Chapter 2 - Structure and properties

Chapter 2

Ionic compounds have high melting points and boiling points because of the mainly strong electrostatic forces of attraction between oppositely charged ions in the giant lattice. Ionic compounds will conduct electricity when molten or in solution because the ions are able to more freely around in the liquids. 

Non-metals react together to form molecules which are held together by covalent bonds. These hold the atoms together very strongly. If these substances are made of simple molecules, they have low melting points and boiling points. So at room temperature they often exist as gases and liquids or as solids which melt relatively easily.

Giant covalent structures contain many atoms joined by covalent bonds. They have high melting points and boiling points. Diamond is a very hard substance because the carbon atoms in it are held strongly to each other. However, graphite is soft because there are layers of atoms which can slide over each other. They can do this because there are no covalent bonds between its layers.

The positively charged energy in metals are held together by delocalised electrons. These also allow the layers to slide over each other so that the metal's shape can be changed. They also allow the metal to conduct electricity and heat.

The polymer chains in a thermosoftening polymer form a tangled web. The polymer softens at relatively low temperatures. Other polymers have strong covalent bonds between their chains which form cross links. We call these thermosetting polymers.

Nanoscience is the study of small particles that are between 1 and 100 nanometers in size. (1nm + 1 x 10(-9)m)

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