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Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

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Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
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Chirality in Nature02:30

Chirality in Nature

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Chirality is the most intriguing yet essential facet of nature, governing life’s biochemical processes and precision. It can be observed from a snail shell pattern in a macroscopic world to an amino acid, the minutest building block of life. Most of the snails around the world have right-coiled shells because of the intrinsic chirality in their genes. All the amino acids present in the human body exist in an enantiomerically pure state, except for glycine - the sole achiral amino acid.
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Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

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Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than...
47.5K
Imperfections in Crystal Structure: Stoichiometric Point Defects01:26

Imperfections in Crystal Structure: Stoichiometric Point Defects

133
Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
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Chirality02:25

Chirality

23.1K
Chirality is a term that describes the lack of mirror symmetry in an object. In other words, chiral objects cannot be superposed on their mirror images. For example, our feet are chiral, as the mirror image of the left foot, the right foot, cannot be superposed on the left foot.
Chiral objects exhibit a sense of handedness when they interact with another chiral object. For example, our left foot can only fit in the left shoe and not in the right shoe. Achiral objects — objects that have...
23.1K
Potential Due to a Polarized Object01:29

Potential Due to a Polarized Object

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A neutral atom consists of a positively charged nucleus surrounded by a negatively charged electron cloud. When placed in an external electric field, the external electric force pulls the electrons and nucleus apart, opposite to the intrinsic attraction between the nucleus and the electrons. The opposing forces balance each other with a slight shift between the center of masses of the nucleus and the electron cloud, resulting in a polarized atom. On the other hand, a few molecules, like water,...
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Related Experiment Video

Updated: Apr 24, 2026

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation
10:33

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

Published on: February 27, 2019

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Density functional theory for chiral nematic liquid crystals.

S Belli1, S Dussi2, M Dijkstra2

  • 1Institute for Theoretical Physics, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|September 13, 2014
PubMed
Summary

The thermodynamic stability of chiral nematic (cholesteric) liquid crystal phases is explained by a new density functional theory. This theory predicts entropy-driven ordering in chiral particles, clarifying the origin of cholesteric states.

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Area of Science:

  • Physical Chemistry
  • Materials Science
  • Soft Matter Physics

Background:

  • Chiral nematic (cholesteric) liquid crystals were the first liquid crystal phases observed experimentally.
  • The fundamental reasons for the thermodynamic stability of cholesteric states remain unclear.
  • Understanding this stability is crucial for developing advanced materials and technologies.

Purpose of the Study:

  • To elucidate the origin of thermodynamic stability in chiral nematic (cholesteric) liquid crystal phases.
  • To develop a theoretical framework for predicting the equilibrium pitch of chiral particle systems.
  • To investigate the factors influencing the handedness of the cholesteric phase.

Main Methods:

  • Development of a density functional theory tailored for chiral particles.
  • Application of the theory to systems of right-handed hard helices.
  • Analysis of the interplay between local nematic alignment and excluded-volume effects.

Main Results:

  • The density functional theory successfully predicts an entropy-driven cholesteric phase.
  • The predicted phase can exhibit either right- or left-handed chirality.
  • The handedness is dependent on particle shape and thermodynamic conditions (e.g., temperature, density).

Conclusions:

  • The study provides a theoretical explanation for the thermodynamic stability of cholesteric liquid crystal phases.
  • Chiral ordering arises from the combined effects of local nematic alignment and differences in excluded volume between particle pairs.
  • The findings offer insights into the design and control of chiral liquid crystal materials.