Unit Overview
C.2 Structure & Properties of Matter

What causes lightning and why are some places safer than others when it strikes?

Unit Summary

What causes lightning and why are some places safer than others when it strikes? This unit is designed to help students build a deeper understanding of atomic structure and atomic-scale force interactions through exploration of phenomena surrounding lightning and other static interactions. Students engage with stories and data about lightning and investigate a similar phenomenon in water droppers. They further investigate static interactions with various materials, including sticky tape, digging down to the subatomic level. Students apply these ideas back to lightning and further investigate force interactions, developing Coulomb’s law and ideas about polarization that can be applied to other phenomena. They identify electric fields as the source of the large energy transfers in lightning and explain lightning’s sudden behavior using ionization. They consider why structures made of certain materials provide protection from lightning and investigate why bodies of water, most of which contain dissolved salts, are particularly dangerous during storms. Finally, students develop a consensus model and transfer their understandings to the phenomena of airplane radomes and conducting gels used to simulate brains.

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Additional Unit Information

Building Toward the Following Standards and Practices
Performance Expectations

This unit builds toward these performance expectations:

HS-PS1-1* Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.

HS-PS1-3* Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles. 

HS-PS2-4† Use mathematical representations of Newton’s Law of Gravitation and Coulomb’s Law to describe and predict the gravitational and electrostatic forces between objects.

HS-PS2-6* Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.

HS-PS3-2 Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motion of particles (objects) and energy associated with the relative positions of particles (objects). 

HS-PS3-5† Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction.

*This performance expectation is developed across multiple units. This unit reinforces or works toward these NGSS PEs that students will develop more fully in future units. 

†This performance expectation is developed across multiple courses. This unit reinforces or works toward these NGSS PEs that students will develop further in the OpenSciEd biology and/or physics courses.

Disciplinary Core Ideas

PS1.A: Structure and Properties of Matter 

  • Each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons. (HS-PS1-1)
  • The periodic table orders elements horizontally by the number of protons in the atom’s nucleus and places those with similar chemical properties in columns. The repeating patterns of this table reflect patterns of outer electron states. (HS-PS1-1, HS-PS1-2)
  • The structure and interactions of matter at the bulk scale are determined by electrical forces within and between atoms. (HS-PS1-3, secondary to HS-PS2-6)

PS2.B: Types of Interactions

  • Newton’s law of universal gravitation and Coulomb’s law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects. (HS-PS2-4) 
  • Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space. Magnets or electric currents cause magnetic fields; electric charges or changing magnetic fields cause electric fields. (HS-PS2-4, HS-PS2-5)
  • Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects. (HS-PS2-6, secondary to HS-PS1-1, secondary to HS-PS1-3)

PS3.A: Definitions of Energy 

  • Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system’s total energy is conserved, even as, within the system, energy is continually transferred from one object to another and between its various possible forms. (HS-PS3-1, HS-PS3-2)
  • At the macroscopic scale, energy manifests itself in multiple ways, such as in motion, sound, light, and thermal energy. (HS-PS3-2, HS-PS3-3)
  • These relationships are better understood at the microscopic scale, at which all of the different manifestations of energy can be modeled as a combination of energy associated with the motion of particles and energy associated with the configuration (relative position of the particles). In some cases the relative position energy can be thought of as stored in fields (which mediate interactions between particles). This last concept includes radiation, a phenomenon in which energy stored in fields moves across space. (HS-PS3-2)

PS3.C: Relationship Between Energy and Forces 

  • When two objects interacting through a field change relative position, the energy stored in the field is changed. (HS-PS3-5)
Science & Engineering Practices

Developing and Using Models: This unit intentionally develops students’ engagement in these practice elements:

  • Evaluate merits and limitations of two different models of the same proposed tool, process, mechanism or system in order to select or revise a model that best fits the evidence or design criteria.
  • Design a test of a model to ascertain its reliability.
  • Develop, revise, and/or use a model based on evidence to illustrate and/or predict the relationships between systems or between components of a system.
  • Develop and/or use multiple types of models to provide mechanistic accounts and/or predict phenomena, and move flexibly between model types based on merits and limitations.
  • Develop and/or use a model (including mathematical and computational) to generate data to support explanations, predict phenomena, analyze systems, and/or solve problems.

