Slide 1

Slide 2 Atoms and the Periodic Table Chapter Six: The Atom Chapter Seven: Elements and the Periodic Table Chapter Eight: Molecules and Compounds Slide 3 8.1 Compounds and Chemical Bonds 8.2 Electrons and Chemical Bonds Slide 4 Investigation 8B What are some molecules and compounds and what atoms are in them? Molecules and Compounds Slide 5 8.2 Electrons and chemical bonds Chemical bonds are formed only between the electrons in the highest unfilled energy level. These electrons are called valence electrons. Slide 6 Slide 7 8.2 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? Slide 8 8.2 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? Slide 9 Slide 10 8.2 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? Slide 11 Slide 12 8.2 Predicting a chemical formula When elements combine in molecules and ionic compounds, the total electric charge is always zero. Slide 13 Slide 14 Slide 15 8.2 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. Slide 16 Slide 17 8.2 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 Slide 18 Activity In this activity, you will build some simple molecules out of gumdrops and toothpicks. How many toothpicks and gumdrops (and what colors?) would you need to build this molecule? Molecular Gumdrop Models