Recording-2025-02-12T22:04:04

Carbon Dioxide and Electromagnetic Radiation

• Molecular vibrations: Carbon dioxide (CO2) can experience vibrations due to electromagnetic radiation when exposed to light.

• Vibrational modes:

  • There are three distinct vibrations in carbon dioxide molecules: asymmetric stretch, bending mode, and others.

  • Electromagnetic radiation can move the oxygen atoms in one direction and the carbon atom in the opposite direction, leading to infrared activity if the frequency of vibration matches that of infrared light.

Infrared Spectrum of CO2

• Analyzing infrared spectrum reveals different vibrational modes:

  • Asymmetric stretch vibration corresponds to specific wave numbers indicating energy levels.

  • Bending mode occurs at approximately 500 wave numbers, relating to molecular shape and behavior.

  • Higher wave numbers correlate with higher vibrational energy within the molecular structure.

Importance of Molecular Vibrations

• These vibrations are crucial for understanding the interactions of CO2 in Earth's atmosphere.

• Vibrational characteristics of CO2 impact how energy is emitted or absorbed from Earth, crucial in climate studies and understanding greenhouse gases.

Interpretation of Satellite Imagery

• Image reflections from Earth demonstrate different absorption and reflection characteristics:

  • White areas indicate reflected clouds, blue for oceans, green for plants absorbing light.

  • Plants absorb blue and red light, reflecting green.

• Absorption Spectrum: The spectrum of sunlight changes when observed from space, with specific absorption lines indicating interactions with atmospheric molecules.

• On Earth, CO2 does not absorb much sunlight; however, it significantly absorbs infrared emissions.

VSEPR Theory: Molecular Shape Determination

• Valence Shell Electron Pair Repulsion (VSEPR) Theory: Used to predict molecular shapes based on electron repulsion.

• Like charges repel, so electron groups around a central atom arrange to minimize repulsion:

  • Linear arrangement occurs for molecules with two electron groups, ideal angle less than 180 degrees.

  • Trigonal planar arrangement (ideal 120 degrees) for three electron groups—seen in molecules like boron trifluoride.

  • Tetrahedral arrangement (ideal 109.5 degrees) for four groups; lone pairs alter expected angles (e.g., ammonia 107.3, water 104.5 degrees).

Influence of Lone Pairs on Molecular Geometry

• Presence of lone pairs creates deviations in bond angles due to greater repulsion compared to bonding pairs.

  • Molecules may adopt different geometries based on number and arrangement of lone pairs.

  • Trigonal bipyramidal: Five groups (e.g., phosphorus pentafluoride); lone pairs affect positioning (equatorial preferred for lower repulsion).

  • Octahedral geometry: Six electron groups, with varying shapes based on lone pair presence, like square pyramidal or square planar for molecules such as iodine pentafluoride.

Summary of Molecular Shapes Based on Electron Pair Arrangements

• Key shapes and bond angles:

  • Linear: 180 degrees.

  • Trigonal Planar: 120 degrees.

  • Tetrahedral: 109.5 degrees.

  • Trigonal Bipyramidal: 120 degrees (equatorial) and 90 degrees (axial).

  • Octahedral: 90 degrees for all interactions.

• Each structure's stability and geometry are determined by minimizing electron repulsions, aiding in predicting molecular behaviors and reactivity.