Chemical Structure

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The map above shows one way in which chemical structure can be organised. However, several different terms are used to refer to the same structures, so take some care.

By understanding the behaviour of particles, and how they are arranged, chemists can explain and predict how materials behave, and make new materials with properties to suit a particular purpose.

Where we have substances in the solid state, their particles are arranged in a lattice. A lattice is a regular arrangement of particles, whether these are atoms, ions or molecules. The chemical bonding, including intermolecular bonding, is important.

There are four main types of solid structure: three are giant structures, the fourth a molecular structure (small and big covalent molecules). These are:

Chemical StructureParticlesChemical Bonding
Giant Ionic LatticeIonsIonic Bonding (throughout)
Giant Molecular Lattice
(Giant Covalent, Covalent Network,
or Giant Atomic Lattice if preferred)
AtomsCovalent Bonding (throughout)
Giant Metallic LatticeMetal ions with delocalised electronsMetallic Bonding (throughout)
Molecular Lattice
(Simple Covalent - small and big molecules)
MoleculesCovalent Bonding between atoms forming molecules;
Intermolecular Bonding between separate molecules

Types of chemical structure with regard to solid state

The table below relates types of chemical structure and some properties.

Chemical StructureElectrical ConductivityMelting PointRange of
Boiling Points
(°C)
Solubility in Water
solidliquid
Giant Ionic LatticeNoYesHigh700 to 3600Generally good, but may be low owing to high lattice enthalpy
Giant Molecular LatticeNoNoVery High2000 to 6000Poor
Giant Metallic LatticeYes (high)Yes (high)Low to Very High357 to 6000Poor, but some metals react with water
Molecular LatticeNoNoGenerally Low-253 to +600Generally poor, but some substances react with water

Types of chemical structure and their properties

Crystallography

In the solid state, it is the internal orderliness of the particles (atoms, ions, molecules) of an element or compound that characterises the recognisable external shape of its crystals. The angles at which the surfaces (faces) of a crystal meet each other are a characteristic and reproducible property. Since earliest civilisation these geometrical patterns have been of interest, and particulary since the invention of the microscope. The study of such patterns is the science of crystallography. However, to examine the internal stuctures of crystals requires the use of X-ray radiation in a technique called X-ray crystallography. This involves measuring the degree to which crystals reflect or scatter radiation. X-ray radiation is used because their wavelengths are of the same order of magnitude as the distance apart of the atoms in crystals. The idea was experimentally verified by Max von Laue in 1912.

In 1913 William Henry Bragg and William Lawrence Bragg (father and son) calculated the spacing between layers of atoms by measuring the intensities of X-rays reflected from crystals at different angles. They were awarded the Nobel Prize for Physics in 1915 for their work.

X-ray analysis is a powerful method of examining orderly arrangements of particles in crystals, crystalline powders, and large molecules like those of proteins and polymers.


Giant Ionic  ½  Covalent Network  ½  Covalent Molecular  ½    Giant Metallic


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