I posted a while back, but I (and two of my friends) was (were) accepted to Yale weeks ago and I spoke to professor on the phone from the department who told me that they do not directly admit students to their graduate program but have to recommend their admission to the graduate school who makes final admission decision. I spoke to the professor at the end of January and I was officially admitted by the end of the first week in Feb. At that point, the professor made the impression that the department had already recommended who they wanted and all other notifications were out their hands. They stated that the graduate school was taking longer than normal this year to send out acceptances. Acceptances came out quickly after that phone call but it also the graduate school who sends out rejections.
Keep in mind that not every chemistry department can directly admit you to their program, several can only recommend your admission and the graduate school will have final say. That is why notification from the graduate school is the only official acceptance.