1. Reactions

2. Review 5 Main Types of Reactions: Synthesis Decomposition
Single Replacement
Double Replacement
Combustion

3. Subcategories of Reactions
Precipitation
Acid-Base
Oxidation-Reduction (Redox)

4. Redox Reactions
Chemical reactions in which electrons are ____________ from one chemical species to another.
One species will give away electrons (____________).
Another species must take electrons (____________).
A redox reaction must have reduction AND oxidation; one cannot occur without the other.
Li + Cl

5. Electrically Neutral
Every element on the Periodic Table is electrically _________. This means that they have ________ numbers of protons and electrons. The atomic # determines how many protons/electrons an element has.
Electrons are found outside the nucleus and each electron contributes a 1- charge to the element.
Protons are found in the nucleus and each proton contributes a 1+ charge to the element.
Al = 13 Electrons + 13 Protons
Al = (-13) + (13)
= 0

6. Affect on Charge: Gaining Electrons
Nonmetals tend to gain electrons. Let’s see what affect that has on the overall charge of the atom.
Initially there are 17 electrons
and 17 protons causing the element to be neutral.
Then, 1 more electron is gained to get 8 valence electrons... What overall effect does this have on the charge?

7. Affect on Charge: Losing Electrons
Metals tend to lose electrons. Let’s see what affect that has on the overall charge of the atom.
Initially there are 13 electrons
and 13 protons causing the element to be neutral.
Then, 3 electrons are removed to get 8 valence electrons... What overall effect does this have on the charge?

8. + - Li Li + Cl Cl Redox Reactions, cont.
One species will ___________ electrons (oxidation).
Another species ____________ the electrons (reduction). + - Li Li + Cl Cl

9. Recall:
In order to obtain an octet, metals tend to __________ electrons.
Likewise, non-metals tend to __________ electrons to obtain an octet.
All atoms want to have a stable electron configuration with _____ valence electrons. The group # determines how many valence electrons an element has.

10. 1+ 2+ Metals vs. Non-metals Metals Non-metals
Notice that all the metals are positively charged and all the nonmetals (except H) are negatively charged.
Metals
Non-metals 1+ 2+
The charges of this middle section vary, but they are all positive.

11. Most Likely Oxidation #s
Noble Gases have 8 valence electrons and thus do not want to gain or lose electrons
Metals
Non-metals
Group 4A elements are able to gain 4 OR lose 4 electrons 1+
4+/- 2+ 3+ 3- 2- 1-

12. Rules for assigning oxidation numbers:
All ___________ are zero.
2. Charges of ______ are their oxidation numbers.
3. All ________ without a net charge are zero.
4. Hydrogen is almost always _______ when found in a compound.
5. Oxygen is almost always ________ when found in a compound.
6. If a compound has a net charge, the sum of its atoms’ charges _____________ the net charge.

13. Assigning oxidation numbers: Rule 1
1. Charges of elements are zero.
Zn (s) + HCl(aq)  ZnCl2(aq) + H2(g)
elements

14. Assigning oxidation numbers: Rule 2
Charges of ions are their oxidation numbers. 2+
Zn2+(aq) + HCl(aq)  ZnCl2(aq) + H2(g)
ion

15. Assigning oxidation numbers: Rule 3
All compounds without a net charge are zero.
Zn2+(aq) + Cl2(g)  ZnCl2(aq)
Compound with a net charge of zero
Zn + 2Cl = 0

16. Assigning oxidation numbers: Rule 4
Hydrogen is almost always 1+. 1+
H2O(l)
1+ when paired with _____________. .
1- when paired with ______________. 1-
LiH(aq)

17. Assigning oxidation numbers: Rule 5
Oxygen is almost always 2- when found in a compound. 2-
H2O(l)
2- in almost all ____________.
1- in _________________. 1-
H2O2(aq)
(exception)

18. Zn2+(aq) + Cl2(g)  ZnCl2(aq)
Recall Rule 3:
All compounds without a net charge are zero.
- we can apply this rule along with rules 4 and 5 and our expected oxidation numbers from the periodic table to assign oxidation numbers to elements other than oxygen and hydrogen that are found in compounds
Zn2+(aq) + Cl2(g)  ZnCl2(aq)

19. Calculate Oxidation Numbers for: H2SO4
Net Charge = (# of atoms x Charge) + (# of atoms x Charge)…
0 = (2 x Hydrogen) + (Sulfur) + (4 x Oxygen)
0 = (2H) + (S) + (4O)

20. Assigning oxidation numbers: Rule 6
6. If a compound has a net charge, the sum of its atoms’ charges must equal the net charge.
- we can apply this rule along with rules 4 and 5 and our expected oxidation numbers from the periodic table to assign oxidation numbers to elements other than oxygen and hydrogen that are found in compounds
S(s) + O2(g)  S2O32-(aq)

21. Calculate Oxidation Numbers for: SO42-
Net Charge = (# of atoms x Charge) + (# of atoms x Charge)…
-2 = (Sulfur) + (4 x Oxygen)
-2 = (S) + (4O)

22. Calculate Oxidation Numbers for: ClO3-
Net Charge = (# of atoms x Charge) + (# of atoms x Charge)…

23. Calculate Oxidation Numbers for: NO3-
Net Charge = (# of atoms x Charge) + (# of atoms x Charge)…

24. Why are Oxidation numbers important?L R G
They help us determine which chemical species is oxidized and which chemical species is reduced.
O_________
I_____
L__________
R__________
G__________
Oxidation = Charge ________
Reduction = Charge ________

25. Redox Reactions: Electron Transfer
electrons are ___________ from one species to another (redox).
assign oxidation numbers to identify which loses e– and which gains e– .

26. Redox Reaction: Oxidation Numbers
Oxidation #s help us determine which chemical species is oxidized and which chemical species is reduced.
Zn(s) + O2(g)  ZnO(aq)
Oxidation = Charge Increases
Reduction = Charge Decreases

27. Try This #1: Redox Reactions
Assign oxidation #s and determine which chemical species is oxidized and which chemical species is reduced.
Ag(s) + Cl2(g)  AgCl(aq)
Oxidation = Charge Increases
Reduction = Charge Decreases

28. Try This #2: Redox Reactions
Assign oxidation #s and determine which chemical species is oxidized and which chemical species is reduced.
N2(g) H2(g)  NH3(aq)
Oxidation = Charge Increases
Reduction = Charge Decreases