The Quantum Mechanical Model of Atom

Charge-cloud model of atom is based on the solution of Schrödinger Equation

Quantum number

Name

Allowed values

Number of allowed levels.

Effect on electron energy

n (shell)

Principal

1,2,3,4,5…

KLMNO

Any

Strong

l (subshell)

Orbital

0,1,2,3…n-1

s,p,d,f…

n

Moderate

ml

Orbital magnetic

-l,-l+1,…0, …,l-1,l

2l+1

Weak

ms

Spin

2

2

Weak

Quantum Numbers of Electron Configurations

Main energy level (shell)

Energy sublevel (subshell)

Maximum number of electrons per shell 2(2l+1)

Maximum number of electrons per shell 2n2

n=1

s

2

2

n=2

s

p

2

6

8

n=3

s

p

d

2

6

10

 

18

n=4

s

p

d

f

2

6

10

14

 

 

32

Explaining the Periodic Table

  1. Principal of minimum energy: An atom is stable when its total energy is a minimum.

  2. Pauli exclusion principle: Only one electron can exist in any particular quantum state in an atom.

 

The order of filling the orbitals.

1s

     

2s

2p

   

3s

3p

3d

 

4s

4p

4d

4f

5s

5p

5d

5f

6s

6p

6d

6f

7s

7p

7d

7f

Examples:

Helium= 1s2

Neon= 1s22s22p6

Sodium= 1s22s22p63s1

Silicon= 1s22s22p63s23p2

Chlorine=1s22s22p63s23p5

Argon= 1s22s22p63s23p6

Properties of elements

Families of elements

Electronic structure

Chemical properties

Nobel gases

Closed shells

Inert, passive.

Alkali metals

A single s electron in the outer shell.

React violently with water.

Alkaline earth metals

Two s electrons in the outer shell.

React with water, but not violently.

Transition elements –metals

The outer shell is not empty or complete

Not very reactive.

Halogens

One electron is missing from completing a shell

Very reactive nonmetals