I was interested in learning more about the history of the middle east, so I looked online for some books about it and I found something from the 6000 bc -500 bc and from 700 ad - today. As you can see there is a big hole between the 500 bc and the 700 ad, because I couldn't find any book about that time period. Can someone help me?
(Even if the book suggested doesn't start exactly in the 500 BC or end in the 700 AD it's good, also multiple books are good if there isn't only one)
The period you're missing could broadly be described as the "Persian" period of Middle Eastern history in contrast to the generally Mesopotamian dominant period before or the Islamic period after.
Unfortunately it's a bit difficult to find one book to cover the whole span because of the conquests of Alexander the Great and about 200 years of Macedonian rule under his successors. Typically books that really cover the whole span are focused on the Persian/Iranian dynasties and neglect the Macedonian Seleucids. Alternatively there are some that separate the Achaemenid Persians (550-330) from the post-Alexandrian dynasties. The latter are largely older or more expensive.
The best if you're trying to get it all in one book is probably Ancient Persia by Josef Wieshöfer. Even that only dedicates a small chapter to the Seleucids that may be better supplemented by an additional book like Land of the Elephant Kings by Paul J. Kosmin or Encyclopaedia Iranica articles. If you're going the "multiple books or articles" route then you may also choose The Persians by Maria Brosius instead of Wieshöfer which doesn't discuss the Seleucids at all.