Chapter 4 Notes | Chemistry 1st Year
“Liquids And Solids”
- Intermolecular Forces
- Liquid Crystals
- Crystal Lattice
- Crystals And Their Classification
- Classification of Solids
- Determination of Avogadro’s Number
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- Among three states of matter i.e. gases, liquids and solids, the intermolecular attractive forces in the gases are negligible. In liquids intermolecular forces are strong enough to keep the molecules close together. Anyhow, the molecules in liquids are free to move with respect to one another.
- There are four types of intermolecular forces i.e. dipole-dipole forces, London dispersion forces, hydrogen bonding and Ion-dipole forces. The relative strenghts of sipole-dipole and dispersion forces depend upon the polarity, polarisability, size and shape of the molecules.
- The vapour pressure of a liquid measures the tendency of a liquid to evaporate. It is the pressure exerted by the vapours on the surface of a liquid when the rate of evaporation is equal to the rate of condensation.
- Many crystalline solids melt to give a turbid liquid before melting to give a clear liquid. These turbid liquids possess some degree of order and care called liquid crystals.
- In crystalline solids the particles are arranged in a regular and repeating manner. The essential structural features of a crystalline solid can be represented by its unit cell. The three dimensional array of points representing atoms, ions or molecules is called crystal lattice.
- The simplest unit cell is a cubic unit cell. There are seven crystal systems overall.
- The properties of solids depend on the arrangement of particles and the attractive forces b/w them. Ionic solids are hard and brittle and have high melting points. Covalent solids consist of atoms held together by covalent bonds and these bonds extend throughout the solid.