Ionic Bonding With Lewis Dot Diagrams

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Objective

SWBAT predict the number and types of bonds(i.e. covalent, ionic) formed based on elements' outermost electrons and position on periodic table

Big Idea

Ionic bonding can be represented using Lewis dot diagrams.

Introduction

Prior to this lesson my students were introduced to ionic bonding using an ExploreLearning Gizmo.   In this lesson my students continue to learn ionic bonding, this time by modeling the process using Lewis dot diagrams.  Lewis dot diagrams will continue to be useful throughout the unit, and the semester. as students are introduced to covalent bonding and continue to recognize periodicity in whether atoms gain, lose or share electrons to form bonds.  Although only a underlying theme, this lesson build on their knowledge of chemistry as they continue to develop an understanding that Patterns exist throughout many concepts in science, including the periodic table, ion formation and bonding.  

This lesson is aligned with 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" and aligned with 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.

As a continuing theme throughout this unit my students continue to engage in the Science and Engineering Practice (SEP): Developing and using models.  During this lesson my students start to see the purpose of drawing Lewis dot diagrams of metals and nonmetal by showing the transfer of electrons. This helps to enhance students' understanding of the usefulness of modeling in chemistry.  

Quiz/Independent Reading

20 minutes

After the bell rings I get students prepared to take a quiz (quiz key) on the periodic table, ions and Hunting the Elements video by putting a divider between them and another student (see reflection for more info on my quiz procedures).   Once situated, I pass the quiz out and instruct them to turn it in when they are done and pick up the ionic bonding packet, read the passage on ionic bonding and answer questions 1-6.

This quiz is only valued at 15 points (student work).  Its primary purpose is to provide students with a understanding of the basics needed to understand bonding.  If they can determine valence and ionic charge they should have a good foundation for bonding. Most students did well on this quiz with a class average 80%.  I felt confident in moving forward because the main concept of metals losing electrons, nonmetals gaining electrons, groups showing valence electrons and period representing energy levels was understood. 

Most students take less than 10 minutes to take the quiz which leaves plenty of time (10 min) for them to read the passage and answer questions 1-6 in the ionic bonding packet.  After about 20 minutes, I call on random students to provide answers to the questions in preparation for the Guided Practice portion of the lesson.

The purpose of the reading assignment is to provide students with a brief summary about ionic bond characteristics and introduction to the term anion and cation.

I don’t formally assess them on this information because it’s not specifically part of my school curriculum.  However, I do find it useful that they are exposed to this information because it can provide them with better insight into ionic compounds and some of their properties.


Guided Practice

25 minutes

This part of the lesson guides students through the process of drawing Lewis dot diagrams using arrows to show the transfer of electrons from a metal to a nonmetal.  I start this portion by showing them how to diagram Na3N and then asking them to try #1, NaCl, on their own(demonstration video).  As they are working on NaCl I am walking around checking for accuracy on Lewis dot diagrams and arrows showing correct movement. 

After a couple of minutes, I go over it so they can correct errors, followed by completing problem #2, BaO.  I continue this process till all 8 problems are completed (ionic boding answer key).

As a teaching strategy to help struggling students, I encourage kids to help one another and learn from each other.  The key strategy is that all students actually do all 8 problems and not wait for me to give them the answer.  I find that walking around and giving reminders to try it first encourages most students to complete the problems before being given the answers.

I don’t collect this assignment since it is guided practice; it serves as notes for the students will use throughout the unit. 

Evaluate

10 minutes

After completing the guided practice, I tell students to put away their “guide notes” and grab a white board.  For the next five minutes I give them a series of ionic bonding problems starting with an easy one and progressing toward more complex ones.

  1. LiF
  2. MgO
  3. Na2O
  4. AlCl3

Using white boards is an easy way to assess students.  I simply write the problem on the board, give them a minute to write their answer (telling them to keep it turned over till instructed) and having them all hold up their board at the same time.  I do it this way because I can make a quick scan of the room and decide who is struggling and if a certain problem needs to be addresses.  When all boards are raised I write the answer on the board.

The problems that students struggle with the most is when more than one metal is needed to donate an electron to a nonmetal, such as Na2O. At this point I will pull students that struggle aside and ask them to seek extra help after or before school.

These four problems don’t take long and gives me a good idea of student understanding.  After completing the white board assessment, I hand out the homework assignment and briefly explain the homework is more like the previous day's assignment (ExploreLearning) where they will be given a list of elements and have to determine the number of valence electrons, whether they gain or lose electrons to achieve an octet and what type of ion they become.

The second part of the assignment they are given a metal and nonmetal and have to draw the Lewis dot diagram and figure out the formula.  For example, draw the Lewis dot diagram for potassium + oxygen and write the chemical formula.  See the key for example. 

This activity is the last assignment they receive on ionic bonding which summarizes everything they have learned about ions and ionic bonding.  I will check student work  the following day at the beginning of class for accuracy.