Billion Oyster Project

Get to Know a Few Nitrogen Molecules


Unit

Nitrogen Cycle Investigation

Grade

6-8th

Class Periods

1

Setting

Classroom

Subject Areas

Science


Summary

Students examine multiple meanings of the word line.  Students then build molecular models of an ammonia molecule, a nitrite ion, a nitrate ion, and a nitrogen gas molecule.  They use their molecular models and their practice with multiple meanings to help them understand how the word nitrogen sometimes refers to one part of each of these molecules (nitrogen as a type of atom), and sometimes refers to a whole category of molecules (nitrogen as the category of all the different kinds of molecules that contain nitrogen atoms).

Objectives

  • Identify molecular models of ammonia, nitrite, nitrate, and nitrogen gas.

  • Distinguish between the multiple meanings of a single word.

  • Evaluate the decision to use a more specific or a more general label (e.g. ammonia vs. nitrogen to refer to the same thing).

Materials and Resources

Supplies

  • Molecular model kits or materials for DIY molecular models.  You need enough for each group to use at least:

    • 5 blues (such as gumdrops) to represent nitrogen atoms

    • 3 or 4 whites (such as gumdrops) to represent hydrogen atoms

    • 5 reds (such as gumdrops) to represent oxygen atoms

    • 11 connectors (such as toothpicks)

    • Note: you also need your own set of molecular models.  They can be the same as your students’.

  • Paper and pencil for sketching

  • Paper and markers for labeling the molecular models

  • Optional: a much larger set of molecular models of ammonia, nitrite, nitrate, and nitrogen gas, large enough for everyone to see at the same time -- to refer to during discussions.  This can also serve as the teacher’s set of models.

Before you get started

Tips for Teachers

Be sure to use the recommended colors of gumdrops, because students will encounter them again in chemistry in high school.  Blue is always nitrogen.  Red is always oxygen.  White is always hydrogen.

Preparation

Ideally, prepare a list of students’ questions from the previous lesson, in which they examined and played with test strips for ammonia, nitrites, and nitrates.  (See “Engage” section, below).

Instruction Plan

Engage

  1. Ideally, use your students’ own questions from the previous lesson to motivate this lesson.  One great way to do that is to prepare a list of the questions that they asked while studying ammonia, nitrite, and nitrate test strips, and to ask them to identify any questions that contain the words:
    • Ammonia or ammonium (in this context and at this grade level, it is appropriate to use these two words interchangeably.  When students study chemistry in more depth, they will study the difference between those two substances!  In water, the distinction is especially hard to draw, because ammonia molecules constantly and spontaneously turn into ammonium ions, and vice versa.)

    • Nitrite

    • Nitrate

    • Nitrogen

    • Nitrogen gas
  2. Students see four different ways that people use the word line:
    • “The line of students moved quickly down the hall.”

    • “My fishing line got tangled.”

    • “Write your name on the first line of the page.”

    • “Would you please hold?  My mother is calling me on the other line.”
  3. Individually, students sketch what they think the word line means in each sentence.
  4. In small groups, students compare and contrast the four different uses of the word line.  Do they think some are more alike than others?  Do they think some are exactly the same?  Encourage differing interpretations.
  5. A few groups to report to the full class on the most interesting issues and disagreements from their discussions.

Explore

  1. Each group of students gets a set of blue, white, and red balls from a molecular model kit or gumdrops, plus connectors.

  2. Students get the information that in this model system:

    • Nitrogen atom = blue ball or gumdrop

    • Hydrogen atom = white ball or gumdrop

    • Oxygen atom = red ball or gumdrop

    • Note: If they’re using a molecular model kit, they should probably ignore any extra holes in any of the colored balls

  3. Explain: In this model system, when you connect two or more model atoms, you are making a model molecule.

  4. Explain: Even if they are made up of the same atoms, different molecules have different properties.  A good example is nitrites and nitrates.  The tilapia in the previous lesson were killed by nitrites, but they would still be alive if they were exposed to the same level of nitrates instead.

  5. Each group accesses the images in the powerpoint: Ammonia, Nitrite, Nitrate, and Nitrogen Gas powerpoint.  See images below.

  6. Each group builds its own set of molecular models of:

      • Ammonia or ammonium

      • Nitrite

      • Nitrate

      • Nitrogen gas


    An ammonia molecule and/or ammonium ion:


    A nitrite ion:


    A nitrate ion:


    A molecule of nitrogen gas:


    (That’s a triple bond between the two nitrogen atoms.)



Explain

  1. Explain: “Ammonia/ammonium, nitrite, nitrate, and nitrogen gas are all sometimes called ‘forms of nitrogen’.  There are some good reasons for doing that, but there are also some problems.

    • What do you think people mean when they refer to all four of these different things as ‘forms of nitrogen’?”

  2. Explain: Sometimes people use just the word nitrogen to mean:

    • All ‘forms of nitrogen’ (which in our model system are any sets of connected balls/gumdrops, as long as at least one of them is blue)

    • Just the nitrogen atoms (which in our model system are the blue balls/gumdrops)

    • Nitrogen gas (which in our model system is the pair of blue balls/gumdrops, linked to each other three times)

    • Maybe a few other things as well!

Elaborate

Ask your students discussion questions like:

  1. Why do you think people use the same word to mean different things?  

    • How are the different meanings related to each other?  

    • Do you think they have to be related to each other?  

  2. Can you think of other words that have different meanings?  

    • Are some of the different meanings completely unrelated?

Evaluate

  1. Students label their molecular models.

  2. Maybe some groups will label all of their models “nitrogen.”  Maybe some groups will label each model distinctly.

      • If that happens, point out that both are correct, according to today’s lesson, and ask your students: “what are the pros and cons of labeling all of the models nitrogen?  What are the pros and cons of labeling each model distinctly?

      • If all groups name their models distinctly, label all of your models nitrogen, and ask your students: “Is this also correct?  How does it change the way people will think about my models?”

Standards

NGSS - Cross-Cutting Concepts

  • Energy and Matter

    • Matter is conserved because atoms are conserved in physical and chemical processes.

NGSS - Disciplinary Core Ideas

  • ESS2.A: Earth’s Materials and Systems

    • All Earth processes are the result of energy flowing and matter cycling within and among the planet’s systems. This energy is derived from the sun and Earth’s hot interior. The energy that flows and matter that cycles produce chemical and physical changes in Earth’s materials and living organisms.
  • LS2.B: Cycle of Matter and Energy Transfer in Ecosystems

    • Food webs are models that demonstrate how matter and energy is transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem. Transfers of matter into and out of the physical environment occur at every level. Decomposers recycle nutrients from dead plant or animal matter back to the soil in terrestrial environments or to the water in aquatic environments. The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem.

NYC Science Scope & Sequence - Units

  • Grade 6, Unit 4

    • Interdependence

NYS Science Standards - Major Understandings

    • Matter is transferred from one organism to another and between organisms and their physical environment. Water, nitrogen, carbon dioxide, and oxygen are examples of substances cycled between the living and nonliving environment.