I would rather help you to understand something before a lab or test, than to find out you don't understand it while grading your work. Only absences notified ahead of time may be excused. Barring exceptional circumstances, all subsequent missed exams will receive a grade of zero. Because students often work in groups in lab, absences hurt everyone and should be avoided. In addition, many days there will be graded homework problems assigned.
Many students find it useful to keep a copy of the problem to review.
No late homework will be accepted and the lowest homework grade will be dropped. If you must be absent, have someone else take notes and hand in any assignments for you. There will be a Periodic Table quiz given in lab - you will be given a blank periodic table and asked to fill it in with the proper symbols. For certain elements, the properly spelled name will be required. Other quizzes are possible.