Molecule
A molecule is the smallest fundamental unit of a chemical compound that retains the chemical properties of that compound. Molecules are made up of two or more atoms bonded together, which can be either of the same element or different elements.
Composition
Molecules can vary in size from diatomic molecules like hydrogen (H2) or oxygen (O2), to large macromolecules like proteins and DNA. Here are the key aspects:
- Atomic Bonds: Atoms within a molecule are held together by chemical bonds, which include covalent, ionic, and metallic bonds. The most common in molecular structures is the covalent bond, where atoms share electrons.
- Types of Molecules:
- Homonuclear: Composed of atoms of the same element (e.g., O2).
- Heteronuclear: Made from atoms of different elements (e.g., H2O).
- Structure: Molecules can have various shapes, determined by the type of bonds and the arrangement of atoms, influencing their properties and reactivity.
History
The concept of molecules dates back to ancient times when philosophers like Democritus proposed the idea of 'atomos' or indivisible units of matter. However, the modern understanding of molecules began with:
- John Dalton in the early 19th century, who developed the atomic theory, which suggested that elements are made of atoms and that compounds are combinations of atoms in whole number ratios.
- Avogadro's Law (1811) by Amedeo Avogadro, stating that equal volumes of gases at the same temperature and pressure contain an equal number of molecules.
- The development of X-ray crystallography in the 20th century allowed scientists to determine the precise structure of complex molecules.
Context
Molecules are fundamental to all fields of science:
- In chemistry, they are the basis of chemical reactions, where bonds are broken or formed.
- In biology, molecules like DNA, proteins, and lipids are crucial to life processes.
- In physics, molecular interactions explain phenomena like diffusion, osmosis, and phase transitions.
- In materials science, understanding molecular structures aids in the development of new materials with desired properties.
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