Coordinate Bonds (HL IB Chemistry)

What are coordinate bonds?

• In simple covalent bonds the two atoms involved share electrons
• Some molecules have a lone pair of electrons that can be donated to form a bond with an electron-deficient atom
  • An electron-deficient atom is an atom that has an unfilled outer orbital

• So both electrons are from the same atom
• This type of bonding is called dative covalent bond or coordinate bond
• An example of a dative bond is in an ammonium ion
  • The hydrogen ion, H⁺ is electron-deficient and has space for two electrons in its shell
  • The nitrogen atom in ammonia has a lone pair of electrons which it can donate to the hydrogen ion to form a coordinate bond

Dative covalent bonding ammonium ion

Ammonia (NH₃) can donate a lone pair to an electron-deficient proton (H⁺) to form a charged ammonium ion (NH₄⁺)

• More examples of coordinate bonding can be found in the section on Lewis Structures