Chemistry- Ionic Radii of alkali metals?

This is a review question for my test which will be tomorrow...Compare and contrast the ionic radii of any alkali metal and any halogen. Explain whether they are bigger, smaller, or the same size as their neutral atom. ....."I'm not exactly sure how to figure out if they are bigger, smaller or same. Is it if you loose electrpons its smaller and if you gain it is bigger? Please expalin fully with examples! Thankyou!!!"