This lesson introduces the final trend that will be covered in this unit, metal reactivity. Students will use the Science and Engineering Practices (SEP), Constructing explanations, to understand reactivity of metals. During this lessons students will make observations based on physical properties and reactivity of four Alkali and Alkaline Earth Metals. This information will be used to help students create an understanding of how reactivity of metals increases moving down the periodic table and decrease moving from right to left across a period.
This lesson is aligned with NGSS 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. 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.
This lesson continues to engage students in the Crosscutting Concept Patterns as they see the trends in metal reactivity as they appear on the periodic table. This lesson also provides a brief introduction to chemical reactions.
There is a list of materials that are needed for this lesson that are listed in the Explore/Explain portion of the lesson.
This class starts with a bell ringer that has students answer the following questions about periodic trends:
Normally I have them answer bell ringers in their journals, but I want to give them immediate feedback by grading it in class so I have them answer on a sheet of notebook paper. I chose this form of a formative assessment because students struggle with periodic trends and the more immediate the feedback, the better they can assess there own learning.
After a couple minutes, I instruct students to pass their sheet to the person next to them with the grader write their name on the bottom. Having them sign the bottom is meant to discourage students grading their own.
I then provide the answers to the questions, each being worth 2 points, and have them pass it back to the owner when grading is completed. After they are done looking at their problems I collect them to put in the grade book.
This type of assessment offers students quick feedback and gives me a snapshot of understanding before moving to another topic.
The class overall did well on question one because the answers were located in one row. Questions 2 and 3 were difficult because the answers required them to assess the trend both across a period and in a family.
I chose more difficult questions for 2 and 3 because it correlates with what they will be assessed on during the activity. In the activity students will have to decide what Alkali Metal and Alkaline Earth Metals are most reactive both in the family and across a period.
While students were working on their problems I handed out the Period trends demo sheet. I let them know that I will be conducting a series of demonstrations to illustrate our last trend which is reactivity of metals.
After completing the demonstration I instruct students to answer conclusion questions 1-4 before we move on. These questions summarize the reactivity of metals and should be discussed briefly for understanding. The key objective is to make sure that all students understand that reactivity increase moving down a group and decreases moving across a period.
This is where I have students summarize what they have learned and predict what will happen when potassium is added to water.
After completing this students have a better understanding of reactivity because they now have seen three Alkali metals react. The potassium video demonstration will help them answer the analysis questions on the activity sheet. They should be able to see that Alkali metals become more reactive going moving down the family.
The final part of this activity is to answer the Critical Thinking Question 1-5. I count this as a lab, even though I did it as a demo, so I tell students to make sure that it's thoroughly completed. It will be due the following day.
As class is ending I tell students that they will be quizzed on all the trends, the Periodic table and bonding. This quiz comes a couple of days before the test which acts as a practice test for the students.
Sometimes I will give students a shorter version of the test the day before a test. This allows students to see what they know and what they don’t know. It is a very effective strategy in motivating students to study for a test.