Boiling is not simply a temperature phenomenon. It is primarily related to vapor pressure which is, of course, influenced by temperature. This Powerpoint presentation explains what vapor pressure is. The presentation explores the relationship between temperature and vapor pressure. It also defines the normal boiling in terms of vapor pressure and atmospheric pressure. Vapor pressure graphs are used to examine boiling points at other pressures.
Free worksheets for this topic, and the vapor pressure table, are available on my website at http://evanschemistrycorner.com.