AKTU: Engineering Chemistry UNIT 1 | PART 1 | QuickShot

SUMMARY 

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1. Atomic and Molecular Structure

• Molecular Orbitals of Diatomic Molecules:
  These are formed when atomic orbitals combine. They can be bonding (stabilizing) or antibonding (destabilizing). Examples include molecular orbitals in $H_2$, $O_2$, and $N_2$.

• Bond Order:
  Bond order tells us the strength and number of bonds between atoms. It is calculated using the formula:

  $$\text{Bond Order} = \frac{\text{Number of electrons in bonding orbitals - Number of electrons in antibonding orbitals}}{2}$$

  Higher bond order = stronger bond. For example, bond order for $O_2$ is 2.

• Magnetic Characters:
  Molecules can be paramagnetic (attracted to magnets, due to unpaired electrons, e.g., $O_2$) or diamagnetic (repelled by magnets, due to paired electrons, e.g., $N_2$).

• Numerical Problems:
  Questions often involve calculating bond order or identifying magnetic properties based on the molecular orbital diagram.

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2. Chemistry of Advanced Materials

• Liquid Crystals:

  • Introduction:
    Liquid crystals are materials that flow like liquids but have some molecular order like solids. They are in-between states of matter.

  • Types:

    1. Nematic Liquid Crystals: Molecules are aligned in the same direction but can move freely.
    2. Smectic Liquid Crystals: Molecules are organized in layers and more ordered than nematic.
    3. Cholesteric Liquid Crystals: Molecules form a helical structure with layers reflecting light, creating color patterns.

  • Applications:

    1. Displays: Used in LCD screens for TVs, phones, and monitors.
    2. Thermometers: Used in color-changing thermometers.
    3. Biomedical Sensors: For detecting changes in pressure or temperature.
    4. Industrial Applications: Used in devices like tunable lasers.

• Industrially Important Liquid Crystals:
  Materials like 5CB (4-Cyano-4'-pentylbiphenyl) and MBBA (N-(4-Methoxybenzylidene)-4-butylaniline) are used because of their stability and effectiveness in forming displays or other devices.