals-

  -There are total 5 possible values for orbitals

dz2,

dxz

,dyz

,  dxy

,    dx2−y2

-Above picture shows that first four d-orbital are double dumbell shape while last dz orbital is dumble shape with a collar in xy plane.It means maximum electron can be find in that given orientation or in that planes.

-For d orbitals n = 3 onwards.
   maximum numbers of electron in d- orbitals = 10 .

4. Shape of f- orbitals-
 - Shape of f orbitals are very complex then  d- orbitals ..
-There are total 7 f- orbitals .

-Maximum number of electron found in f - orbitals = 14.

Place of  s, p, d, f  orbitals in periodic table--

Filling of electron in s, p, d, f orbitals follow the given order--

      1s->2s->2p-> 3s-> 3p-> 4s-> 3d-> 4p.....so on

Energy of orbitals in increase in following order--

      1s< 2s<2p< 3s< 3p< 4s <3d< 4p ...





=> Value of energy and radius of orbitals increases with increase in number of orbitals  or  with increase in  Principal quantum number  n (shell).l

8. Quantum numbers..

We know that any atom is composed of many shells named  K, L, M, N..etc. All the shells contains subshells i.e. s, p, d, f, ...etc, and each subshell composed of various orbitals..i.e. 

S, px , py , pz

dz2,

dxz

,dyz

,dxy

,dx2−y2

--Simply this is a  process of naming of these shells, subshells ,  orbitals and their spin orientation by a numbers and these numbers are called Quantum number.
-- It is found by the solution of Schrodinger wave equation for hydrogen atom.

There are four types of Quantum number

1. principal q.no. (n)-  which reprasent main energy level or shells in which the electron is present.        
                    n= 1, 2, 3, 4, ....
2. Orbital angular momentum quantum number or Azimuthal  q. no. (l)- It described the orbital motion of the electron around the nucleus which is described by the orbital angular momentum of the electron.thus it is called orbital angular momentum quantum number.     
                                 l = n-1
 3. magnetic q. no.  (m)- Since the magnetic or electrical field generated by the angular momentum of the electron interact with external magnetic or electric field.The electron orient or revolve themselves in a specific regions of space around the nucleus called orbitals.The number of  orbitals in a given sub energy level (l) within a principal energy level (n) is given by the number represented by m ,called magnetic quantum number.
Possible values of m is
                                     m = 2l +1
  
4. Spin q. no.  (s)-- It arises by the spnning of electron around the nucleus as well as around its own axis. We will discuss it below. 
    

Shells	K, L, M, N..	Represented as   n
Subshells	S, p, d, f…	Represented as   l
Orbitals	S, px , py , pz dz2, dxz   ,dyz ,dxy ,dx2−y2 ,fz3 ,fxz2 ,fyz2 ,fxyz ,fz(x2−y2) ,fx(x2−3y2) ,fy(3x2−y2. …	Represented as  m
Spin	Up  or Down	Represented as  s

Example:-- for electronic configuration  given below  the value of n , l, and no. of electron  is 1, 0, 2 respectively.
    

--Possible values for n, l, m, s                             

n	1, 2, 3, 4…
l	0 to n-1
m	+ ι , 0, - ι
S	+1/2, or   -1/2

-- Quantum number presents the position of electron and it also indicates the distance of electron from the nucleus..
If n = 1
    l = 0   
then the position of electron = 1s
If  n = 2
    l = 1
then position of electron = 2p
 If  n =3
    l = 2
then position of electron = 3d
-- Picture given below shows the distance of orbitals from nucleus and the energy as well..                                     

 --If we know the principal quantum number we can determine the radius , velocity , and energy of the electron .

Spin quantum number-
                      Fourth q. no. doesn't follow from wave mechanical treatment. It arises from the spectral evidence that electron in its motion around the nucleus also rotates or spin about its own axis. Because of this rotation the electron has magnetic moment called spin magnetic moment which can be either up or down spin .
    
-Spin angular momentum is characterised by a Q . number S
                       S = 1/2,   either +1/2 or -1/2.
 Hydrogen spectra fine structure is observed as a doublet corresponding to two possibilities for the Z-component of the angular momentum , where for  any given direction Z the value of Spin  angular momentum S is ..
                   

