States, Structure and Bonding

• Structure and bonding affect melting and boiling points depending on how much energy is needed to get the atoms, ions or molecules apart
• The stronger the bonds are , keeping the particles together, the more heat energy you'll need to overcome those bonds and separate the molecules
• Describe the bonds of simple covalent substances.

  They have strong bonds within each molecule but only weak molecular forces between the molecules, therefore they have low melting and boiling points as it doesn't take much energy to overcome these forces
• Why do most metals have high melting + boiling points?

  Because the metal ions are very strongly attracted to the sea of delocalised electrons, and need lots of heat energy to overcome the attraction
• Why do ionic substances have high melting + boiling points?

  The positive and negative ions in ionic lattices are strongly attracted to each other and so the electrostatic attraction means the ionic substance will have a high m.p and b.p
• Describe why giant covalent structures have a high melting + boiling points.

  Since giant covalent lattices are held together by strong covalent bonds , they take a lot of energy to break
• Define "sublime"

  When a substance goes straight from a solid to a gas - some giant covalent structures sublime