This is miss-perception that if you have 500 words on a page or some other figure then Google boost up your ranking over search engine.
This is not right. Ranking is based on a dozen and dozens of factors and in addition more words on a page may assist, Google only understand the relevance of the page to the query – it doesn't inevitably mean the page will get good rank.
I have seen in Google Webmaster Help thread, John Mueller, a Google spokesperson, discussion about that.
Over there John is saying that there is no magic trick about number – the most crucial thing is how unique and worthful that content is.