What chemical aspect of amino acids results in their having different properties such that the chemical and physical properties of polypeptides vary with both amino acid content and amino acid order?
Sounds seriously like your homework, so it'd be better if you researched. However as a starting point amino acids can be polar and non-polar. These properties cause varying forces of attraction between amino acids and their surrounding environment. The location changes the way they can interact. Ask if you are unsure about something :)