Integrated Science Unit 7, Chapter 19

Unit Seven: Changes in Matter Chapter 19 Molecules and Compounds 19.1 Bonding and Molecules 19.2 Chemical Formulas 19.3 Comparing Molecules

Chapter 19 Learning Goals Relate the chemical behavior of an element, including bonding, to its placement on the periodic table. Identify how elements form chemical bonds and the role of electrons in bonding. Predict the chemical formulas of compounds made up of two different elements. Write chemical formulas for compounds made up of many different types of elements. Calculate the formula mass of a compound and compare different compounds based on their formula masses. Identify the environmental and economic impact of recycling plastics.

Chapter 19 Vocabulary Terms Avogadro number chemical bond chemical formula covalent bond diatomic molecule energy level formula mass ion ionic bond monoatomic ion octet subscript polymer polyatomic ion react valence electron

*Read text section 19.1 AFTER Investigation 19.1 19.1 Bonding and Molecules Key Question: Why do atoms form chemical bonds? *Read text section 19.1 AFTER Investigation 19.1

19.1 Bonding and Molecules The outer electrons are involved in bonding. These are called valence electrons. Most stable atoms have eight valence electrons. (Some have two) When an atom has 8 valence electrons, it is said to have an octet of electrons. 8 1 7 2 6 3 5 4

19.1 The Octet Rule

19.1 Bonding and Molecules A sodium atom is chemically unstable because it has only one valence electron. With the exception of the transition metals, the column of the table tells you how many valence electrons each element has. Columns are called groups. For example, the atoms of the elements in Group 1A have only one valence electron. 1

19.1 Valence Electrons

19.1 Ionic Bonds Ionic bonds are formed when atoms gain or lose electrons. Sodium and chlorine form an ionic bond to make sodium chloride (table salt).

19.1 Covalent Bonds When electrons are shared between two atoms, a covalent bond is formed.

19.1 Ionic or Covalent Bond? Elements can be classified as metals, metalloids, and nonmetals. Generally, bonds between a metal and a nonmetal tend to be ionic in character. Bonds between two nonmetals can be classified as covalent.

19.2 Chemical Formulas Key Question: Why do atoms combine in certain ratios? *Read text section 19.2 AFTER Investigation 19.2

19.2 Chemical Formulas All compounds have an electrical charge of zero; that is, they are neutral.

19.2 Oxidation Number An oxidation number indicates how many electrons are lost, gained, or shared when bonding occurs.

Common Polyatomic Ions

19.3 Comparing Molecules Key Question: What is the meaning of a chemical formula? *Read text section 19.3 AFTER Investigation 19.3

19.3 Comparing Molecules One atom of hydrogen is 1/12 the mass of a carbon atom.

19.3 Comparing Molecules

19.3 Comparing Compounds The Avogadro number is the number of atoms in the atomic mass of an element or the number of molecules in the formula mass of a compound when these masses are expressed in grams. One set of 6.02 x 1023 atoms or molecules is also referred to as a mole of that substance.