Lewis Dot Structure Notes

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 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 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 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.

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.

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 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.