Modeling In Chemistry

[Breanna Mangels]

Sincethe summer of 1999, groups of modeling teachers have worked at Arizona State University to organize the topics students ordinarily study in high school (and introductory college) chemistry around a series of particle models of increasing complexity. In 2005 we began an effort to develop a Modeling Workshop for chemistry with a design parallel to that used in the Modeling Workshop in mechanics. In June 2005 we conducted a pilot workshop in chemistry at ASU. Since then nearly 2500 teachers have taken Modeling Chemistry workshops nationwide.

In traditional chemistry curricula, students are introduced right away to the modern model of the atom and asked to accept all its complexities as a matter of faith. By contrast, our approach is to start with a simple model of the atom and show students that our model evolves as the need for a better one arises. In each of the instructional units we follow this sequence:

Our treatment of the role of energy in both physical and chemical change is sufficiently different from the piecemeal approach found in most curricula that you will want to review it pretty thoroughly before you attempt to teach it. We have also included two evaluation instruments:

The slide show exhibits the storyline we have used to uncover chemistry. The curriculum materials have undergone testing at our high schools for ten years and have been used in workshops since 2005. Major contributors include Joy Shrode, Brenda Royce, Larry Dukerich, Ray Howanski, Tammy Gwara and Dr. Guy Ashkenazi. If you have any questions, comments or concerns, you should direct them to Larry Dukerich or Brenda Royce.

First-time Modeling Workshop attendees qualify for a free one-year membership to AMTA. Members have access to ALL instructional resources, webinars, distance learning courses, and other membership services!AMTA members have access to ALL instructional resources, webinars, distance learning courses, and other membership services!

I am enrolled in a Modeling Instruction Workshop in Michigan. We have only four days left of the 15 scheduled days. I had planned to blog about the workshop every day, but I found that it was difficult for me to articulate my thoughts quickly enough to post daily. I know several teachers that are using the Modeling Curriculum, including Erica Posthuma Adams. You may have seen her posts here at ChemEd X highlighting ideas from Modeling Instruction so I was not unfamiliar with the term. But, I must admit that I had developed several misconceptions about Modeling Instruction before seeing it for myself.

My biggest "AH HA " has been that I had assumed Modeling Instruction was a curriculum that used models. When I say models, I am visualizing having students create models and draw models to represent what is happening on a particle level. That perception understated the method immensely. What I have discovered is that the Modeling Instruction curriculum is a vehicle for a conceptual pedagogy that teachers use to lead students to a conceptualization of chemistry concepts. Teachers use whiteboards and other modeling tools as formative assessment to uncover misconceptions and help students develop their own model of the atom and how it relates to chemistry content. This approach mirrors how the field of chemistry naturally evolved. Because of this, the order of topics must be addressed in a specific order.

As I am trying to wrap my head around using the modeling curriculum this fall, one of my biggest hurdles will be adjusting to the idea that I will not be teaching my students about the nucleus of the atom, electron configurations or the organization of the periodic table during first semester! There is some flexibility in the order of topics, but the curriculum is written to address the following Big Ideas:

I have been using many activities that provide models for students to manipulate with the desire to help them understand a concept. The Modeling Instruction curriculum provides lab experiences so that students discover evidence that their previous model cannot explain. Then, the student develops a new model to accomodate that new evidence. This is parallel to how science evolves every day.

I also appreciate that the curriculum develops conceptual understanding of the relationships and ratios in chemistry as opposed to emphasizing algorithmic problem solving. I have become a big fan of using the BCA format for stoichiometry instead of using dimensional analysis/factor label method.

I would love to hear from others that are using modeling instruction. I am interested in hearing success stories, but I am also interested in difficulties that teachers have had in making the transition.

I'm so glad to hear you are enjoying your workshop! I too had the same inaccurate perception that modeling instruction was just going to show me how to incorporate more models into my curriculum. It is SO MUCH MORE. I have learned more about pedagogy, learning theory, and chemistry in my involvement with the AMTA than I did in any of my pre-service training. I highly suggest following #modsci, #modchem, and #modphys on twitter to connect with other teachers using Modeling Instruction.

Do you use the entire curriculum? Do you cut and paste from your previous curriculum? I am worried about missing some of the standards in our Michigan Framework, but maybe I can just modify the curriculum a little. The presenters at my workshop have said that it will be difficult for a first year modeler to complete the entire curriculum. Since I am practiced in using inquiry, some white boarding and some socratic questioning technique, I am hoping that I will be able to move along adequately. Do you have hints, suggestions for keeping on pace?

good conversation so far! Having not been exposed to a modeling workshop yet, I'm wondering about the extent to which the 'natural curiousity' that Larry expects to exploit to engage students in this approach extends to the phenomena we present to them...so does the BB ('Democritus atom') sufficiently excite the students to join the adventure of developing models to account for the properties and interactions we observe in each system we encounter? I have read through several of the modules so far and I'm wondering if that's a place we could possibly improve upon, as well as the discourse practices employed during the whiteboarding, which seems to still emphasize the teacher 'guiding' the conversation rather than the students do so?

