Final answer:
The Lewis structures for each molecule or ion are: a) H2O - H-O-H, b) CO2 - O=C=O, c) NH4+ - H-N-H, and d) SO3 - O=S=O.
Step-by-step explanation:
a) H2O:
In a Lewis structure, the central atom is surrounded by its valence electrons and the shared electrons with other atoms. In the case of H2O, oxygen (O) is the central atom. Oxygen has 6 valence electrons and hydrogen (H) has 1 valence electron. Therefore, the structure is H-O-H, with the oxygen atom having 2 lone pairs of electrons on it.
b) CO2:
For CO2, carbon (C) is the central atom. Carbon has 4 valence electrons and oxygen has 6 valence electrons. The structure is O=C=O, with each oxygen atom sharing 2 electrons with the carbon atom.
c) NH4+:
NH4+ is a cation with a positive charge. The central atom is nitrogen (N). Nitrogen has 5 valence electrons and each hydrogen atom (H) has 1 valence electron. The structure is H-N-H, with the nitrogen atom having 3 lone pairs of electrons.
d) SO3:
The central atom in SO3 is sulfur (S). Sulfur has 6 valence electrons and each oxygen atom has 6 valence electrons. The structure is O=S=O, with each oxygen atom sharing 2 electrons with the sulfur atom.