To the teacher: This CPO Science PowerPoint presentation is designed to guide you through the process of presenting the lesson to your students. The presentation uses a 5-E teaching model: Engage, Explore, Explain, Elaborate, and Evaluate. The PowerPoint Slide notes indicate where you may want to bring in various lesson elements such as quizzes, readings, investigations, animations, and practice materials. Additional science background information is provided in the slide notes where appropriate. You can view these notes by selecting “View,” then “Normal.” You will see the notes pane at the bottom of the PowerPoint workspace. Additionally, the slide notes are available as a separate document, accessible from the lesson home page. The slides that follow are intended for classroom use. About the slide notes: The slide notes for this presentation are available in a separate document that you can print and look at while you use the slides. You can access the slide notes document from your teacher lesson home page. Enjoy the lesson!

What do aspirin, vinegar, and plastic wrap have in common? Aspirin, vinegar, and plastic wrap are all compounds made from different combinations of the same three atoms: carbon, hydrogen, and oxygen. By themselves, these atoms cannot reduce pain, season food, or keep candy clean. But when these atoms chemically combine in certain ways to form compounds, they can be used in may ways. In this module, you will learn how and why atoms combine to form an amazing variety of materials. ENGAGE: Ask students to guess what aspirin, vinegar, and plastic wrap have in common. Once your students have shared their ideas, read the two paragraphs on the slide together. Then, show the class a periodic table (next slide). Point out that only around 100 of the elements occur naturally. From these 100 elements, millions upon millions of compounds and molecules are formed.

The periodic table ENGAGE: Introduce your students to the periodic table, a useful chart of all the known elements. Draw your students’ attention to the fact that only about 100 of the elements occur naturally, yet every known material in the universe is made up of these “building blocks of matter.”

Time to investigate! Complete the lesson investigation: Chemical Bonds EXPLORE: Lead the lesson investigation: Chemical Bonds. At the end of the lesson, assign the student reading.

Identifying elements The number of protons in an element determines that element’s identity. The number of protons is called the element’s atomic number. The atomic number is listed under the element’s symbol on the periodic table. All helium atoms have two protons, and all boron atoms have five. How many protons does a fluorine atom have? EXPLAIN: Remind students that the number under the element symbol on the periodic table tells us how many protons each atom of an element contains. Only one kind of element has a particular number of protons in its nucleus. Ask students to look at a periodic table and name the element that has 8 protons in its nucleus (oxygen). How about 47? (silver)

Electron arrangements A neutral atom has the same number of electrons and protons. The electrons fill the innermost energy level first. It can hold two electrons. The second and third energy levels hold eight electrons each. Look at the electron arrangement for boron. Notice that the electrons in the second energy level spread out, since they repel each other. Can you draw the electron arrangement for fluorine? EXPLAIN: Ask students to draw the electron arrangement for fluorine. The white dots represent unfilled places for electrons and the black dots represent electrons. The first energy level should be filled. The second energy level should have seven out of the eight electron “spots” filled. ?

Valence electrons form chemical bonds The electrons in the highest unfilled energy level are called valence electrons. Valence electrons participate in chemical bonding. Elements heavier than boron form bonds to get eight electrons in their outer shell. Elements with five protons or less need to get two electrons in their outer shell. Hydrogen is a special case, as it can have zero or two electrons in its outer shell. EXPLAIN: Ask students to practice finding the number of electrons in an atom’s valence shell. Have them draw electron diagrams like the one pictured above for a few other elements, such as oxygen (six valence electrons), and beryllium (two valence electrons).

How reactive is an element? In science, reactive means that an element readily forms chemical bonds. The closer an element is to having the same number of valence electrons as a noble gas, the more reactive the element is. Noble gases are not usually reactive because their valence shells are already filled. EXPLAIN: Look closely at the periodic table on the slide. Some students may think that the first column elements shouldn’t be very reactive because they are farthest from the noble gases on the table. But atoms can lose as well as gain electrons. The first column elements have to lose just one electron in order to have a filled valence shell. The numbers at the top of each column address this idea.

Time for Practice! Complete the lesson practice activity: Dot Diagrams ELABORATE: Dot diagrams enable students to demonstrate their understanding of valence electrons and how they determine the reactivity of an element. The lesson animation, which can be accessed from the multimedia lesson home page, introduces students to dot diagrams.

Show what you know! Try the lesson’s interactive quiz, or complete a quiz that your teacher can print out for you. Hint: You might want to review your lesson reading piece one more time before trying the quiz. EVALUATE: Print out the 10-question quiz for students to complete, or have students work individually at computers to complete the interactive quiz they can access from the multimedia lesson home page.