1. SYNTHESIS AND DECOMPOSITION REACTIONS ELEMENTS AND THEIR OXIDES
Chapter 4.1 & 5.3
SYNTHESIS AND DECOMPOSITION REACTIONS
ELEMENTS AND THEIR OXIDES

2. Another good one:
REVIEW: homework and major concepts from previous lesson (chem reaction, law of conservation of mass)

3. Predicting Chemical Reactions
Using the periodic table, we can figure out the properties of the elements Ex. H, N, O, F, Cl, Br, I elements are all diatomic
Since the properties of the elements are predictable, the chemical reactions they undergo are also predictable Ex. Na and K are both alkali metals that react with Cl to form very stable compounds
Because we can predict chemical reactions most of the time, chemists classify reactions. Today we will cover two types of chemical reactions.

4. Synthesis Reactions
Two reactants combine to make a larger, more complex product
What does it mean to synthesize something?
Synthesis reaction between sodium and chlorine:

5. Synthesis of Ionic Compounds
Metal + Non-Metal  Ionic Compound
Ex. 2 K (s) Cl2 (g)  2 KCl (s)
REMEMBER: Always apply the criss cross rule when making ionic compounds!
Do the KCl equation on the board to show crossing of charges

6. Synthesis of Molecular Compounds
Non-metal + Non-metal  Molecular compound
Can involve:
HYDROGEN: Easy to predict because H usually forms molecular compounds and follows general pattern of synthesis
Ex. H2 (g) + F2 (g)  HF (g)
NO HYDROGEN: difficult to predict because the reaction depends on reaction conditions Ex. C and O can make CO or CO2 depending on the amount of oxygen available to react

7. Oxides– A Special Type of Synthesis
Oxide: a compound made up of any element and oxygen
Basic oxides Mg + O2  MgO MgO + H2O  Mg(OH)2
Acidic oxides CO2 (g) + H2O (l)  H2CO3 (aq) SO3 (g) + H2O (l)  H2SO4 (aq) NO2 (g) + H2O (l)  HNO3 (aq) + HNO2 (aq)

8. Recall:
pH < 7 = acidic solution, pH= 7 neutral solution, pH > 7= basic solution
Acids produce H+ ions in solution
Bases produce OH- ions in solution

9. Decomposition Reactions
A compound breaks down to form two or more simpler products
Generally need energy (heat, catalyst, electricity) to get started
What do you notice about this reaction? Opposite of synthesis

10. Decomposition of Ionic Compounds
Ionic compound  Element + Element
Ex. 2 KCl (l) 2 K (s) + Cl2 (g) This reaction involves passing electricity through KCl to break it down into its elements K and Cl

11. Decomposition Involving Compounds
Compounds with polyatomic ions or molecular compounds are difficult to predict
Use chemical tests to detect what the products are (often testing for presence of gas) Ex. 2 KClO3  2 KCl + 3 O2
Ex. CaCO3  CaO + CO2
Note: Both reactions require heat
A chlorate will break down into a metal chloride and oxygen gas
A carbonate will break down into a metal oxide and carbon dioxide

12. Examples Identify the reaction type: 2 HCl  H2 + Cl2
Cl2O (g) + H2O (l)  2 HClO (aq)
2 AlCl3 (s)  2 Al (s) Cl2 (g)
KO (g) + H2O (l)  2 KOH (aq)
Synthesis
Synthesis – acidic oxide (nonmetal and oxygen) because of acid product
Decomposition
Synthesis – basic oxide (metal and oxygen) because of basic product

13. Some Helpful Links
Synthesis and decomposition reactions explained:
Basic and acidic oxides:

14. Homework
pg. 161 # 1, 2, 4 pg. 204 #3, 4, 9