Obtaining, Evaluating and Communicating Information: This unit intentionally develops students’ engagement in these practice elements:

  • Critically read scientific literature adapted for classroom use to determine the central ideas or conclusions and/or to obtain scientific and/or technical information to summarize complex evidence, concepts, processes, or information presented in a text by paraphrasing them in simpler but still accurate terms.
  • Compare, integrate and evaluate sources of information presented in different media or formats (e.g., visually, quantitatively) as well as in words in order to address a scientific question or solve a problem.
  • Gather, read, and evaluate scientific and/or technical information from multiple authoritative sources, assessing the evidence and usefulness of each source.
  • Evaluate the validity and reliability of and/or synthesize multiple claims, methods, and/or designs that appear in scientific and technical texts or media reports, verifying the data when possible.
  • Communicate scientific and/or technical information or ideas (e.g. about phenomena and/or the process of development and the design and performance of a proposed process or system) in multiple formats (i.e., orally, graphically, textually, mathematically).

The following practices are also key to the sensemaking in this unit:

  • Asking Questions and Defining Problems
  • Planning and Carrying Out Investigations
  • Using Mathematics and Computational Thinking
  • Constructing Explanations and Designing Solutions
  • Engaging in Argument from Evidence
Crosscutting Concepts

Patterns: This unit intentionally develops students’ engagement in these crosscutting concept elements:

  • Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.
  • Mathematical representations are needed to identify some patterns.
  • Empirical evidence is needed to identify patterns.

Scale, Proportion, and Quantity: This unit intentionally develops students’ engagement in these crosscutting concept elements:

  • The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs.
  • Some systems can only be studied indirectly as they are too small, too large, too fast, or too slow to observe directly.
  • Using the concept of orders of magnitude allows one to understand how a model at one scale relates to a model at another scale.
  • Patterns observable at one scale may not be observable or exist at other scales.
  • Algebraic thinking is used to examine scientific data and predict the effect of a change in one variable on another (e.g., linear growth vs. exponential growth).

The following crosscutting concepts are also key to the sensemaking in this unit: 

  • Cause and Effect 
  • Systems and System Models
  • Energy and Matter
  • Structure and Function
Connections to the Nature of Science

Which elements of NOS are developed in the unit?

  • Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena.
    • Theories and laws provide explanations in science.
    • Laws are statements or descriptions of the relationships among observable phenomena.
  • Scientific Knowledge is Based on Empirical Evidence.
    • Science knowledge is based on empirical evidence.
    • Science arguments are strengthened by multiple lines of evidence supporting a single explanation.
  • Scientific Knowledge is Open to Revision in Light of New Evidence.
    • Most scientific knowledge is quite durable but is, in principle, subject to change based on new evidence and/or reinterpretation of existing evidence.


Unit Information
What is the anchoring phenomenon and why was it chosen?

For the anchoring phenomenon, students explore slow motion-videos and data about lightning, as well as stories about lightning, and develop models for what causes it and why certain places are safer than others when it strikes. Exploring lightning allows students to 1) discover the science ideas about the structure and properties of matter and energy, 2) build from the understanding of matter and energy they developed in the prior unit, and 3) make personal connections to a relatively common natural phenomenon.

The lightning anchoring phenomenon was chosen from a group of phenomena aligned with the target performance expectations. The selection was made based on the results of a survey administered to students from across the country and in consultation with external advisory panels that include teachers, subject matter experts, and state science administrators. Lightning was chosen for the following reasons:

  • Teachers and state science administrators saw high relevance to students’ everyday experiences.
  • Explaining the interactions involved in a lightning strike addresses the selected pieces of DCIs in this bundle at a high school level.
  • Students have the opportunity to experience scaled-down versions of lightning systems in the classroom and use it to investigate static interactions.
  • Reflection on lightning safety allows for molecular-level materials exploration and common lightning safety reasoning that is relevant to students’ lives.
How is the unit structured?

The unit is organized into four lesson sets. Lesson Set 1 (Lessons 1-5) supports students in figuring out what lightning through engagement with related static phenomena.. Along the way they develop principles of electrostatics and subatomic structure. Lesson Set 2 (Lessons 6-9) further develops ideas about the electrostatic forces in a cloud and the relationship between the variables in Coulomb’s law. A mid-unit task allows students to apply their understanding to a variety of new related phenomena. Lesson Set 3 (Lessons 10-11) shifts the focus to look at energy transfers within electrostatic fields. Lesson Set 4 (Lessons 12-14) explores why certain materials and places are safer than others when lightning strikes. Students apply these ideas in a transfer task in Lesson 14.

