I am building a new house that will have an island countertop sink that will be 7 feet from the closest wall. How will I vent the 2 inch vent line??

You will install a "island loop vent". Click on; The Petch House: Kitchen Island Drains 101 to check them out. The only difference, in my area, is that we use two pipes instead of only one. One for the lower one for drainage and the upper one for a vent that connects back into the dry vent through the roof. More questions? I'm as close as a click. Tom