Academic journal article The Science Teacher

Settling the Score: Exploring the Historic Debate over Atomic Bonding

Academic journal article The Science Teacher

Settling the Score: Exploring the Historic Debate over Atomic Bonding

Article excerpt

British scientist John Dalton (1766-1844), French scientist Joseph Louis Gay-Lussac (1778-1850), and Italian scientist Amedeo Avogadro (1776-1856) are familiar to many chemistry students. Such students may understand the importance of Dalton's atomic theory, model how Gay-Lussac's law relates the pressure and the temperature of a gas, and use Avogadro's number to correctly convert between the atomic and the macroscopic.

However, these historical scientists contributed far more to the development of modern chemistry than most students might realize. To illuminate their contributions, I designed a lesson grounded in Avogadro's settling of a debate between Gay-Lussac and Dalton on how atoms combine at the simplest level.

The story of the discovery of atomic bonding can improve students' basic understanding of chemistry. In the early 19th century, scientists were trying to differentiate between elements (containing a single type of atom) and compounds (more complex substances containing multiple types of atoms). They were also searching for the process by which atoms combine. The debate among Gay-Lussac, Dalton, and Avogadro is essential to this story.

During a two-day lesson, I introduce this historical debate before moving on to atomic structure and bonding. The resulting class discussion addresses the nature of science, promotes productive struggle, develops critical-thinking skills, and aligns with the Next Generation Science Standards (see box, p. 54).

Setting the stage

Dalton and Gay-Lussac held different views of how elemental gases combine to make more complex compounds. At the heart of their debate was the discovery that particles of some gaseous elements contain atoms that can bond with other atoms the same as themselves. We now call these diatomic molecules (e.g., [H.sub.2], [O.sub.2]). The recognition that particles can unite with themselves came from Avogadro's famous paper (1811). His hypothesis addresses the problems raised by Dalton's analysis of the comparative densities of different gases, while also applying Gay-Lussac's law of combining volumes, which states that gases combine in simple, whole-number ratios. Avogadro's paper also explained the observation that gaseous reactions can produce a larger volume than expected, a discrepancy that left Gay-Lussac confused.

Avogadro's discovery was also important in correctly determining the atomic weight of elements. Because weighing a single atom was impossible, scientists such as Dalton worked on formulating a system of relative atomic weights based on comparison. One can see how the discovery of diatomic molecules was important to determining elements' correct atomic weights. For further historical background, see "On the web."

How history can highlight the nature of science

The Next Generation Science Standards (NGSS) point out that the nature of science can be presented through historical case studies (NGSS Lead States 2013, Appendix H). Studying how a theory emerged and changed over time helps students understand abstract and hard-to-comprehend concepts (Clary and Wandersee 2013). Struggle is an important part of science, and Solomon et al. (1992) note that "mature scientists also had to struggle to see phenomena in a new way" (p. 419). Historical scientific controversies help students understand that scientists try to resolve disagreements by testing additional hypotheses through further research (Clary and Wandersee 2013).

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The activities

Day 1

To engage students, I ask a question they can easily answer: "What is the chemical formula of water?" Then I press them: "How do you know?" By taking textbooks and teachers at their word, the students often reply, but suddenly they wonder how we know the chemical formulas of different substances. Students break into groups of three or four to read the case studies summarizing the major arguments made by each scientist (see "On the web") and to develop particle-level models. …

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