How much do Oxford look at predicted A-Level grades?Watch
is a bit out of date but hopefully its still somewhat relevant. They still will care about gcses a lot but don't rly care about the personal statement.
Specifically for chemistry, I got better predicted grades than I was expecting (3 A*) and I was wondering if this would decrease other parts of a potential application i make like the personal statement or any interviews i get?
As username4215970 has pointed out, the ATs will be grading your application against a set of criteria, and some elements of an application will be given heigher weighting than others. In a blog, LMH Principal, Alan Rusbridger, once described how some candidates applications were so strong that, by the time of interview, they would have been offered a place simply for stating their name correctly.
Predicted A* grades are generally given high weighting, so 3A*s is a great start. Conversely, your PS is unlikely to weigh so heavily, as these are quite liable to be coached and written to suggest a spurious "excellence".
Having said that, the competition for Oxford is so high that no part of your application can be weak. And just to add an element of randomness, weighting is not uniform between subjects or from year to year.