2. Atoms, Elements, and Compounds

3. Chapter Fifteen: Molecules and Compounds 15.1 Compounds and Chemical Bonds 15.2 Electrons and Chemical Bonds

4. Investigation 15B What are some molecules and compounds and what atoms are in them? Molecules and Compounds

5. 15.2 Electrons and chemical bonds Chemical bonds are formed only between the electrons in the highest unfilled energy level. These electrons are called valence electrons.

7. 15.2 Electrons and chemical bonds Going from left to right across a period each new element has one more valence electron than the one before it. How many valence electrons does nitrogen have?

8. 15.2 Lewis dot diagrams A clever way to keep track of valence electrons is to draw Lewis dot diagrams. A dot diagram shows the element symbol surrounded by one to eight dots representing the valence electrons. What is the dot structure for nitrogen?

10. 15.2 Oxidation numbers An oxidation number indicates the charge on the remaining atom (ion) when electrons are lost, gained, or shared in chemical bonds. A sodium atom always ionizes to become Na+ (a charge of +1) when it combines with other atoms to make a compound. Therefore, we say that sodium has an oxidation number of 1 +. What is the most common oxidation number for nitrogen?

12. 15.2 Predicting a chemical formula When elements combine in molecules and ionic compounds, the total electric charge is always zero.

15. 15.2 Ionic and covalent bonds On the periodic table, strong electron donors are the left side (alkali metals). Strong electron acceptors are on the right side (halogens). The further apart two elements are on the periodic table, the more likely they are to form an ionic compound.

17. 15.2 Ionic and covalent bonds Covalent compounds form when elements have roughly equal tendency to accept electrons. Elements that are both nonmetals and therefore close together on the periodic table tend to form covalent compounds.

18. Technology Connection Spiderman’s Favorite Compound The physical properties of gold make it useful in surprising ways. You can find gold in astronaut gear, airplane windshields, and even in some people’s eyelids!

19. Activity Plastic wrap has many household uses. In this activity, you will investigate different polymers used in plastic wrap. Plastics and Evaporation