Where does this unit fall within the OpenSciEd Scope and Sequence?

This unit is the second in the OpenSciEd High School Chemistry course sequence. This unit is designed to build on student ideas from Unknown material with identifier: cm about energy flows at the particle level as students use patterns in electrostatics to help explain how lightning works. Along the way, they dig into the atom and develop understandings of subatomic structure, charges, and the ways in which small-scale interactions of matter and energy through forces result in material properties and macroscopic effects.

All the Performance Expectations (PEs) in this unit are shared across other Chemistry or Physics units:

  • HS-PS1-1, HS-PS1-3, and HS-PS2-6 are shared with OpenSciEd Unit C.3: How could we find and use the resources we need to live beyond Earth? (Space Survival Unit)
  • HS-PS2-4 is shared with OpenSciEd Unit P.4: Meteors, Orbits, and Gravity (Meteors Unit)
  • HS-PS3-2 is shared with OpenSciEd Unit C.5: Which fuels should we design our next generation vehicles to use? (Fuels Unit), OpenSciEd Unit P.1: How can we design more reliable systems to meet our communities’ energy needs? (Electricity Unit), and Meteors Unit
  • HS-PS3-5 is shared with Fuels Unit and Electricity Unit

In Space Survival Unit, students will leverage their initial understandings of subatomic structures and bonding to build a deeper understanding of molecular structures, periodic trends, and chemical reactions as they explore human survival in space. Students’ initial ideas about fields similarly build, this time across courses as students quantify energy stored in electric fields between atoms in Fuels Unit, develop their thinking around the practical applications of fields in Electricity Unit, and quantify energy stored in gravitational fields in Meteors Unit. In Meteors Unit, they will also develop Newton’s Universal Law of Gravitation, which is strikingly similar to Coulomb’s Law students construct in this unit.

What modifications will I need to make if this unit is taught out of sequence?

This is the second unit of the High School Chemistry Course in the OpenSciEd Scope and Sequence. Given this placement, modifications would need to be made if teaching chemistry first, or teaching this unit earlier in the Chemistry Course. These include the following adjustments:

  • Only minor modifications would be needed to teach this lesson before OpenSciEd High School Biology. Students may require additional support in the practices and crosscutting concepts that are intentionally developed in this unit if they have not previously had these experiences at the high school level.
  • Unknown material with identifier: cm.n emphasized community-building, including the development of Community Agreements in Lesson 1. If this unit is taught before that one, some supports from that unit should be brought in to help students develop a culture of working together to make progress in science sensemaking.
  • Unknown material with identifier: cm.n also contains significant support to help students develop high school-level investigative planning and techniques, introduce them to mathematics and computational thinking in a chemistry context, and scaffold their thinking around matter and energy in chemistry. If this unit is taught earlier in the year, supplemental teaching of the particle model of matter and energy transfer mechanisms will be required. Students will also require additional instruction in lab safety, conducting investigations, and using unit conversions and scientific notation.
  • If taught after OpenSciEd High School Physics, students will likely already be familiar with the M-E-F triangle and fields and may require less support in sensemaking in Lessons 3-5 and 10-11 in particular.
  • If taught as part of an AP Chemistry course, this unit and Space Survival Unit, which collectively develop student thinking around subatomic structure and compound formation, will need to be supplemented with more in-depth examination of novel Lewis diagrams, resonance, VSEPR and bond hybridization, intermolecular forces, and mass spectroscopy and photoelectron spectroscopy.
  • If taught as part of AP Physics 2, this unit will require significant supplementation in order to better quantify electrical energy, model charge distribution and resulting forces and fields more systematically, and more deeply reflect on conservation of matter (specifically charge) and (electrical) energy, which are assumed but not emphasized in this unit.
  • This unit does not address any Earth and space science standards, as it relies on middle school level understandings of weather. If used in an Earth science course, students will need to engage much more deeply with these standards and may also need to investigate different kinds of lightning and Earth’s global electric circuit.
What mathematics is required to fully access the unit’s learning experiences?

