Teachers’ understanding of the particulate nature of matter: The case of Zambian pre-service science teachers

The purpose of this study was to assess Zambian Junior High School pre-service science teachers’ understanding of the particulate nature of matter. The results of this study show that most pre-service science teachers had good understanding about the number of particles, spaces between particles, and speed of particles when matter has been heated, melted, condensed, frozen, cooled, vaporized or compressed. This group of teachers also exhibited sound knowledge about the effect of compression on the size of particles as most of them correctly believed that the size of particles remain the same when a solid, liquid is compressed. However, less than half believed the size of particles remain the same when a gas is compressed. These findings are opposite of those reported in previous research studies (Gabel, Samuel, & Hunn, 1987; Valanides, 2000a; Valanides, 2000b; Nakhleh, Samarampungavan & Saglam, 2005; Boz, 2006; Yilmaz & Alp, 2006; Ozmen & Kenan, 2007). For example Ozmen & Kenan (2007) and Valanides (2000a) reported low levels of understanding of these aspects of particulate nature of matter among students and pre-service teachers, respectively. This group of Zambian pre-service science teachers’ better understanding of these four microscopic aspects of particulate nature of matter may be attributed to a longer period of instruction in chemistry and physics at high school level, grades 10-12. Chemistry and physics are among the compulsory subjects in Zambian national high school curriculum. Furthermore, the pre-service teachers took chemistry, physics, and biology courses in teacher education program before responding to a questionnaire for this study. However, we are making this attribution with caution because such a claim does not seem to be consistent with one previous study. For example, Boz (2006) reported that students had difficulties in applying the particulate nature of matter theory to explain phase changes even after instruction.

The results of this study also showed that most pre-service teachers displayed misconceptions on the size of particles because most of them believed that the size of particles in a substance increase when heat is applied and decrease when heat is removed. They also believed that the size of particles (molecules) increase or decrease when a gas is compressed. Similarly, Valanides (2000b) reported that the pre-service teachers attributed the expansion of a liquid to the expansion of the molecules themselves. Gabel et al (1987) also reported that pre-service teachers said atoms get larger as matter is changed from liquid to gas state. Such erroneous ideas suggest that most pre-service teachers in this study were unable to differentiate physical changes from chemical changes. Only a chemical change can affect the size of particles (atoms and molecules) of a substance. For example, the radius of an atom decreases after a loss of an electron. The cations (formed by the loss of electrons from the valence shell of the parent atom) are invariably smaller than their parent atoms. In some cases, the difference can be considerable (i.e. more than 50 percent). As cations have less number of electrons, the effective nuclear charge increases and as such, the remaining electrons are more tightly bound by the nucleus and, subsequently the radius of the cation is that of the compact atomic core. On the other hand, anions, which are formed by the gain of electrons by an atom—most commonly into the incomplete valence shell—are invariably larger than the parent atoms. In this case, the additional electrons repel the electrons that are already present, and the entire atom inflates.

This study also confirmed that misconceptions on the effect of physical change on the size of particles in a substance exist among all levels of students – from elementary to tertiary level. Such pre-existing beliefs are likely to influence how teachers learn new scientific knowledge that requires them knowing the particulate nature of matter. Such beliefs play an essential role in teachers’ instructional practice and subsequently in student learning. As such, the results of this study have implications for science teaching and learning and teacher education. For example, our results show that the pre-service teachers’ believed the size of the particles change (increase or decrease) when matter is heated, cooled, vaporized, condensed, frozen or compressed. Such a revelation of the pre-service teachers’ conceptions has direct bearing on the possible promotion of misconceptions among many generations of students they will teach. Furthermore, this group of teachers is likely to have difficulties to learn and understand gas laws and kinetic theory of matter because these topics require sound background knowledge about the particulate nature of matter.

Research shows that addressing teacher misconceptions seem to help eradicate students’ misconceptions in chemistry (Valanides, 2000a). Therefore, based on the results of this study and those reported in previous studies we recommend that chemistry teacher educators should identify misconceptions among the pre-service teachers before instruction on topics that require sound knowledge of particulate nature of matter. This will reveal the nature of misconceptions the pre-service teachers have on this topic. Then, teacher educators can take them into consideration when planning for instruction. We also recommend that teachers’ misconceptions should be addressed through learner centered teaching strategies. For example, the misconceptions held by the pre-service teachers in this study can be addressed by using interactive computer simulations and animations on particulate nature of matter. Computer simulations and animations would enable teachers to see that the size of particles and number of particles don’t change when there is a phase change. They would also see the effect of physical change on speed and spaces between particles in a substance. Similarly, teachers can be encouraged to discuss the particulate nature of matter in their classrooms using computer simulations and animations in order to help their students develop scientifically accepted concepts on the particulate nature of matter. However, a better intervention on the particulate of nature in schools would be more effective if teachers have sound knowledge about this topic and technological skills.