The Lewis structure of CO2 consists of the symbol for carbon, C, connected to two oxygen symbols surrounded by four dots each. The connections are both made with two parallel lines. Each chemical symbol represents one atom.
The lines represent double covalent bonds. Lewis structures are constructed using the octet rule as a guide. Each atom has an outer shell of electrons, called valence electrons, that are shared with other atoms in chemical bonds. Atoms usually favor having eight valence electrons, and they share valence electrons with other atoms in covalent bonds. Carbon has four valence electrons, and oxygen has six. When a carbon atom double bonds with two oxygen atoms, each oxygen atom gains two electrons to create a full octet, and carbon gains four. Lewis structures represent valence electrons that are not involved in covalent bonding using dots.