shapes of atomic orbital and rules for filling of orbital

Day 1
4.5.20
Good Morning Boys,
Today we will discuss about the shapes of Atomic orbital, energies of orbital and rules for filling of electron in the orbitals of atom.
Learning Objective :
 students will be able to

• Draw the shapes of various atomic orbital.
• understand the concept of degenerate orbitals.
• Learn the rules for filling electron in atom.

Quick review of Quantum No Concept :

Quantum Number
Symbol
Values
Principal
n
1,2,...
Angular Momentum
l
0,1,2,...,n-1
Magnetic
m
-l to +l
Spin Magnetic
s
+1/2,-1/2

Shapes of Orbital:

• 
• 
  
• s   orbital:  Spherical in shape, non-directional. It has only 1 orbital therefore, can accommodate only 2 electrons.

• p-orbital:   dumb-bell shaped and directional. It has 3 orbital i.e px, py, pz.(p–orbital have three different orientations. These are designated as px, py & pz depending upon whether the density of electron is maximum along the x y and z axis) It can accommodate maximum of 6 electrons.

• d-orbital:   It is double dumbbell shaped, directional. It has 5 orbital (dxy,dyz,dzx,dx2-y2,dz2).Out of the five orbitals, the three (dxy, dyz, dzx) project in between the axis and the other two dz² and  dz²-y²  lie along the axis. It can accommodate maximum of 10 electrons

• f-orbital:   It has diffused shape. It has 7 orbital therefore, can accommodate maximum of 14 electrons.

Points for reference :

1. Shielding effect or screening effect:

Due to the presence of electrons in the inner shells, the electron in the outer shell will not experience the full positive charge of the nucleus. So, due to the screening effect, the net positive charge experienced by the electron , from the nucleus (effective nuclear charge ) is lowered . 

2. Nodal surfaces /Nodal Points and Planes  or simply nodes :

The point where there is zero probability of finding the electron is called nodal point. There are two types of nodes: Radial nodes and angular nodes.

 Radial nodes is concerned with distance from the nucleus. 

Angular is concerned with direction.


No. of radial nodes = n – l – 1

No. of angular nodes = l
Total number of nodes = n – 1

Nodal planes are the planes of zero probability of finding the electron. The number of such planes is also equal to l. 

Degenerate orbitals: Orbitals having the same energy are called degenerate orbitals. Shape of p and d-orbitals.

Rules For Filling  electron in orbitals of atom :

Aufbau Principle:

In the ground state of the atoms, the orbitals are filled in order of their increasing energies.

  The order in which the orbitals are filled is as follows:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s...

 the direction of the arrow gives the order of filling of orbitals.

Note :

n+l rule-

Orbitals with lower value of (n+l) have lower energy. 

If two orbitals have the same value of (n+l) then orbital with lower value of n will have lower energy.

Pauli Exclusion Principle:

"No two electrons in an atom can have the same set of four quantum numbers."

 Only two electrons may exist in the same orbital and these electrons must have opposite spin.

Hund’s rule of maximum multiplicity:

Pairing of electrons in the orbitals belonging to the same subshell (p, d or f) does not take place until each orbital belonging to that subshell has got one electron each i.e., it is singly occupied.

( This is due to the fact that electrons being identical in charge, repel each other when present in the same orbital. This repulsion can, however, be minimized if two electrons move as far apart as possible by occupying different degenerate orbitals. All the electrons in a degenerate set of orbitals will have same spin. )

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