                                               Sz =   ± 1/2 ћ

--Its solution give to possible  Z- component for electron  spin up and spin down

--When atom have even no. of electron in each orbitals , orientation of one electron will be opposite to other , or each electron will be opposite in orientation to that of its immediate neighbour.

-In the early year of Quantum mechanics atomic spectra external field can't be predicted with just n, l, m.

-Unlenbeck , Goudsmit and Kronig introduce an idea of self rotation of the electron , which would naturally give rise to an angular momentum vector in addition to the one associate with orbital rotation (l , m).

-- Electron Spin magnetic moment   µs = -( e/2m) g s

                where e= charge  and      g  =  Lande - g - factor.

Thus , these four quantum numbers play an important role to determine the value of radius , energy level (n), sub energy level (l), the orientation of  orbital(m) and  the direction of spin.

In other word " Quantum numbers serve as an address for an electron.

7. Electronic configuration of the Element..

According to Rutherford model of an atom, atom is made of outer electron cloud   (-vely charged electron) and inner nucleus (neutral neutron and +vely charged proton).Niels Bohr agreed with this concept , he also agreed that electron revolve round the nucleus like a planet moves round sun.He applied the Plank's quantum theory to the electron revolving round the nucleus
         The orbits , there fore called as energy levels or energy shells. Bohr gave numbers 1, 2, 3, ...etc to these energy levels, there are they now called as Principal quantum numbers.these energy levels are also designated by  k, l, m, n, etc...

The energy levels which are more far from the nucleus associated with greater amount of energy                                                        -The energy of outermost electron is greater than innermost.

-These outermost electron helps atom to react with other because they can pullout easily  from the orbital .

-Each shell made of many sub shells which are themselves composed of atomic orbitals.

-First shell K  have 1 sub shell = s

-Second shell L  = 2 sub shells = s , p

-Third shell M = 3 sub shells =s , p, d

-fourth shell N = 4 sub shells = s , p, ,d, f

No.	Sub shell	Name
1	s	Sharp
2	p	Principal
3	D	Diffused
4	f	fundamental

Shells	Sub shells	No. of electron	Type of sub shells found in shell	Distribution electron in sub shells
K	s	2	only s	1s
L	P	6	s ,p,	2s , 2p,
M	d	10	s, p, d,	3s , 3p, ,3d
N	f	14	s, p, ,d, f , d,	4s , 4p , 4d , 4f
…	g and so on	18…	s , p, d, f, g,…	Alphabetically  so on

-The reactivity of the element is highly dependent upon its electronic configuration.

- The distribution of electron in various orbital (s, p,d ,f ) is known as electronic configuration.

-Mathematically it is described by Slater rules.

-In representing position of electron in various shells and sub shells ,the following rules are observed..

=> Major  energy shells written first then sub shells and after that the no. of electron in particular sub shell

for example :-     

1s²,   where ,   1 represents the shell i.e. K

                        s represent the sub shell
                    and  2 indicates the no of electron present in sub shell.

-According to Afbau principal--

               The electrons enter in the various orbitals in the order of increasing energy.

- According to pauli exclusion principal--

                An orbital can contain a maximum of 2 electron and these two electrons must be in opposite spin.                                              

                                                                       

↑

↓

                                                            

-According to Hund's rule--

           It states that electron pairing in orbital of the same energy level will not take place unless all available orbitals of subshell contain one electron  each with parallel spin.   

Order of filling of electron in various orbitals is given below :--

Above picture shows normal periodic table of element, but from the picture given below we can find the outermost orbital of the element and electronic configuration.

There are some special cases of electronic configuration.
From periodic table we can see that the electronic configuration of the elements  are going in normal way till Argon(18) last electron goes in 3p orbital. But in case of Potassium(19) last electron should fill in 3d orbital but it is not so, it goes in 4s orbital instead of 3d orbital because 4s has low energy in comparison to 3d .Thus electron prefer to go in lower energy orbital then higher energy level.

-The next ten elements from ( Z=21 to 30) Sc to Zn are called Transition elements.
In these elements addition of electron take place in inner 3d orbitals while outer 4s orbital remains fully occupied.