The purpose of this study was to investigate Grade 10 Thai students about their understanding on inter- and intramolecular forces. Sixty four students were elicited by administered open-ended questions after finishing normal instruction on chemical bonding topics. The instrument was in a set of open-ended questions which contained a number of systematic elicited questions, but only six questions were reported here. It was found that the students had difficulty in understanding inter- and intramolecular forces. Even though they had learned these conceptions in chemistry class, the students were not able to distinguish between inter- and intramolecular forces. The implications of this research indicated that making students understand chemistry concepts and principles was not an easy task. There are numerous ways in which students can misconstruct concepts and principles largely due to failing of shifting between macroscopic and microscopic phenomena. Teachers must be aware of the various conceptions, otherwise, the alternative conceptions will be the obstacle to understand more complex conceptions on learning chemistry. Appended to this document is "Questions Used to Elicit Students' Conceptions." (Contains 7 tables and 2 figures.) [This paper was presented at the 2010 National Association for Research in Science Teaching (NARST) Annual International Conference, Philadelphia, PA, Mar 21-24, 2010. This study was funded by the Institute for the Promotion of Teaching Science and Technology, Thailand.]