Bohr-Rutherford Modeling

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Objective

SWBAT interpret the information present from the periodic table to draw Bohr-Rutherford models of the atom with correct arrangements of particles.

Big Idea

Applying the information and patterns on the periodic table to atomic structure.

Background

This lesson continues to address 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.  Students are using their understanding of the information on the periodic table to generate Bohr-Rutherford Models of the Main Group Elements (groups 1-2, 13-18).  By generating their own models, we access Science and Engineering Practice 2: Developing and Using Models.

After creating their models, students are seeking Patterns (Cross Cutting Concept 1).  Here their models are serving as our empirical evidence to identify patterns.  This is the first time we have been able to access the Patterns CCC at the high school level.

My students continue to struggle with visualizing the atom and its structure.  By continuing to draw the models, we practice the skill of modeling accurately while helping to practice and ingrain the structure of the atom.  Students will deduce patterns from their models, making the jump from individual atoms to patterns of the periodic table.

This lesson is delivered in a 42 minute period, due to my district using a shortened schedule once per week to allow building meetings.

After I did this lesson, one of my colleagues did it similarly, but printed the chart on 11"x17" paper.  This provided the students more room to work, and by virtue of being larger and different, impressed upon them the importance of understanding the patterns in atomic structure as they are found in the periodic table.  I look forward to using her modification next year.

Opener -- Review

5 minutes

When students walk in, I have placed their Bohr-Rutherford papers on their tables.  I ask students to get out their periodic table, and put their names on the new paper.

While students are getting organized, I take attendance and project a copy of the worksheet on the overhead.  I zoom into a fourth period element to show all four electron shells.

Once students are ready, I ask them "Who remembers how many electrons fit on the first energy level?" and get the response of "2."  I repeat this for the next three energy levels and get the responses of "8" "8" and "18."  If students ask how we remember that, I deflect the question to someone who answered it.  They should refer back to unit 1 when we did our Build An Atom or Drawing the Atom lessons.

I point out the reminders of how many electrons fit on each level at the top of the page and direct the students to group 1, period 3, where we will do the example for sodium together.

Whole Group Practice

7 minutes

Students are still getting used to using the periodic table, so I use the overhead to demonstrate how to make our model for Sodium.  This allows students to know what an acceptable model looks like, and provides the target to achieve on the rest of their models.

I then allow students to split up the elements as a table, with each student doing four elements at a minimum and share.

Individual Practice

18 minutes

While students are working, I am circulating the room, checking their work, and answering questions.  Most important during this time is to provide some positive feedback for students who are completing their models accurately as student confidence is still low.

The most common question that arises is "How do I know how many electrons go on each ring?"  I refer them back to the instructions on the top of the worksheet, and verbally have them repeat the maximums for each level.

One error students make in solving for neutrons is incorrectly rounding the atomic mass from the periodic table.  I check that as I go, as it is a sign of very low math skills.  After class, I write down the names of students I notice making this error so that I can keep an eye on them later in the semester when we do more math-related concepts.

As students are wrapping up, I direct them to the three questions about the patterns they see.  I allow students to engage these questions as a table, to talk out what they are observing.  These patterns are the reason behind the modeling activity, and are the crucial concepts for this lesson.  Many students expect these to be difficult, and struggle with the visual and numerical patterns.

Desired responses to the final questions are:

  • Q1- Explain the pattern between the group number and the number of valence electrons
  • A1: The number of valence electrons is the same as the ones place (or last digit) of the group number.
  • Q2- Explain the pattern between the period number and the number of electron shells/levels
  • A2: The period number is the same as the number of electron levels.
  • Q3- Explain the pattern between the maximum number of electrons in each outer shell and the number of elements in that period.
  • A3: The maximum number of electrons in the outer shell is how many elements are in that period.  (e.g. shell 3 holds 8 electrons and there are eight elements in period 3)

When time is up, I ask students to turn in their models, and to prepare for our quiz.

Quiz

12 minutes

I pass out the Periodic Table and Particles Quiz, ensuring that there is one of each version at each table.  Students use their periodic table to complete the quiz.  I point out that the last three questions are extra credit, and that if they have time, they should at least attempt them.

When students finish, they bring the quiz to the front of the room and turn it in face down on the teacher desk.  If students do not finish by the bell, I have them turn in their quiz as far as they got.

Overall, my four classes averaged a 12/15 on this quiz.  If my gradebook could display median, I believe it would have been a 13 or better.  Most students did exceptionally well, with a few students (including a 1/15) drawing down the average.  Where students did struggle, it was with the number of neutrons, with students choosing to use the atomic number rather than subtract it from the mass number.

One change I've made to my practice this year is quizzing at the end of the period.  While the time constraint can be intimidating to some students, I have had students deliberately dawdle on the quizzes to waste class time.  A 13 question quiz can become a 25 minute affair if given at the start of the period.

The one area I have to be careful of with this practice is accommodating students with IEPs who are not to be timed for assessments.  For these students, I consult them one on one and ask if they are comfortable with the time limit.  If they are not, I give the quiz to their resource teacher, and they take it during their resource period instead. 

Often I coach these to attempt it under the time constraints, and offer them the chance to take a different version in resource if they do not finish.  This allows them to be treated like the rest of the class outwardly, and to work at building a skill they will need beyond high school.