Final answer:
In a Lewis diagram, the more electronegative atom receives the extra electrons and carries a partial negative charge. The central atom is typically the least electronegative, except for hydrogen and the halogens, which are usually terminal atoms.
Step-by-step explanation:
When drawing a Lewis diagram, the element that gets the extra electrons is C) the more electronegative atom. Electronegativity is a measure of how strongly atoms attract bonding electrons to themselves. In a molecule, the atom with the greater electronegativity will acquire a partial negative charge because it attracts the shared electrons more strongly. This is indicated by the delta symbol (δ-) for a partial negative charge and a crossed arrow to show the direction of greater electron density. For instance, in a water molecule (H2O), the oxygen atom has a higher electronegativity than the hydrogen atoms, making it attract electrons more and thus, it bears a partial negative charge while the hydrogen atoms carry a partial positive charge.
Additionally, when considering the placement of atoms in a molecule, the central atom is usually the least electronegative element. For example, in carbon dioxide (CO2), carbon is the central atom because it is less electronegative than oxygen. Hydrogen and the halogens are usually terminal atoms because of their respective electronegativity and available bonding sites.