Introduction to covalent bonding
Lesson 8 of 12
Objective: SWBAT predict the number and types of bonds (i.e. covalent, ionic) formed based on elements' outermost electrons and position on periodic table.
This lesson is similar to many of the lessons that I do where students take interactive notes to learn a concept. Prior to this lesson students have learned that elements can gain or lose electrons to bond. In this lesson my students will learn how elements covalently bond by showing that elements can share electrons.
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.
This lesson continues with the Science and Engineering Practice (SEP)2: Developing and using models by having student use Lewis dot diagrams to illustrate that atoms such as hydrogen and oxygen can share electrons to obtain an octet.
For this lesson I do not collect or check in this homework assignment. My students are aware of my collecting of homework and check-in process, and realize that I randomly give credit for homework. I created this policy because homework is meant for practice to learn the content and prepare for the test, not inflate ones grade percentage. I discuss my philosophy about homework further in my lesson reflection.
At the beginning of class I will ask students if they have any questions about ionic bonding and the ionic basics homework. To get the ball rolling, I put the assignment on the document camera and start by briefly going over one problem at a time. My main objective is to make sure that students have the correct answers so they can study the correct information, and realize that arrows are used to show the transfer of electrons to obtain an octet.
Going over the homework also acts a good platform for showing the difference between ionic and covalent bonding. At this point my students have been informed that covalent bonding is the sharing of electrons between nonmetals, but do not understand why, or how, sharing of electrons is different from the transfer of electrons.
This is one of the few times that I use a PowerPoint to explain a concept. I use one during this lesson because showing them how electrons can be shared through a frame by frame (slide) breakdown helps them visualize the process.
The Powerpoint has about 50 slides, many of which act as a frame by frame that shows the movement of electrons. Since this is a long PowerPoint that only has portions of information that needs to be copied, I give a Note Outline that helps them follow along. This allows me to work through the ppt. in 10-15 minutes.
The beginning of the Powerpoint starts with a brief review of ionic bonding, but quickly gets into what a covalent bond is. The covalent bonding portion starts by showing students how Cl and Cl bond when they come in contact with one another to share unpaired electrons. This is followed by showing oxygen bonding to another oxygen with a double bond with two bonding pairs of electrons.
The notes end with a summary of ionic, covalent and metallic bonds. Even though I do not cover metallic bonding, I do summarize it because many students ask about it throughout the unit due to curiosity.
In this part of the lesson we work on covalent bonding step by step, the process of making covalent bonds using Lewis dot structures. First I reviewing Lewis dot diagrams and then how to determine how many unpaired electrons are present. For example, nitrogen has 3 unpaired electrons and can form three bonds. At this point it hasn't been determined which type of bond will form, just that there will be three bonds.
Now that they've established the number of bonds for the elements being used in this activity and determined the number of bonds, I show them how to do the first molecule, nitrogen bonded to hydrogen. The finished molecule will be NH3 with three single bonds and one non-bonded pair of electrons which can be seen in the guided notes demonstration.
The process of going over all the guided notes takes the majority of class time, so there is very little time for a formal assessment. So as they work the problems I share my time with the seven lab tables (groups) that typically work on problems together.
My students understand that there are 28 of them and that I can’t always split my time evenly among them. When it comes to guided practice, I encourage them to work together as a group so that they can maximize learning. The groups are based on who their lab partner is which was determined by academic strength (usually an A, 2 B/C and 1 D/F student). This classroom procedure has benefited many students and allows me to focus my attention on the individuals that need one-on-one help.
Since we move through bonding at a relatively fast pace, I give them a covalent homework assignment that provides reinforcement before moving on to periodic trends. The homework is a summary of valence electrons, drawing Lewis dot diagrams and showing sharing of electrons with bonding pairs of electrons.
The next class period will be devoted to going over the guided practice, homework and reviewing the necessary concepts on covalent bonding.