### Clue: Then beat bad grade after one term in chemistry (7)
### Answer: ISOTOPE 
 ### Explanation: Definition: term in chemistry
 [ SO(then, as in "and so/then to bed" + TOP(to beat;to surpass) + E(a bad grade, in any alphabetical grading system) ] **placed after**(after, in an across clue) I(Roman numeral for "one").
Defn: … for one of two or more forms of the same element with atoms containing a different number of neutrons.