This lesson is aligned with NGSS HS-PS1-2, "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.
In this lesson my students are introduced to covalent and ionic bonding by determining if a compound is formed by a metal and a nonmetal bonding, or a nonmetal and another nonmetal. They are also introduced to Lewis dot diagrams and the concept of gaining and losing electrons.
Students use the periodic table to engage in the Science and Engineering Practice (SEP): Developing and using models. Modeling occurs in this lesson as students take a blank periodic table with a list of ionic and covalent chemical formulas and places each element in the formula in its appropriate place on the periodic table . This process helps them create a model that illustrates the basic idea of what is needed for each type of bond.
I start class by showing Brainpop: Chemical Formulas. I show this to introduce the concept that different elements can gain, lose or share electrons to form chemical bonds. This is a short 4:30 minute video that does a great job of reviewing the parts of the atom and introducing electrostatic attraction. I also like that it talks about molecules being “sticky”, a term that I use frequently to describe the properties of ions and compounds. I also use "sticky" during IMFs which is the next unit after bonding.
Brainpop is an excellent resource that has a variety of science related topics which are narrated by two cartoon characters, Tim and Moby (a robot that uses nonverbal communication). Most of the videos are 3-5 minutes in length and come with printable quizzes and activities. I typically will use the videos as introductions, but they are extremely effective as a short review too.
Overall kids like them, and they can generate a decent classroom conversation on key variety of concepts. The one caveat is that it does require a membership fee of about seven dollars per month, but I find the fee completely worth the price. As an alternative to the video, I have attached a link to a YouTube video that uses a song to describe the different types of bonding.
After the video, I do not give them the quiz that the Brainpop website provides, but instead engage in a brief discussion about what the video was about. By discussing the video instead of quizzing, a student-centered curiosity about how chemical bonding is developed which can scaffold further learning.
Most of the conversation focuses on the idea that molecules are sticky (because Tim makes a joke) and that atoms can lose or gain electrons to become stable. This concept is difficult for students to grasp because they have just learned that the number of protons and electrons are equal which make atoms neutral. However, as we progress through the unit they usually grasp it once the bigger picture is painted that atoms don't stay neutral in the process of bonding.
I like to end the discussion by asking them, “What kind of elements join to make the different types of compounds”? They are not sure because they are just learning the periodic table, but this question gets them in the right mind set for the next activity.
During the brief discussion at the beginning of class I handout the Bonding Inquiry Activity. I start this activity by explaining that there are several chemical formulas at the top of the page and give them a brief tutorial of how to read chemical equations.
Up to this point we have not discussed how to read chemical formulas, but students should come into chemistry with a basic understanding based on previous science classes and MS-PS1-1.
Most students catch on quickly and realize that a capital letter followed by a lower case is one element symbol and a capital letter followed by another capital letter is two separate elements. The part that most students have questions about is the subscript.
To alleviate any confusion I model the first formula, CCl4, on the board and explain that there is one carbon (C) and 4 chlorine (Cl) which is illustrated by the subscript 4. This is typically sufficient for comprehension, but if any students need further clarification I help them individually during the activity.
After modeling how to read a chemical formula I instruct them to place the first element on the periodic table, from part 1, using black pen (or colored pencil) and the second element symbol on the periodic table using another color, then answer questions 1-4. I give them about 5-7 minutes to complete this and then go over the questions. I repeat this procedure with part two.
The main objective of part 1 and 2 of this activity is to establish understanding that one type of bond is between a metal and a nonmetal, and another type of bond is between nonmetal and nonmetal.
After completing part 1 and 2(student work and Key) they are then introduced to the name of the bonds, ionic and covalent, by answering questions 9-11. This should only take about 5 minutes followed by a brief conversation that checks for understanding.
Now that they realize the basic types of bond, I introduce them to Lewis dot diagrams and the octet rule. Lewis dot diagrams (LDD) are easy for most students and takes only a brief explanation. I will model how to make them by demonstrating Na, N, Cl and Xe as in this video.
After the brief description, most students understand and are ready to complete the dot diagrams that are on p.5 of the Bonding Inquiry Activity (student work). In addition to drawing the dot diagrams, I ask students to write next to the LDD whether the element will gain or lose electrons to create an octet. A brief explanation that an octet is 8, and metals will lose electrons and nonmetals will gain electrons to achieve 8 valence electrons gives students ample guidance to complete this.
As a final step I want them to write whether the element will become positive or negative after gaining or losing electrons. I explain to students that metals will lose electrons and become positive cation and nonmetals will become negative anions. I write this on the board so they can see it while doing the activity.
I then teach them that an easy way to remember anion and cation is that anion is "a-negative-ion and a cation is "a-+-ion". I then explain that the n in anion is the first letter in "negative" and the "t" in cation looks like a + sign. This is a quick and easy explanation that works almost every time.
As they are working on this part of the activity I will group the struggling students together and help them with the activity. By doing this I can save energy and the students will learn from one another's questions.
At the very end of the class I do a white board review. I always have white boards and markers out at their lab tables so I can quickly assess them. They are used to this, so the transition time is less than a minute.
After the review I instruct them to complete the assignment for homework (if not completed) because it will be checked in and reviewed first thing tomorrow.
These 4 questions summarize the lesson and takes less than five minutes: