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:]^-
  • 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.