Take a break to converse with colleagues in the hallway or over a cup of coffee. Attend evening social functions even if you are tired, and try to meet new people. Seek out a group that looks relaxed and happy. A good choice is one just joined by another person. Listen carefully for ways to assist them, such as putting them in contact with a colleague who has similar professional interests, providing a reference, or even working on joint projects.
Poster sessions are excellent networking opportunities for presenters and meeting attendees alike.
Attendees can discuss papers at length with authors and discover areas of mutual interest. Presenters can meet chemists interested in the same research area. Often speakers cannot do this during a conventional slide presentation at which the audience may be large, the speaking room dimly lit, and the time available for questioning limited. The fact that other students are taking the same course as you suggests common professional interests. Course breaks are good times to strike up conversations.