We're going to be honest: we do Physics. That's why this is called The Physics Classroom website. And when we do the Teacher's Notes section for our Concept Builders, we typically have a lot to say ... and a lot of resources to point you to. We're not claiming to be ignorant of chemistry; we just don't have a lot of resources here at The Physics Classroom to point you to. And so this page is going to be a lot shorter than our usual page that accompanies our Physics Concept Builders. That's our honest confession.

Chemistry courses that devote time to a discussion of covalent bonding usually accompany that discussion by the construction of Lewis electron dot structures. Most of that discussion is devoted to the drawing of Lewis Structures. The drawing of a Lewis Structure involves counting the number of valence electrons, creating the skeleton structure, and adding dots in pairs around all non-hydrogen atoms until each atom is surrrounded by 8 electrons. Then the student is instructed to inspect their diagram to insure 1) that every atom follows the octet rule (for hydrogen, its the duet rule), and 2) the number of electrons in the diagram is equal to the number of valence electrons. It is this last inspection step that determines whether or not the diagram is correct as initially wirtten or whether it needs to be adjusted. It is also this last step that students have trouble with. And so this Concept Builder provides students with practice counting valence electrons and inspecting already-drawn Lewis Structure diagrams to insure that they are correct.

This Concept Builder consists of three separate activities. The first activity - Counting Valance Electrons - presents students with a formula of a molecular compound and asks them to determine the number of valence electrons. Using a Periodic Table, they determine the number of valence electrons and enter their answer into the provided answer field. Entry can be done using the native keyboard of the device or by tapping on the number pad iocn and using the built-in number pad (recommended for mobile devices). There are six Question Groups in this activity with two questions per group. If students miss a question, they will be presented the same question a second time along with the other question in the group. 

The second activity - Master Configurator - has six Question Groups with three questions per group. Each question presents students with three chemical formulae for molecular compounds and a corresponding Lewis Structure. Students must inspect each Lewis Structure to determine if it is correct. Students must identify all those structures which are incorrect. Incorrect structures include two common problems - the number of electrons in the diagram are not equal to the number of valence electrons or one or more of the atoms (of period 2 elements) break the octet rule. One of the Question Groups includes a boron-containing molecule so it may be important to notify students in advance of boron's tendency to acquire only six electrons through covalent bonding. This is discussed in the help pages that accompany every question.

The third activity - Electron Dot Wizard - is similar to the second activity except for the fact that every question includes one or more ions. It also includes numerous instances like PCl₅, SF₆, and XeF₄ in which the central atom exceeds the Octet Rule. Each of these exception types are discussed in the Help pages that accompany every question. Like the second activity, students must make it a habit to count valence electrons that should be present and that are present in the diagram. They must also make sure that Period 2 elements satisfy the octet rule. There will be many instances in which the Lewis Structure is correct but the central atom exceeds the octet rule. In all such legitimate exceptions to the Octet Rule, the central atom is a Row 3 or lower element. For certain, this third activity is indeed difficult and should be previewed by teachers before assigning it to students. The Octet Rule exceptions are the most difficult part ... especially for oxyanions. An exposure or even comfort with the concept of formal charge will assist students with this third activity.

Like all our Concept Builders, this Concept Builder utilizes a variety of strategies to make each student's experience different. The ordering of questions is random. The Question number assigned to each question is scrambled. For instance, two side-by-side students will not have the same question for question number three. And questions are organized into Question Groups with questions within the same group being very similar (for instance, they have the same type of information as "givens") but not identical. 

The Concept Builder also keeps track of student progress. It requires that students demonstrate a mastery of questions in each Question Group. If they miss a question from one group, then they will have to answer two consecutive questions correctly in order to demonstrate mastery. Progress is displayed in the progress report on the right side of the Concept Builder. 

In order to complete an activity, a student must correctly analyze each question of that activity. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar question twice in order to successfully complete the activity. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through an activity, a system of stars and other indicators are used to indicate progress on the activity. A star is an indicator of correctly analyzing the question. Once a star is earned, that question is removed from the que of questions to be analyzed. Each situation is color-coded with either a yellow or a red box. A red box indicates that the student has incorrectly analyzed the question and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the question must be correctly analyzed one time in order to earn a star. Once every question of a difficulty level has been analyzed, the student earns a Trophy which is displayed on the Main Menu. This system of stars and trophies allows a teacher to easily check-off student progress or offer credit for completing assigned activities.

The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each question group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise.