Introduction
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Oxidation Number is the positive or negative number associated with the ability of an atom to lose or gain electrons. Atoms lose or give up electrons in order to become stable. If atoms lose or give up electrons they acquire positive oxidation numbers. If the atoms accept electrons, they acquire negative oxidation numbers. Metals which are located at the left side of the periodic table lose electrons and thus have positive oxidation state.
Valence Electrons are electrons in the outermost shell of an atom. Generally atoms with the same electrons are grouped together. Valence electrons are important in determining the oxidation number of an atom.
Task
At the end of the lesson, the student should be able to:
1. State the importance of valence electron in determining the oxidation number.
2. Determine the oxidation number of an atom.
Process
Strategies: Lecture, Boardwork
Values Integration: Decision-making
Procedure:
Routine
a. Classroom PreparationRoutine
b. Prayer
c. Attendance
Question: How an element are arranged in Periodic Table?
Answer: They are arranged by group. They grouped according to the number of their valence electrons.
Example: Co will give up 2 electron in order to become stable, so it's oxidation number is +2.
The table below summarizes the oxidation numbers of an atom based on the number of their valence electrons.
| Valence Electrons | Oxidation Number |
| 1 | +1 |
| 2 | +2 |
| 3 | +3 |
| 4 | +4 and -4 |
| 5 | -3 |
| 6 | -2 |
| 7 | -1 |
| 8 | 0 |
Group IVA elements such as C and Si may acquire an oxidation number of either +4 or -4, depending on the type of chemical bond formed.
Question: As you observe class on the table, an atom with 8 valence e- has an oxidation number of zero. Why?
Answer: Elements of group 8 have an oxidation number of zero. They are already stable and they do not lose or gain electrons.
Give the valence electron of the following:
1. Li 2. Ba 3. Ge 1. Li - 1 2. Ba - 2 3. Ge - 4
4. Br 5. B 4. Br - 7 5. B - 3
Question: What is valence electrons?
Answer: Valence electrons are electrons in outermost shell of an atom. Generally atoms with the same electrons are grouped together. Valence electrons are important in determining the oxidation number of an atom.
Questions: What is an oxidation number of an atom?.
Answer: Oxidation number is the positive or negative number associated with the ability of an atom to lose or gain electrons.
All elements/atoms that belongs to group 1A have a valence electron of 1. Therefore in order to become stable they will lose or give up 1 electron, so there oxidation number is +1.
Example: Give the possible oxidation number of Ca.
Answer: Ca has 2 valence electrons; therefore the oxidation number of Ca is +2.
Evaluation
Fill-up the table below:
| Element | Valence Electron | Oxidation Number |
| Ba | ||
| Si | ||
| Al | ||
| P | ||
| F |
Conclusion
Valence electrons are important in determining the oxidation number. An atom that gives up electron has positive oxidation number, and the atom that accepts electron acquire negative oxidation numbers. Elements of group 8 have an oxidation number of zero. They are already stable.
Credits
The maker of this webquest is Ms. RHIA ANGELIC S. MARAVILLA. The maker wants to express her sincerest thanks and gratitude to all persons who extend their understanding, faith and inspiration in the completion of this webquest. She would like to thanks Professor Gerard M. Protacio for his encouraging words that helped her a lot to pursue this webquest, for without his encouraging support, this endeavor will not come to success or fruition. To her classmates for sharing their knowledge and ideas. Last but not the least, she would like to thanks our Almighty God, for giving her the time and good health, and above all the guidance and knowledge.
References:
http://ts2.mm.bing.net/th?id=HN.608026124906793761&pid=15.1
Chemistry for the New Millenium, Soriano Emil F. et al, pages 136-138
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