Lewis Dot Structure Notes

Lewis Dot Structures

Valence Electrons

• Valence electrons are the number of electrons in the outermost shell.
• The number of valence electrons for elements in a group is consistent (Helium is an exception).
  • Group 1 elements have one valence electron.
  • Group 2 elements have two valence electrons.
  • Group 18 elements have eight valence electrons (except Helium, which has two).
• Metals usually do not participate in covalent bonds.
• Non-metals (in green) usually participate in covalent bonds.

Hydrogen (H₂)

• Hydrogen has one valence electron.
• Hydrogen needs one more electron to have a stable outermost shell, like helium (two electrons).
• Hydrogen shares its one valence electron.
• Two hydrogen atoms share their electrons to form a covalent bond.
• Lewis dot structure: H-H (a single line represents a bond between two electrons).

Oxygen (O₂)

• Oxygen has six valence electrons.
• Oxygen needs two more electrons to satisfy the octet rule (eight electrons in the outermost shell).
• Oxygen shares two electrons.
• Two oxygen atoms each with six valence electrons, share two electrons to form two bonds.
• Lewis dot structure includes showing lone pairs (non-bonding electrons).
• The final Lewis structure for O_2 is O=O with two lone pairs on each oxygen atom.

Nitrogen (N₂)

• Nitrogen has five valence electrons.
• Nitrogen needs three more electrons to satisfy the octet rule.
• Nitrogen shares three electrons.
• Two nitrogen atoms, each with five valence electrons, share three electrons to form a triple bond.
• Final Lewis structure for N_2 is N≡N, with one lone pair on each nitrogen.

Water (H₂O)

• Oxygen is the central atom because hydrogen is always on the side.
• Oxygen has six valence electrons and shares two.
• Each hydrogen has one valence electron and shares one.
• Final Lewis structure: Oxygen is bonded to two hydrogen atoms with two lone pairs on the oxygen atom.

Ammonia (NH₃)

• Nitrogen is the central atom (hydrogen is always on the side).
• Nitrogen has five valence electrons.
• Each hydrogen shares one electron to form a single bond with nitrogen.
• Lewis structure: Nitrogen is bonded to three hydrogen atoms, with one lone pair on the nitrogen atom.

Carbon Dioxide (CO₂)

• Carbon has four valence electrons and needs four more.
• Carbon is the central atom because it is the leftmost element on the periodic table compared to oxygen.
• Each oxygen atom needs to share two electrons.
• Carbon forms a double bond with each oxygen atom.
• Final Lewis structure: O=C=O, with two lone pairs on each oxygen atom.