This unit uses mathematics in three main ways:

  1. Students are occasionally asked to use unit conversions and read scientific notation, keeping fresh skills built in Unit C.1 Thermodynamics in Earth’s Systems.
  2. Students gather and represent data in ways that can help them identify patterns in nonlinear graphs, building off of work with linear graphs in Unit C.1 Thermodynamics in Earth’s Systems.
  3. Students carry out calculations with Coulomb’s law, which is a nonlinear equation.

Students engage in this mathematical thinking in Lesson 7 when they describe patterns across nonlinear graphs, evaluate the relationship between the variables in Coulomb’s law, and apply techniques of algebra and functions to solve for the value of one unknown variable in the equation. Students use these mathematical relationships again in Lesson 9 as they complete a mid-unit assessment.

This unit does not assume students are fluent with the mathematical practices listed below that were not developed in Unit C.1 Thermodynamics in Earth’s Systems, but that students develop these practices as part of the sensemaking. Thus these standards are not so much prerequisites, as co-requisites. If students are simultaneously developing the skills and vocabulary in math class, you can help by making explicit connections to the mathematical standards.

How do I shorten or condense the unit if needed? How can I extend the unit if needed?

We recommend allocating time so that the entire course can be taught. Depending on your priorities among physical science standards and supplemental chemistry content, you may condense and focus students on the following parts. If you condense the unit, you will lose important sensemaking for students.

  • Lessons 2-3 can be shortened with students watching the provided videos instead of using the physical water dropper. This will remove an opportunity for them to plan their own investigations to test the reliability of their current models in Lesson 3.
  • Lesson 4 can be shortened by removing an opportunity for peer feedback on models. Similarly, Lesson 9 can be shortened by removing an opportunity for self-assessment.
  • Lesson 7 can be shortened by having each group only investigate one of the four conditions, as long as all four conditions are covered.
  • Lesson 11 can be shortened by having students complete more of the research for home learning, although this is not recommended as it removes their access to peer and teacher supports while they gather information.

To extend or enhance the unit, consider following all lesson extensions.

  • A number of lessons have extension opportunities and alternate activities. See Lessons 1-3, 5, 8-9, and 12-14 for built-in extensions.
  • Spend more time on material properties, building on students’ investigations in Lessons 12 and 13. Although students will have additional opportunities to engage with different materials in Space Survival Unit, they will benefit from investigating the properties of a wider variety of materials and beginning to question why materials made of “different stuff” interact so differently at the macroscopic and microscopic scales.
  • More carefully examine lightning in your own community. Have students use the models they develop in this unit to explain why patterns in your community differ from other places, and how climate change may result in these patterns changing over time.
  • Provide students opportunities to communicate with broader audiences about lightning safety or about other facets of lightning. For example, some students may be interested in phenomena like upper-atmospheric lightning and lightning on other objects in the solar system. Moving students’ attention toward the solar system could be an excellent opportunity to help motivate the beginning of Space Survival Unit.
Unit Acknowledgements
Unit Development Team
  • Dan Voss, Unit Lead, Northwestern University
  • Rachel Patton, Unit Lead, Denver Public Schools
  • Tara McGill, Field Test Unit Lead, Northwestern University
  • Michael Novak, Field Test Unit Lead, Northwestern University
  • Gail Housman, Writer, Northwestern University
  • Kathryn Ribay, Writer, San Jose State University
  • Nicole Vick, Writer, Northwestern University
  • Michelle Zhang, Writer, Oak Park & River Forest HS District 200
  • Kerri Wingert, Coherence Reviewer, University of Colorado Boulder
  • Melissa Campanella, Content Expert, University of Colorado Boulder 
  • Oluwatoyin Olanipekun, Content Expert, University of Wisconsin Madison
Production Team
  • Madison Hammer, Production Manager, University of Colorado Boulder
  • Erin Howe, Project Manager, University of Colorado Boulder
  • Sara Krauskopf, Video Production, University of Colorado Boulder
  • Stephanie Roberts, Copy Editor, Beehive Editing
Unit External Evaluation
NextGenScience’s Science Peer Review Panel

An integral component of OpenSciEd’s development process is external validation of alignment to the Next Generation Science Standards by NextGenScience’s Science Peer Review Panel using the EQuIP Rubric for Science. We are proud that this unit has earned the highest score available and has been awarded the NGSS Design Badge. You can find additional information and read this unit’s review on the nextgenscience.org website.