Ionisation and excitation

Question 1

Describe excitation of electrons

Answer 1

Electrons with minimum E are in the ground state

Excitation: Electrons within an atom can be excited to higher energy levels when heat or other forms of energy are applied (i.e. absorption of a photon).
~The energy absorbed MUST equal the energy difference between the excited and initial states of the electron
~The excited state that is formed is not stable and short-lived.
~Thus the electron rapidly transits to a lower energy simultaneously emitting energy in the form of a photon (energy corresponds to energy difference between final and initial states).
-of lower energy

Question 2

Describe luminescence (types).

Answer 2

Luminescence- energy transitions from higher to lower states are accompanied by the emission of radiation in the form of photons. 2 types:
Flourescence – spontaneous deexcitation releasing a photon (occurs at 10-5 - 10-7s)
The electron can transition into a metastable state from which transition into the ground state is not allowed (δl ≠ +-1), a metastable state.
Phosphorescence – an electron remains in the metastable state and emits radiation at a later time

Question 3

What is ionisation?

Answer 3

Ionisation: occurs when an e- absorbs energy hf greater than its binding energy (the work that must be done/energy that must be supplied to completely remove an e- from an atom).
~the energy absorbed must overcome the electrostatic forces holding the proton to the electron
The remainder of energy is converted to kinetic energy of the e- and the e- is able to escape the atom. Photoeffect

Question 4

What are the equations related to ionisation and excitation?

Answer 4

E + Eb = 0

Eb=-E

E= Eb + Ek Photoeffect

hf= Eb + ½mv2
where hf is the energy absorbed

Question 5

What is the binding energy and how does it vary?

Answer 5

~Binding energy (ionization potential) varies.

• Lowest values are for valence electrons
• Heavy atoms have much higher binding energies (Z2 x higher than in the H atom)

a positively charged ion is formed by ionization
an ionized atom is not stable. i.e. electron loss increases the energy of the system
the atom tends to return to it’s ground state with simultaneous emission of fluorescent radiation