The Lewis structure for C2H4 consists of two "C" symbols connected by two lines; each "C" symbol is connected to two "H" symbols, with a single line for each. "C" represents carbon atoms, and "H" represents hydrogen atoms.
Lewis structures work off of the "octet rule," which notes that most atoms are most chemically stable when they have eight valence electrons, the electrons in an atom's outermost shell. An atom can share valence electrons with other atoms to satisfy this rule. Hydrogen is an exception, because its outermost shell can only be filled with two electrons. In Lewis structures, free valence electrons are represented by dots, and chemical bonds are represented by lines. In C2H4, each carbon atom has four valence electrons, and each hydrogen atom has one. The two carbon atoms share two electrons each with one another. They also share one electron each with two hydrogen atoms.