Also, the singular "lo" and "la" is usually elided before vowels, becoming "l'".
Prepositions (di, a, da, in, con, su) followed by a definite article usually join in one word. The preposition di+ article (del, dello, dalla, dei, degli, delle) is called partitive article and corresponds to the English "some, any, no" (example: Hai del denaro? = Have you got any money?).