In this lesson, students will learn about how and why atoms combine to form ionic and covalent bonds. Compound: A substance formed by the chemical combination of elements in defined proportions.
Electronegativity: A measure of the attraction of an atom for the electrons in a covalent bond. Ionic Bond: Bond formed between oppositely charged ions because of electrostatic forces of attraction. Lewis Dot Structure: A diagram to represent the valence electrons of an atom, written as the element symbol surrounded by dots that represent the valence electrons. Molecule: A unit of matter formed by the chemical bonding of two or more atoms by covalent bonds. Octet Rule (Noble Gas Rule): Rule that states that atoms tend to combine in such a way that they each have eight electrons in the highest main energy level, giving them the same electronic configuration as a noble gas.
The possible inclusion of commercial websites below is not an implied endorsement of their products, which are not free, and are not required for this lesson plan. Collect and assess the Valence Electrons and Lewis Dot Structures, Octet Rule Chart, and Ionic versus Covalent Bonding worksheets. Assess students’ abilities to create models of compounds that have ionic and covalent bonding.
This lesson on ionic and covalent bonding includes many examples for students, as well as guided and independent practice.
The lesson begins by having students diagram the structure of an atom, based on what they already know. Students revisit the concepts through practice problems on worksheets and in a graphic organizer that compares ionic and covalent bonding. Students express their understanding of the concepts by drawing diagrams and building models. This lesson can be tailored by providing additional examples and guiding students through the solutions for the practice problems. The lesson begins with an explanation of how to use the periodic table to determine whether elements will join to form ionic or covalent bonds.
To review background knowledge, this activity asks students to build models of ionic and covalent bonds between atoms. To introduce the lesson, have students answer the following prompt in their science notebooks. Explain that when atoms combine, only the electrons in the outermost energy level are involved. Tell students that the number of valence electrons is equal to the group number for representative elements. Tell students that we can use a diagram called a Lewis dot structure to draw an atom with its valence electrons.
Hand out Valence Electrons and Lewis Dot Structures (S-C-6-1_Valence Electrons and Lewis Dot Structures and KEY.doc).
Tell students that Lewis dot structures can be used to show how the arrangement of electrons changes when atoms combine to form compounds. Explain the octet rule, that states that atoms tend to combine in such a way that they each have eight electrons in the highest main energy level, giving them the same electronic configuration as a noble gas.

Guide students step-by-step in completing the Octet Rule Chart (S-C-6-1_Octet Rule Chart and KEY.doc).
Define ions as atoms that have acquired an electrical charge by either gaining or losing electrons. Next, explain the concept of electronegativity, which is a number that describes the ability of an atom to attract electrons when it forms a bond with another atom.
Tell students we can determine the type of bond based on the difference in electronegativity between atoms. Explain that when Na combines with Cl, the Na becomes a cation (positive ion), and the Cl becomes an anion (negative ion). Have students practice by drawing Lewis dot structures to show how a bond forms between Li and F. Hand out the worksheet Ionic versus Covalent Bonding (S-C-6-1_Ionic versus Covalent Bonding and KEY.doc).
Explain to students that they will demonstrate their understanding of ionic and covalent bonds by creating models of them. Have each pair of students draw a slip of paper from the bag containing simple ionic bonds, and draw a slip from the bag containing simple covalent bonds. To close the lesson, have each student diagram three-dimensional models of ionic and covalent bonds, labeling each atom and the type of molecule that is shown.
Students who might need an opportunity for additional learning can color-code the electrons from different elements in a compound. During the lab, students who may be going beyond the standards can create models of more complex molecules, such as O3 (ozone), Al2O3 (aluminum oxide), or H2SO4 (sulfuric acid).
Assess students’ understanding as you guide them through the examples and go over those as well as the Ionic Bonding and Covalent Bonding worksheets with the class. This activity gets them thinking about the position of electrons in relation to the nucleus. Then the octet rule is introduced so that students see how atoms fill their energy levels when they bond together. On the board, draw the Lewis dot structures of a carbon atom and a magnesium atom, as shown below. Tell them that we can use the periodic table to predict which elements are more likely to bond with one another. For now, just tell students that atoms in covalent bonds share electrons and atoms in ionic bonds transfer electrons. Give students copies of Electronegativity Trends in the Periodic Table (S-C-6-1_Electronegativity Trends.doc). If needed, review how to use the octet rule to find the ionic charge for atoms of various elements from Day 1. Explain that atoms will follow the octet rule when they form bonds, so that their valence shells are full.
Have them complete the worksheet individually or in pairs, and then go over the answers with the class.
Explain the electron shell diagram and the Lewis dot structure as you draw them on the board and have students copy them into their notes. Divide students into pairs, and give each pair a bag containing the gumdrops and bamboo skewer pieces.

Students should use the materials in their bags to create models of the ionic and covalent bonds they have selected.
For example, in H2O, the hydrogen electrons may be black and the oxygen electrons may be red. Show students how to use the group number of an element to determine the number of valence electrons.
Show students a picture of covalent and ionic bonds (S-C-6-1_Covalent and Ionic Bonds.doc). When sodium and chlorine bond together, sodium becomes an ion (Na+), because it has lost one electron. Provide more examples of ionic bonding and ask questions about them to assess students’ understanding of the concept. Use the sample bag of materials to explain the purpose of the different materials by creating a model of sodium chloride (NaCl) as an example. Tell students that depending on the bonds they are creating, they may not use all of the materials. It may be helpful to have students manipulate coins or other objects to represent the sharing or transfer of electrons in ionic and covalent bonding. Then they practice the concepts on worksheets and by constructing models of compounds with ionic and covalent bonds.
For example, ask them how many electrons a carbon atom has (6), and then tell them that there are two electrons in the first energy level and four valence electrons. They are very stable because the s- and p- sublevels in the highest main energy level are filled.
Point out to students that ionic bonding occurs between metals and nonmetals, and covalent bonding occurs between two nonmetals. If they have not already done so, guide students in labeling or color-coding the metals and nonmetals on their periodic tables. When pairs finish a model, have them raise their hands to notify you that they are ready for you to check the model.
Provide students with additional examples of ionic and covalent bonding, and allow extra time for reviewing the practice problems step-by-step.
Check for understanding by asking students the number of valence electrons for several other elements, such as calcium, boron, and silicon.
Have them recall the Lewis dot structure for sodium (from the worksheet), and ask how many valence electrons it has.
Once you approve a model, the pair should tape the slip of paper with the type of bond to one of the skewers. Students should note that there are two colors of gumdrops, and each atom to be created should use one color; for example, if creating sodium chloride, the electrons in the sodium atom should be one color and the electrons in the chlorine atom should be the other color.
If time permits, these slips can be removed and students can use their knowledge of the elements to determine what molecules and types of bonds are being represented. The different lengths of bamboo skewers will help students create the different energy levels of electrons.

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