1. Integrated Science
Unit 7, Chapter 19

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

3. 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.

4. 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

5. *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

6. 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

8. 19.1 The Octet Rule

9. 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

10. 19.1 Valence Electrons

11. 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).

12. 19.1 Covalent Bonds
When electrons are shared between two atoms, a covalent bond is formed.

13. 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.

14. 19.2 Chemical Formulas Key Question:
Why do atoms combine in certain ratios?
*Read text section 19.2 AFTER Investigation 19.2

15. 19.2 Chemical Formulas
All compounds have an electrical charge of zero; that is, they are neutral.

16. 19.2 Oxidation Number
An oxidation number indicates how many electrons are lost, gained, or shared when bonding occurs.

19. Common Polyatomic Ions

20. 19.3 Comparing Molecules Key Question:
What is the meaning of a chemical formula?
*Read text section 19.3 AFTER Investigation 19.3

21. 19.3 Comparing Molecules
One atom of hydrogen is 1/12 the mass of a carbon atom.

22. 19.3 Comparing Molecules

24. 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.