Chemical Bonds

Ionic, Covalent, and Metallic Bonds

Chemical bond - when two or more atoms bind together

Octet Rule

When atoms combine to form molecules by either losing, gaining, or sharing their valance electrons until they attain eight outer shell electrons (noble gas configuration). Atoms are able to reach stability by doing so...

  • An exception to the octet rule would be boron, which only needs six valance electrons instead of eight in order to be stable.

Types of Bonds

The three main types of bonds are ionic, covalent, and metallic...

Ionic Bonds

Definition: the bonding between a non-metal (anion) and a metal (cation) that occurs when ions attract each other after one loses one or more of its electrons (metals + non-metals)

Examples:

  • NaBr - sodium bromide
  • NaCl - sodium chloride
  • KCl - potassium chloride

Properties:

  • Total transfer of electrons
  • High melting/boiling point
  • Soluble in water
  • Hard/brittle
  • No conductivity as a solid
  • Conductivity as a liquid and when dissolved
  • Crystal-like appearance

Covalent Bonds

Definition: a chemical bond formed by the sharing of a pair of electrons between atoms (non-metals + non-metals)

Examples:

  • NH3 - ammonia
  • H2 - hydrogen
  • H2O - water
  • CO2 - carbon dioxide

Types of Covalent Bonds:

  • Non-polar - when two atoms share a pair of electrons with each other
  • Polar - electrons forming the bond are unequally distributed

Properties:

  • Shared electrons
  • Low melting/boiling point
  • Sometimes soluble in water, sometimes insoluble
  • Relatively soft
  • No conductivity as a solid, liquid, or when dissolved (insoluble)

Metallic Bonds

Definition: chemical bond characteristic of metals in which mobile valence electrons are shared among atoms (metal + metal)

Examples:

  • Gold
  • Bronze
  • Aluminum

Properties:

  • High melting/boiling point
  • Insoluble in water
  • Shiny & ductile
  • Conductivity as a solid
  • Conductivity as a liquid

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