$$\text{CO}_2$$ and $$\text{SiO}_2$$ are the oxides of elements of same group but $$\text{CO}_2$$ is a gas but $$\text{SiO}_2$$ is solid. Why?

PLACEHOLDER ANSWER - the answer is an explanation. Small carbon forms strong $$p\pi$$-$$p\pi$$ double bonds with oxygen, giving discrete linear $$\text{O} = \text{C} = \text{O}$$ molecules held together only by weak van der Waals forces, so $$\text{CO}_2$$ is a gas. Larger silicon cannot form stable $$p\pi$$-$$p\pi$$ bonds, so each Si forms four single Si-O bonds in a giant three-dimensional covalent network, making $$\text{SiO}_2$$ a hard, high-melting solid.