8. Properties of materials

• Typical solid has its particles very close together. Gives it a high density and makes it incompressible. Particles vibrate about fixed point and can’t move about freely. Typical liquid has similar density to solid and is virtually incompressible. Particles move about freely and randomly within liquid, allowing it to flow. Gases, particles have loads more energy and are much further apart. So density is generally pretty low and its very compressible. Particles move about freely,
• In simple covalent substances, covalent bonds don’t break during melting and boiling. To melt or boil simple covalent substances it needs to overcome weak intermolecular forces that hold molecules together. Don’t need to break strong covalent bonds that holds atoms together within molecules. Thats why simple covalent compounds have relatively low melting and boiling points. By contrast, to melt/ boil giant covalent substances, to break covalent bonds holding atoms together. That’s why giant covalent compounds have very high melting and boiling points
• Melting and boiling points-

  determined by strength of attraction between its particles. E.g. ionic compounds have much higher boiling / melting points than simple covalent substances - strong electrostatic attraction between ions requires lot more energy to break than weak intermolecular forces between molecules
• Electrical conductivity:

  Substance will only conduct electricity if it contains charged particles that are free to move, such as delocalised electrons in metal
• Solubility:

  solubility in water depends on type of particles that it contains. Water is polar solvent, so substances that are polar or charged will dissolve in it well, whereas non-polar or uncharged substances wont