The stamps are still valid.
However the minimum price for an airmail letter is now $1.10 so one stamp would not be enough i'm afraid.
Bri0626 here on the forum sells US stamps, maybe she could help you out with some 5/10c stamps? I don't know what "make up value" stamps USPS has but here in the UK we have 1p,2p,5p,10p,20p etc.