Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: mememehere on November 28, 2009, 10:10:28 PM
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What's the difference between oxidation number/states and valency number?
What's vlance electrons too?
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anybody know? ::)
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Valence electrons are the electrons that participate in forming chemical bonds. For example, lets look at the element carbon. Carbon has a total of 6 electrons (you can tell this by looking at the periodic table). However, 2 of those electrons are in the core of the atom ( in the 1s orbital). The remaining 4 electrons are in the outer 2s and 2p orbitals. Since these 4 electrons are in the outer shell, they can participate in bonding. Therefore since there's 4 electrons that carbon can share, we say that carbon has a valency (or as you call it a valency number) of 4.
Oxidation state is a number used to designate how oxidized an atom is in a compound or molecule. It is the hypothetical charge an atom would have if all of its bonds were completely ionic (rather than covalent). Really oxidation state is a book-keeping formalism that allows us to track what is being oxidized or reduced in a chemical reaction by comparing the oxidation states of the reactants to those of the products.
Hope that helps.
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Please give me any example of oxidation state:)
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For example, water: H2O
oxygen atom is more electronegative than hydrogen atoms, so we consider that it keeps all the shared electrons for itself:
H-O-H ---> H+ O2- H+
The oxidation number of oxygen is -2.
The oxidation number of hydrogen is +1.
Remark, the oxygen atom has 8 valence electrons: 2 lone pairs (with 2 electrons each) and 2 bonds O-H (again, with 2 electrons each)
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and an example for valency electron.
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What about these?
Cs, Fr: Valence 3, should be 1..
F: 1, Cl: 5, should be 7..
Oxygen: 2
Nitrogen: 3
Some of this doesn't make sense..
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^^ That was a question, not an answer, meme :)
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and an example for valency electron.
For example: oxygen
The electronic configuration of oxygen is 1s22s22p6. There are two core electrons that are in the atomic orbital 1s. There are six valence electrons that are in the atomic orbitals 2s and 2p.
Electrons in atoms are distributed in layers. The more electrons an atom has, the more layers there are.
As you pile up electron layers, the electrons that are closer to the atom nucleus are buried under the successive layers --> they can't react anymore to form bonds. They are core electrons.
Valence electrons are the one on top of the pile, which are accessible to form bonds and molecules...
What about these?
Cs, Fr: Valence 3, should be 1..
F: 1, Cl: 5, should be 7..
Oxygen: 2
Nitrogen: 3
Some of this doesn't make sense..
Where did you get those numbers from? Some of them are wrong. And it looks like they refer to the number of unpaired electrons, and not to the number of valence electrons.
Cs and Fr have only 1 valence electron each. They can easily give it away to form Cs+ and Fr+, which have electronic configurations similar to related noble gases. Cs+ and Fr+ are more inert.
F and Cl have 7 valence electrons. They are just missing 1 electrons to fulfil their orbitals and form F- and Cl-.
Oxygen has 6 valence electrons. It has 2 unpaired electrons which are available to form 2 bonds.
Nitrogen has 5 valence electrons. It has 3 unpaired electrons ready to form 3 bonds.
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they're from ptable.com
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OK, I had a look at this website. It looks nice and clear. :)
By clicking on "properties" and selecting the "valence" option, I found the numbers you mentioned. There is as well the explanation written just above the lanthanide group:
"Valences for the majority of elements are based on the highest known fluoride."
That explains everything. We are not talking about the same thing. :P
So, concerning the numbers you mentioned:
What about these?
Cs, Fr: Valence 3, should be 1..
F: 1, Cl: 5, should be 7..
Oxygen: 2
Nitrogen: 3
Some of this doesn't make sense..
Because of the compounds:
CsF3
FrF3
F-F
ClF5
OF2
NF3