Electron excitation

Electron excitation is a general term for any interaction between a photon (particle of light) and an electron. It refers to the process where an electron in an atom or molecule gains energy and jumps to a higher energy level

Electrons can be excited by various sources, such as:

  • Photoexcitation: This specifically refers to the absorption of a photon by an electron, leading to the electron’s transition to a higher energy level. This excited state can have various consequences, depending on the system involved. For example, it can trigger chemical reactions, cause fluorescence, or lead to the emission of other photons.
  • Collisional excitation: This occurs when an energetic particle (another electron, ion, etc.) collides with an electron, transferring some of its kinetic energy to the electron and promoting it to an excited state.
  • Thermal excitation: When atoms or molecules vibrate due to heat, this energy can be transferred to their electrons, exciting them to higher energy levels. This plays a crucial role in many chemical reactions and physical phenomena.
  • Chemical excitation: During chemical reactions, the rearrangement of electrons creates and breaks bonds, often resulting in excited states within the participating molecules.
  • Impact excitation: In certain materials like semiconductors, bombarding the material with high-energy particles (e.g., electrons, ions) can directly excite electrons.
  • Electrostatic excitation: Applying a strong electric field can create an external force on electrons, potentially pushing them to higher energy levels.
  • Field ionization: In very strong electric fields, electrons can be ripped out of their atomic or molecular orbitals altogether, resulting in a highly excited state before reaching the vacuum level.
Electron excitation in practice
  • Electrons within atoms can be excited and jump to higher energy levels. This process, driven by sources such as light or heat, plays a crucial role in many aspects of chemistry and physics. The key principles of electron excitation are:
    • Energy levels: Each orbital in an atom has a specific energy level, with lower levels being closer to the nucleus and higher levels further away. The difference in energy between levels determines the amount of energy needed to excite an electron.
    • Transitions: When an electron is excited, it moves from its ground state (lowest energy level) to an excited state (higher energy level). The specific excited state it jumps to depends on the amount of energy absorbed or transferred.
    • De-excitation: Electrons in excited states are unstable and eventually return to their ground state. This can happen through:
    • Emission of light (photons): In this process, called spontaneous emission, the electron releases the excess energy as a photon with specific energy corresponding to the energy difference between the excited and ground states.
    • Non-radiative processes: Sometimes, the electron transfers its energy to another atom or molecule through collisions or other interactions, instead of emitting light.
Carbon atom example
  • Ground State Configuration: In the ground state, a carbon atom has its six electrons arranged as follows: 1s^2 2s^2 2p^2. This means two electrons are in the 1s orbital (closest to the nucleus), two in the 2s orbital, and two in the 2p orbital.
  • Energy Level Differences: Each orbital has a specific energy level, with the 1s being the lowest and the 2p being higher in energy. This is because electrons experience a stronger pull from the positive nucleus the closer they are.
  • Electron Excitation: When a carbon atom absorbs energy (light or heat), one of the 2s electrons can be excited to an empty spot in the 2p orbital.
  • Energy Efficiency: This transition requires less energy compared to exciting an electron from the 1s orbital due to the difference in energy levels. Imagine the 2s and 2p orbitals as steps on a staircase; climbing from the 2s step (lower energy) to the 2p step (higher energy) requires less effort than climbing directly from the 1s step (much lower energy).
  • Electron stability: The excited electron in the 2p orbital is unstable and wants to return to its ground state. It can do this by releasing the absorbed energy in different ways:
    • Emitting light: The electron releases the energy as a photon of light, causing the carbon atom to fluoresce.
    • Non-radiative processes: The energy is transferred to other atoms or molecules through collisions or vibrations without emitting light.
Light SourceDescriptionSub-atomic ProcessMechanismVisible LightNaturalArtificial
luminescenceAny process where atoms or molecules emit light. See Bioluminescence, Chemiluminescence, Electroluminescence,
Fluorescence
Electron ExcitationVarious mechanisms involving energy transitions in atoms/moleculesVaries (depends on mechanism)Yes (some mechanisms)Yes (various technologies)
BioluminescenceA form of luminescence:
Light emission by living organisms
Electron Excitation
Chemical reactions initiated and controlled by biological systems within living organisms.YesYesYes
ChemiluminescenceA form of luminescence:
Light emission from chemical reactions
Electron Excitationhemiluminescence relies solely on the chemical energy stored within the reacting molecules.Varies (depends on reaction)Yes
(natural and synthetic)
Yes (glow sticks, analytical tools)
ElectroluminescenceA form of luminescence::
Light emission due to electric fields
Electron ExcitationApplied electric field excites electrons in materialsYesNoYes (LEDs, displays)
FluorescenceA form of luminescence:
Light emission from certain materials after absorbing light
Electron ExcitationTemporary absorption of light, followed by emission of a different (lower energy) color.YesYes
(minerals and plants)
Yes
(dyes, pigments, glow sticks)
Photoluminescence
Light emitting diodeA type of electroluminescence
Semiconductor diode emitting light when current flows
Electron transition
(recombination)
Recombination of electrons and holes in semiconductors releases energy as photonsYesNoYes
Lasers
(Light amplification by stimulated emission of radiation)
A type of photoluminescenceLight amplification by stimulated emission of radiationExcited atoms/molecules release photons, stimulating further photon emission and amplifying lightYesNoYes
Stellar lightNuclear fusionFusion of hydrogen nuclei releases enormous energy, including lightYesYesNo
FireChemiluminescence & Blackbody radiationHot objects emit light (incandescence), and chemical reactions create excited molecules (chemiluminescence)YesYesYes
LightningPlasma processesHot, ionized gas (plasma) emits light through various mechanisms like recombination and BremsstrahlungYesYesNo
Neon signsGas dischargeElectric current excites gas atoms, which emit light upon returning to lower energy levels (similar to fluorescence)YesNoYes
Light bulbs (Incandescent)Blackbody radiationHot filament emits light due to thermal excitation of electronsYesNoYes
SunlampsUltraviolet radiationEmit UV light, causing fluorescence in nearby materialsNo (UV)NoYes
References
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Summary