As previously mentioned, the preposition “a” can be combined with the articles a, as, o, and os to become à, às, ao and aos.
As far as demonstratives are concerned, a can only be contracted with the following:
a + aquela = àquela
a + aquelas = àquelas
a + aquele = àquele
a + aqueles = àqueles
a + aquilo = àquilo
If you were paying attention in the Demonstratives unit, you may have noticed that este, esta, isto, esse, essa, isso are absent. These are never contracted with the preposition “a”.
Finally, note the direction of the grave accent on the: à, which happens as a result of the preposition “a” being contracted with a pronoun starting with “a” (eg. à or àquele). Make sure not to confuse the à with á.