Three students were discussing their ideas about chemical bonds. This is what they said:

Janre: “I think a chemical bond is produced by a molecule. It is a substance made up of matter that holds atoms together.”

Will: “I think a chemical bond is an attraction between atoms. It is not made up of matter.”

Leta: “I think a chemical bond is a structural part of an atom that connects it to other atoms.”

The purpose of this assessment probe is to elicit students’ ideas about chemical bonds. The probe is designed to find out if students think bonds are physical matter or attractions between electrons.

atoms or molecules, chemical bonds

The best response is Will’s. A chemical bond is an attraction between atoms; it is not made up of matter that holds atoms together, and it is not a structural part of an atom. Two or more atoms are linked together by chemical bonds. There are several types of chemical bonds, including covalent bonds, ionic bonds, metallic bonds, and hydrogen bonds. Chemical bonds are formed between atoms as a result of an attraction between their electrons. The bond exists as an attractive force between the atoms where electrons are transferred or shared.

The concept of chemical bonds far exceeds the ideas expected of students at the elementary level. However, upper elementary students have often seen representations of molecules and may begin to form the “ball-and-stick” idea that there is a structure or “glue” holding particles together.

In middle school, students develop the idea that atoms join together to form molecules or crystalline arrays. They encounter the term chemical bond in both life science and physical science and have a concept of atoms being joined together, but an understanding of the mechanism by which electrons are shared or transferred, resulting in an attraction that holds atoms together, exceeds the middle school level. Students at this level see a variety of representations of molecules and ionic substances, including ball-and-stick models, which may contribute to their conception of a physical chemical bond. They learn that models, such as physical and graphic models of molecules and crystal arrays, do not entirely represent the real thing. These models can be used without going into details about the formation or types of chemical bonds.

Students at this level develop a deeper understanding of the microscopic nature of molecules, atoms, and parts of atoms, including the types of chemical bonds formed by the interaction of electrons. The nature of the atom, including its interaction with other atoms, is still an abstract, difficult idea for many students. Because representations of molecules and compounds, including physical models and symbolic drawings, are commonly used in high school science, it is important to take the time to determine whether students have a conception of a chemical bond as a physical entity or a force of attraction. Many students can define the types of chemical bonds and the mechanism in which atoms are joined together yet still harbor the common misconception that a chemical bond is a structural component of a substance or a glue-like form of matter.

This probe is appropriate for middle school and high school students, although middle school students should not be expected to know the detailed mechanism of bonding.

• An extension of the idea that atoms “need” to form bonds is that atoms “make decisions” about forming bonds. This may come from analogies used in teaching such as holding hands or finding a new partner (Barker 2004).
• In general, students have difficulty in developing an adequate conception of the chemical combination of elements until they can interpret combination at the molecular level (Driver et al. 1994).
• Students have difficulty interpreting the use of ball-and-stick models for ionic lattices. Twenty-seven Australian 17-year-olds were interviewed in a study by Butts and Smith (1987) using a ball-and-stick model of sodium chloride. Students confused the six sticks around each ball as “one ionic and five physical bonds.” Only two of the students mentioned that the sticks were used merely to hold the balls in place for the model (Driver et al. 1994).