Everybody knows that quello means ‘that’ and bello means ‘nice or beautiful,’ however now and then you might have read or listened to the forms ‘quegli/begli’, quei/bei, quel/bel.
Let’s start from quello
You should be able to distinguish when quello is used as a pronoun (replacing a noun) and when used as adjective (accompanying a name).
In the first case quello has four different possible endings, -o/-a/-i/e, according to the noun to which they refer
- Quello è il mio gatto – That one is my cat
- Quelle sono le mie amiche – those are my girlfriends
In the second case, when quello is an adjective it changes endings with the same patterns as in the definite articles, depending on the nouns following..
- Quei ragazzi
- Quegli amici
- Quel ragazzo
- Quella donna
- Quelle ragazze
The adjective bello also follows the pattern of the demonstrative quello
- Bei ragazzi
- Begli amici
- Bel ragazzo
- Bella donna
- Belle donne
To apply the above rule, both quello and bello must be positioned before the noun; they must be adjectives to the noun.