Final answer:
(NH₄)₂SO₄ cannot be considered a molecular compound when considering Lewis diagrams and the octet rule because it contains an ion, the sulfate ion (SO₄²⁻).
Step-by-step explanation:
(NH₄)₂SO₄ cannot be considered a molecular compound when considering Lewis diagrams and the octet rule because it contains an ion, the sulfate ion (SO₄²⁻). The sulfate ion violates the octet rule because the sulfur atom has more than 8 valence electrons.
When drawing a Lewis diagram for (NH₄)₂SO₄, we can see that the nitrogen (N) atoms each have 5 valence electrons and the hydrogen (H) atoms each have 1 valence electron. The overall molecule is neutral because of the double positive charge of the ammonium ion (NH₄⁺). Therefore, (NH₄)₂SO₄ is an ionic compound rather than a molecular compound.