CTS Guide: Atoms and Molecules, pp 146-147- Section IV Research Summaries
Concept of an Atom
At the high school level, students usually have an incomplete conceptual model of an atom that does not include electric interactions (Stevens, Delgado, and Krajcik 2010).
Middle school students often have difficulty distinguishing between atoms and molecules (Devetaka and Glazara 2010).
Atomic theory is difficult for many students. Even though they may memorize that “atoms are the building blocks of matter,” they have a difficult time connecting an atomic model with their observations (Treagust, Chittleborough, and Mamiala 2003).
Several studies of students’ initial conception of an atom show that they perceive it either as “a small piece of material” or the “ultimate bit of material obtained when a portion of material is progressively subdivided.” Such “bits” are thought to vary in size and shape and possess properties similar to the properties of the parent material. For example, some students consider atoms of a solid to have all or most of the macro properties that they associate with the solid, such as hardness, hotness/coldness, color, and state of matter (Driver et al. 1994, p. 74).
Concept of a Molecule
Middle school students often have difficulty distinguishing between atoms and molecules (Devetaka and Glazara 2010).
A correct understanding of a single, a collection, or combination of atoms is directly related to the concept of molecules (Stavy and Tirosh 2000).
Even though students may indicate that they know about cells, they may say that living systems are made of cells not molecules, because students often only associate molecules with physical science (NRC 1996).
Understanding how molecules make up other small objects such as cells may be tied to difficulty students have understanding how small something is (Driver et al. 1994).
Arnold (1983) showed how students confuse cells with molecules. When he asked students ages 14–15 to indicate whether certain things were made up of cells, molecules, or both, things that were living or once living were designated as being made up of cells but not molecules. Even molecules studied in biology such as carbohydrates and proteins were thought to be composed of cells, not molecules. Arnold concluded that students seem to confine the concept of a molecule to contexts encountered in physical science classes or instructional units.
Atomic Particles
Schmidt, Baumgärtner, and Eybe (2003) found that many high school students in their study sample thought there had to be the same number of neutrons as protons in a “standard” atom. Their reasoning for this often mentioned the idea that the neutrons “neutralized” the protons or “neutralized” the forces between the protons. Students thought this was necessary to keep the atom stable since they believed the neutrons repelled each other. Students who knew what isotopes were recognized that isotopes had a different number of neutrons. The researchers also found that students developed certain rules for atoms. One example is the rule that in standard atoms the number ratio between protons and neutrons is 1:1. This 1:1 idea is useful to learners because it is a reasonable abstraction from other everyday experiences.
Size of Atoms and Molecules
Understanding the size of an atom is challenging. Some students think that all microscopic objects are of a similar size. For example, they may think that atoms and blood cells are about the same size (Mayer and Krajcik 2016).
A study of middle school students found an interesting misconception concerning the relative sizes of atoms and molecules. Some students thought they could see atoms or molecules under a regular optical microscope in the same way they could see microbes. The researchers speculate that this misconception could arise from instruction, where students learned that atoms and microbes are tiny units, invisible to the naked eye. This may have caused them to believe that atoms are similar to microbes, or at least that they are of the same size (Nakhleh, Samarapungavan, and Saglam 2005).
Students may understand that an atom is too small to be seen with the unaided eye, yet they may believe it can be seen with a very powerful microscope (Harrison and Treagust 1996).
Some students, when recognizing the minute size of atoms, reason that because atoms are so small they have zero or negligible mass (Driver et al. 1994).
Some students believe that they could see molecules with microscopes or “magnifying lenses.” Even after instruction emphasized that most molecules are too small to be seen with even the most powerful microscope, some students, when asked if they could see molecules with microscopes, said: “Probably, maybe a little bit,” or “I think so, yeah, barely.” Some students thought molecules were comparable in size to other tiny objects they were familiar with such as dust, bacteria, and cells (Lee et al. 1993).
Properties of Atoms and Molecules
Several studies of students’ initial conception of an atom show that they perceive it either as “a small piece of material” or the “ultimate bit of material obtained when a portion of material is progressively subdivided.” Such “bits” are thought to vary in size and shape and possess properties similar to the properties of the parent material. For example, some students consider atoms of a solid to have all or most of the macro properties that they associate with the solid, such as hardness, hotness/coldness, color, and state of matter. Some students, when recognizing the minute size of atoms, reason that because atoms are so small they have zero or negligible mass (Driver et al. 1994) (Driver et al. 1994, p. 74).