Key Concepts

Equations and relationships that you need to know:

• Postulates of the Quantum Theory
  
  
  1. Atoms and molecules can exist only in discrete states, characterized by definite amounts
     of energy. When an atom or molecule changes state, it absorbs or emits just enough en-
     ergy to bring it to another state.
  
  
  2. When atoms or molecules absorb or emit light in moving from one energy state to another,
     the wavelength of the light is related to the energies of the two states as follows:
     EEhigh-=low hc:
     m
  
  
  3. The allowed energy states of atoms and molecules are described by quantum numbers.
  
  
  
  


• h Planck s constant=='.6 626 10# -^34 particleJs:

= 6.626 × 10 –27erg ⋅sec

c = speed of light = 2.998 × 1010 cm/sec

E.

mole

∆ 1 196 10^5 kJ nm

$

= #$

m

.

E

n mole

kJ h

n

erg

(^1312) ν mc
218 10
22
11
2
$
:

=- == =

/

n

Zeff 1312 kJ mole

=dn 2

Zeff= Z −σ

where Zeff= effective nuclear charge, Z = actual nuclear charge, and σ= shielding or

screening constant

Rydberg-Ritz equation: ER

n

1

nH=- dn 2

E hchv R

nn

∆ H^11

if

===: : -

m dn^22

niand nfare quantum numbers

RH= 2.18 × 10 –18J = 109,737 cm–1

mrv::=nh 2 $r

EE e

a nn

z

2

11

ba

(^0) ab
22
-= > 22 - H
where n= quantum energy level
E= energy (at states aand b)
e = charge on electron
a 0 = Bohr radius
z= atomic radius
Part II: Specific Topics