Drawing Lewis Structures with Ions

Charge on Structures: Cyanide Ion (CN-)

  • Drawing Lewis dot symbols for carbon and nitrogen:
    • Carbon (C): 4 valence electrons
    • Nitrogen (N): 5 valence electrons
  • Carbon needs four electrons to complete its octet, while nitrogen needs three electrons.
  • Initial attempt to bond carbon and nitrogen:
    • Forms a triple bond between carbon and nitrogen.
    • Carbon still has one single electron.
  • Addressing the single electron on carbon:
    • The structure cannot be left with a single, unpaired electron.
    • The negative charge indicates an extra electron.
  • Adding the extra electron:
    • Add the extra electron to carbon to pair up the single electron.
    • This gives carbon a negative charge.
  • Resultant Lewis structure for cyanide ion (CN-): [:C≡N:]−[:C≡N:]^-
    • Carbon carries the negative charge (formal charge of -1).

Ammonium Ion (NH4+)

  • Nitrogen with four hydrogens: Nitrogen has 5 valence electrons, each hydrogen has 1.
  • Pairing hydrogen atoms with nitrogen electrons.
  • Addressing the positive charge:
    • The positive charge indicates the loss of an electron.
  • Removing an electron:
    • Remove an electron from nitrogen.
  • Resultant Lewis structure for ammonium ion (NH4+):
    • Nitrogen is bonded to four hydrogen atoms.
  • Nitrogen carries the positive charge (formal charge of +1).
  • Formal Charge: The charge an atom carries in a molecule or ion.

Nitrite Ion (NO2-)

  • Drawing single atoms: Nitrogen, Oxygen, and Oxygen.
  • Nitrogen: 5 valence electrons
  • Oxygen: 6 valence electrons each
  • Focus on valence electrons first, address the formal charge at the end.
  • Nitrogen in the middle: Connect two oxygen atoms to the central nitrogen atom.
  • Forming bonds:
    • Create a double bond on one side (N=O).
    • Single bond on the other side (N-O).
  • Addressing oxygen's electron needs:
    • Oxygen needs additional electrons.
  • Using the negative charge: The negative charge indicates an extra electron.
  • Adding the extra electron: Add the extra electron to the singly bonded oxygen.
  • Resultant Lewis structure for nitrite ion (NO2-):
    • One oxygen with a double bond to nitrogen, the other with a single bond and a negative formal charge.
    • The singly bonded oxygen carries a formal charge of -1.