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Explore atoms, molecules, and compounds in this comprehensive guide. Learn about valence electrons, Lewis dot diagrams, oxidation numbers, and more. Discover the differences between ionic and covalent bonds. Engage in a hands-on activity creating molecular models using gumdrops and toothpicks.
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Atoms and the Periodic Table • Chapter Six: The Atom • Chapter Seven: Elements and the Periodic Table • Chapter Eight: Molecules and Compounds
Chapter Eight: Molecules and Compounds • 8.1 Compounds and Chemical Bonds • 8.2 Electrons and Chemical Bonds
Investigation 8B Molecules and Compounds • What are some molecules and compounds and what atoms are in them?
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.
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?
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?
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 numberof 1+. What is the most common oxidation number for nitrogen?
8.2 Predicting a chemical formula • When elements combine in molecules and ionic compounds, the total electric charge is always zero.
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.
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
Activity Molecular Gumdrop Models • 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?
