Amount Substance
The Atom
Chemical Equations
Electron Arrangement
Group 2
Intermolecular Forces
Mass Spectrometry
States and Shapes

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Applied Chemistry Fundamental
Physical Chemistry

States and Shapes

States of Matter

Please also see bonding for information relating to this.

You must know the difference between solids liquids and gases by now so I won't patronise you, but there is some additional information. enthalpy of fusion is the energy needed to loosen forces holding particles together to go from solid to liquid. And enthalpy of vaporisation is the energy to overcome the forces holding particles together, making a gas.

As you can see in bonding there are several different types of crystal. Well, here are a furter two for you:

Molecular Crystals are covalent molecules held together by a form of intermolecular force. These crystals have low melting and boiling points; are not conductive and have varying solubilities.

Macromolecular crystals are huge structures like diamond and graphite. They generally have very high melting and boiling points are not conductive (apart from graphite which conducts electricity) and are insoluble.

Shapes of Molecules

Covalent molecules are made up of electron pairs. Which make a cloud of electrons. It is repulsion between these pairs that mean different molecules have different shapes. The below diagram shows the generalised shapes of molecules depending on how many electron pairs there are.

table of bond angles

However, it is not that simple, you have to take into consideration the fact that there are different types of electron pairs. lone pairs are much more repulsive than bonded pairs which are pairs being used in a bonds.

Therefore it logically follows that the repulsion between two lone pairs is strongest; then between a lone and bonded pair; and then two bonded pairs. What all this means is that the bond angles do in molecules do not comply with the idealised structure in the table above. For example, in water the bond angle between hydrogens is 105o, instead of the standard tetrahedral 109o28' (109 degrees 28 minutes).

Note A 'minute' in geometry is 1/60 (0.167) of a degree.