Are you as Clever as Mendeleev?

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Objective

TSWBAT explain an element’s placement on the periodic table in terms of its number of protons and arrangement of outer electrons

Big Idea

How was the periodic table created? Let pretend we were Mendeleev and find out!

Introduction

This lesson addresses the NGSS 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".  The goal of the lesson is for students to model patterns in the periodic table using an activity that simulates what Mendeleev and other scientist experienced in developing the periodic table.  This is aligned with the NGSS Disciplinary Core Idea (DCI) PS1.A: 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.

In this lesson students explore the periodic table using NGSS Science Practice 2  Developing and using models.  The activity has students arrange a set of images (models) based on their identifiable characteristics and similarities.  Arranging the images will lead to idea that the periodic table show that elements arranged in columns and rows display Patterns (an NGSS Crosscutting Concept) in their physical and chemical properties.  

Engage

10 minutes

As students walk into class I instruct them to answer the question on the board in their science journal.  What are two examples of categorization that have made your life easier?

After a couple of minutes I ask for student volunteers to provide some examples.  Responses will vary a great deal, but some of my favorites and most applicable to the periodic table are computer files, closets (shirts, pants, shoes) and grocery stores. 

I like to focus on the grocery stores because the group conversation is easily directed towards the various sections within the store and how each section, such as dairy, are even categorized further into subcategories .  This generates a lot of conversation about patterns and categorization.

I then ask the question, "are all grocery stores laid out the same way?"  Followed by, "is the produce section located in the same place in all grocery stores?"  

Most students respond with "no", which is a good transition into the periodic table and how it is categorized and predictable.

I continue questioning by asking: "how is the periodic table arranged?"  A typical student response is "by atomic number." 

I conclude this part of the lesson by asking, "are there any other ways it is arranged that can provide important information?

Some students remember that periods represent the number of electron shells (or size of the atom) and groups have something to do with outer electrons. 

Students say outer electrons because valence is still a new term that is still unknown for many students.

Explore

30 minutes

The activity for the day has students arrange a series of characters in a pattern using several organizing characteristics:  body shape, number of hair stands, body type, number of arms, and facial features.  The purpose of this activity is to get students to think about the periodic table and how it has a complex set of patterns that are predictable.

I start the activity by passing out a copy of the activity sheet and explain to my students that they will be working in groups of two or three with the person(s) next to them.  

I then read the instructions and explain that there are three clues that will guide them in their quest.  The 1st clue explains that there are different ways to arrange the series of individuals.  I use the number line in the activity as an analogy.  The 2nd clue is that unlike the table of numbers, the columns and rows of species do not have to have the same number of pictures. The 3rd and most important clue is there will be three rows when you are finished. The rows do not have the same number of sketches in each row.

At this point I hand each group a sheet of species and have them cut out the characters.  Having them cut out the images saves me prep time, but I tell my students know that this is not art class and it should only take a couple of minutes to perform this task seeing how there will only be 20 minutes to complete the task.

Prior to handing out the sheet of species I black out one of the images with a marker so that they have to draw the missing species based on  the similar characteristic of the other images.  After I hand out the sheet of species I explain that there is a missing character that will need to be sketched on their activity answer sheet.

Getting students to model their thoughts is sometimes difficult, so while they are working I walk around asking what there thought process is (here is a sample student video) and encourage struggling students to start by organizing the images into 3 groups based on a set of defining characteristics such as, number of arms.  This typically points them in the right direction. 

As I walk around I tell each group to call me over when they are finished so I can check for accuracy.  This usually takes several times. Once completed they are instructed to answer the questions on the activity sheet.

Elaborate

10 minutes

After students have correctly arranged the pictures they should take a picture of the correct arrangement, then make some observations about body features based on rows and columns.

After their pictures are arranged they can begin to answers the questions on the Mendeleev answer sheet.  The way students’ answer these questions varies quite a bit, but should generally state trends that are occurring such as 3 arms on all images in row three and 2 stands of hair in all images in column 2 (Mendeleev answer key).  

Evaluate/Homework

10 minutes

The evaluation portion of the activity is the species answer sheet. Since students finish this activity at various times this may be homework for several groups of students.

Towards the end of the class I tell all students to take a picture of completed arrangement so that they can answer the questions at home (species answer key).  If students do not have a camera they may glue the images to a sheet of paper.

Some of these questions are difficult for students because they are still learning the periodic table. However, I still have them answer the questions because I sometimes use this activity to scaffold future information about valence electrons. So if students cannot answer questions 6 and 7 I do not penalize them.