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A topic from the subject of Contributions of Famous Chemists in Chemistry.

  • 1 year ago
  • 6 min read
The Discovery and Application of X-Ray Crystallography by Sir William Henry Bragg
Introduction

X-ray crystallography is a technique that uses X-rays to determine the structure of crystals. It was discovered by Sir William Henry Bragg in 1912 and revolutionized chemistry by providing a way to determine the structure of molecules and crystals. This information has been instrumental in developing new materials, drugs, and disease treatments.

Basic Concepts

X-rays are a type of electromagnetic radiation with a wavelength shorter than visible light but longer than gamma rays. When X-rays interact with matter, they can be scattered or absorbed. The scattering of X-rays by crystals is the key to determining the crystal's structure.

Crystals are materials with a repeating arrangement of atoms or molecules. This arrangement is called the crystal structure, which can be determined by measuring the scattering of X-rays.

Equipment and Techniques

X-ray crystallography utilizes an X-ray diffractometer, consisting of an X-ray source, a sample holder, and a detector. The X-ray source emits X-rays directed at the sample, held in place by the sample holder. The detector measures the intensity of the scattered X-rays.

Several techniques measure X-ray scattering, with the powder diffraction method being the most common. This method uses a powdered sample to determine the average crystal structure.

Types of Experiments

The most common X-ray crystallography experiment is the single-crystal experiment, using a single crystal to determine the detailed structure. Other types include powder diffraction (for average structure determination) and fiber diffraction (for fiber-shaped materials).

Data Analysis

Data from X-ray crystallography experiments is analyzed using computer programs to determine the crystal structure. The program calculates the electron density of the crystal—a map of the electrons—which reveals the positions of atoms and molecules.

Applications

X-ray crystallography has broad applications in chemistry, including:

  • Determining the structure of proteins
  • Determining the structure of DNA
  • Determining the structure of drugs
  • Developing new materials
  • Understanding the structure of inorganic compounds
Conclusion

X-ray crystallography is a powerful technique that has revolutionized chemistry by enabling the determination of molecular and crystal structures, leading to advancements in materials science, medicine, and other fields.

The Discovery and Application of X-Ray Crystallography by Sir William Henry Bragg
Introduction
X-ray crystallography, a groundbreaking technique developed by Sir William Henry Bragg, revolutionized the study of crystal structures in chemistry. Discovery
In 1912, Bragg and his son, Lawrence Bragg, discovered that X-rays diffract (bend) when passing through crystals. This diffraction pattern provides information about the arrangement of atoms within the crystal. Bragg's Law
Bragg's Law, proposed by Bragg and his son, describes the conditions for X-ray diffraction:

nλ = 2d sin θ

where:
  • n is an integer (order of diffraction)
  • λ is the X-ray wavelength
  • d is the interplanar distance in the crystal
  • θ is the diffraction angle
Application in Chemistry
X-ray crystallography allows the determination of:
  • Crystal structures
  • Interatomic distances and bond angles
  • Molecular shapes
  • Unit cell parameters
  • Crystallographic planes
Impact
The discovery of X-ray crystallography enabled:
  • A deeper understanding of crystal structures in materials science
  • Advancement of the fields of mineralogy, biology, and medicine
  • The development of new materials and pharmaceuticals
Recognition
Sir William Henry Bragg and his son received the Nobel Prize in Physics in 1915 for their pioneering work in X-ray crystallography. Conclusion
The discovery and application of X-ray crystallography by Sir William Henry Bragg revolutionized chemistry, providing invaluable insights into the structure and properties of materials at the atomic level.
Experiment: The Discovery and Application of X-Ray Crystallography by Sir William Henry Bragg
Introduction

This experiment demonstrates the principles of X-ray crystallography, a technique pioneered by Sir William Henry Bragg and his son, William Lawrence Bragg, in the early 1900s. X-ray crystallography allows scientists to determine the atomic and molecular structure of crystalline materials by analyzing the diffraction patterns produced when X-rays interact with the crystal lattice. This experiment will simplify the process for illustrative purposes.

Materials (Simplified Demonstration)

For a simplified demonstration illustrating the principles, you'll need:

  • A laser pointer (simulates the X-ray source – note: lasers are not X-rays and this is a conceptual analogy)
  • A diffraction grating (acts as a simplified representation of a crystal lattice)
  • A screen or wall to project the diffraction pattern onto
  • Ruler
Procedure (Simplified Demonstration)
  1. Shine the laser pointer through the diffraction grating.
  2. Observe the diffraction pattern projected onto the screen.
  3. Measure the distances between the diffraction spots or lines on the screen.
Observations (Simplified Demonstration)

You will observe a pattern of bright spots or lines on the screen. The spacing between these spots or lines is related to the spacing between the grooves (analogous to atoms in a crystal) in the diffraction grating and the wavelength of the laser light (analogous to X-rays).

Analysis (Simplified Demonstration)

While a full calculation using Bragg's Law (nλ = 2d sinθ) requires more advanced equipment and precise measurements (including the angle of diffraction, θ), this simplified demonstration visually illustrates the fundamental principle: the spacing of the diffraction pattern directly relates to the spacing of the grating (crystal lattice). The further apart the spots, the closer the spacing within the grating.

Significance

X-ray crystallography revolutionized our understanding of matter at the atomic level. It's been instrumental in determining the structures of countless molecules, including proteins (like hemoglobin and enzymes), DNA, and various minerals. This knowledge underpins advancements in medicine, materials science, and numerous other fields.

Note:

A true X-ray crystallography experiment requires specialized and potentially hazardous equipment. This simplified demonstration using a laser and diffraction grating serves only to illustrate the basic principles of diffraction and its relationship to crystal structure.

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