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Bonding

There are four main types of bonds, split into two groups. The strong primary bonds (Ionic, macromolecular covalent & metallic), and the weaker secondary bonds (molecular covalent and van der Waals):


Ionic

  • This is the electrostatic force of attraction between oppositely charged ions

  • It is formed by electron transfer: metal lose electrons while non-metals gain them

  • It is non-directional

  • High melting/boiling points

  • Easily soluble

  • Poor conductivity when solid, but when molten, charged ions are free to move around

  • Generally crystalline solids at room temperature & pressure

Covalent

  • This is formed from a shared pair of electrons

  • Typically occurs if an atom’s outer shell is about half empty (gaining/losing ~four electrons requires too much energy)

  • It is directional: the formation and orientation affects the overall molecular shape

There are two types:


Molecular Bonds (simple covalent):

  • These have a low melting and boiling point, due to the weak intermolecular forces

  • They have poor solubility in water

  • Conductivity is also poor, as there are no ions, and all electrons are fixed

  • Generally gaseous or liquidous at room temperature and pressure

Macromolecular Bonds (giant covalent):

  • These have very high melting and boiling points, as the bonds themselves are very strong and there are very many of them, so a vast amount of energy is required to break these

  • Insoluble in water

  • Mostly do not conduct, but graphite does

  • Generally solid at room temperature and pressure




Metallic

  • This is the electrostatic force between positive metal ions (cations) and a sea of delocalised electrons (which are negatively charged)

  • The cations are in regular rows, with the electrons free to move (hence conduct) around them</