Having just completed the workshop, I have no first hand experience for evidence of student engagement. I did feel as I completed many of the activities provided in the curriculum that I wished I had been taught in this way. I felt it was a more intuitive approach. I excelled at memorization of algorithmic facts, but my high school self was annoyed that I always knew what the results of our laboratories should be before I completed them. I wanted to discover things for myself.

ChemEd X invites practitioners in the chemistry education community to share their experiences, knowledge and the resources they use in their classroom and laboratory. ChemEd X includes teachers and faculty from many diverse educational settings and who serve all students. We encourage contributions that demonstrate the particular opportunities found in teaching chemistry to diverse audiences from the entire breadth of learning environments.

Context. Recent observations of the HDO/H2O ratio toward protostars in isolated and clustered environments show an apparent dichotomy, where isolated sources show higher D/H ratios than clustered counterparts. Establishing which physical and chemical processes create this differentiation can provide new insights into the chemical evolution of water during star formation and the chemical diversity during the star formation process and in young planetary systems.

Aims. We seek to determine to what degree the local cloud environment influences the D/H ratio of water in the hot corinos toward low-mass protostars and establish which physical and chemical conditions can reproduce the observed HDO/H2O and D2O/HDO ratios in hot corinos.

Conclusions. This work demonstrates that the observed differentiation between clustered and isolated protostars stems from differences in the molecular cloud or prestellar core conditions and does not arise during the protostellar collapse itself. The observed D/H ratios for water in hot corinos are consistent with chemical inheritance of water, and no resetting during the protostellar collapse, providing a direct link between the prestellar chemistry and the hot corino.

Understanding the formation and evolution of water during star and planet formation is essential to our understanding of the conditions for life in other planetary systems. Water is a prerequisite for life as we know it and, furthermore, also an important molecule for the planet formation process: it contributes significantly to the solid mass reservoirs outside the ice line and impacts the thermal evolution of the gas and the coagulation of dust particles (see, e.g., van Dishoeck et al. 2014).

It is well established that water predominantly forms on dust grain surfaces during the molecular cloud phase, where water constitutes the bulk of the ice (e.g., van Dishoeck et al. 2014). The evolution from the onset of star formation, through the protostellar collapse and protoplanetary disk phases, and finally onto planetary bodies is however still uncertain. Key questions include to what degree water is processed during star and planet formation, namely, whether planets accrete pristine water inherited from the molecular cloud, or if the water is a product of local processes within the envelope and disk. Crucially, it remains unclear to what extent variations in the local cloud environment impact the water chemistry of the final planetary system, and hence ultimately influence the conditions for biology in extrasolar systems.

As the water chemistry appears to be mainly inherited from the environment (i.e., the molecular cloud), the question becomes whether and how the large-scale environment can impact the water chemistry of the final planetary system. In a recent work, evidence for a correlation between the HDO/H2O ratios and the local cloud environment is observed. Jensen et al. (2019) find a higher HDO/H2O ratio towardisolated protostars than what has previously been detected toward sources in clustered environments. The authors proposed two explanations for such a correlation: (1) either temporal differences between isolated and clustered cores: a slower collapse of an isolated prestellar core could prolong the prestellar core phase leading to a higher D/H ratio in the water, or (2) higher temperatures or a stronger radiation field in clustered cores, where nearby (proto)stars and turbulent cloud dynamics may heat the gas compared to isolated counterparts. Chemical diversity induced by variations in the natal cloud environment have scarcely been studied theoretically, as the majority of physicochemical models of protostellar collapse have utilized one-dimensional models that fail to capture the complex nature of star formation indynamic molecular clouds. If local cloud variations drive a difference in the D/H ratio of water in the hot corino phase, such a difference may also impact the complex organic molecules (COMs) which are characteristic of hot corinos and hot cores. In a recent study, Aikawa et al. (2020) simulate the impact of various prestellar core conditions on the abundance of COMs and warm carbon chain chemistry (WCCC) in hot corinos. These authors findthat the WCCC is more pronounced in cores with lower initial temperature, lower extinction, or a longer prestellar core phase. No clear pattern emerged for the hot corino chemistry; some molecules, such as CH3 OH, are less abundant when the temperature is higher, while other molecules show no impact of variation in prestellar core conditions.

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