Periodic Table Trends

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Students will be able to explain the trends for electronegativity, ionization energy, and atomic size on the Periodic Table by performing an activity, taking notes, and doing practice questions.

Big Idea

Ionization energy, electronegativity, and atomic size display characteristic trends on the Periodic Table.


In this lesson students learn about the trends of the Periodic Table by doing an inquiry activity, taking notes, watching videos, and doing practice questions.  Within this unit students already learned about electronegativity in terms of bonding types in lesson 6: Metallic and Covalent Bonds.

  • This lesson aligns with NGSS Performance Expectation: HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
  • This lesson aligns with NGSS Science and Engineering Practice 4: Analyzing and Interpreting Data because students use data to figure out the trends on the Periodic Table.
  • This lesson aligns with NGSS Science and Engineering Crosscutting Concept 1: Patterns because students learn about the patterns of various trends on the Periodic Table.

Within this lesson there are no additional resources needed.


30 minutes

To begin the lesson I have students begin to figure out the trends for ionization energy, electronegativity, and atomic radius through an inquiry activity. 

  1. I start by passing out the Graphing Periodic Trends Activity paper.
  2. I then read the instructions to students highlighting how these three trends are important and that we will discuss in more detail through notes.
  3. I then begin to model how to begin to fill out the trend for atomic radius and go over the trend across periods.  I do this by filling out a paper on the projected document camera so students can see how I choose a color and then write in the information for atomic radius for each of the provided elements.
  4. I have students continue to fill out the paper with the data, then write out the trends down groups and across periods.
  5. As students are working I allow them to work with a partner if they find that easier.  I also walk around to ensure that they are remaining on task and understanding the trends.  I ask questions such as "What happens to atomic radius across periods?"  or "What happens to ionization energy as you go down a group?"
  6. This video explains how I do this in my classroom.
  7. As students are done I make sure that they have the correct trends.  This is the answer key for expected answers.


30 minutes

In this section of the lesson I go through the trends with students.  My goal is for students to learn what the trends are but also understand why the trends occur.

The lesson begins on slide 6 of the PowerPoint and students fill in their notes graphic organizer while I present the information.

I begin the lesson by going over effective nuclear charge (slides 6-9) as this is an important aspect of the trends.  To use an analogy I talk about Tommy the Trojan (our school mascot) and how his charm is the effective nuclear charge with those students closest to him being most effected by his charm.  I also use the analogy of students in a classroom and those closest to the teacher are watched more closely.

I then go into the three major trends for atomic radius, ionization energy, and electronegativity with students filling out information in a table on their graphic organizer.  

For each trend....

  1. I give a definition
  2. I show students the data and have them tell me the trend that they see/found in the intro activity.  For example for atomic size on slide 11 students will say that size decreases across periods and increases down groups.
  3. I go over the trends down groups and across periods with the rationale.
  4. I show students a video for each trend which I embed in the PowerPoint and are found below...
  • Periodic Trends: Atomic Radii

  • Periodic Trends: Ionization Energies

  • Periodic Trends: Electronegativity


This is a copy of the filled in notes that are expected from students.


60 minutes

To reinforce the trends I have students perform a practice worksheet.  The worksheet contains two sections. 

1. For the first section students explain characteristics of the trends on the periodic table.

This year I decided to have students do the first section of the worksheet with partners.  I did this because I could tell that after doing the trends activity and notes that students needed to get up and move around a bit. 

Because I did not initially make the worksheet as a partner practice paper I had students write 1-4 at the top of their paper and find partners.  I then assigned them questions to work on with their partners.  For additional information on how I use partner appointments in my classroom please look at the Partner Appointments reflection in Unit 1 Lesson 7: Dimensional Analysis.

The questions for trends are tricky and a lot of students want to just right the trend, but not explain why the trend occurs.  To help students I continuously remind them to look back at their notes for help with the rationale for the trend.

This is a copy of the answer key for the first section with how I added in partner appointments at the top and the questions I had students perform with their partners.


2. For the second section of the worksheet students first fill in various elements on a blank periodic table and then compare the various elements to each other using the trends. 

After doing the partner practice on the first section students find the second part easier, and I encourage them to try the questions on their own first and then ask their table partners or myself for help if they are stuck. 

If students do not complete the second half I have them complete for homework.  I then stamp the homework for completion during the following class and go over the answers using the answer key.

The most common mistakes that students made on these worksheets was not explaining why the trend occurs.  For example on the second worksheet for question letter e, some students would just write that Cesium has the lowest ionization energy because it is at the bottom left of the Periodic Table, and not explain that the ionization energy is so low because the atom is so big that the outermost electron is very far from the nucleus and thus requires less energy to remove than does the outermost electron in a smaller atom.