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Valence bonds?

  • Thread starter LakeMountD
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Here is what the problem states.

The most common elements found in organic compounds usualy bond covalently in the same fashion. This consistent bonding pattern or valence may be designated by an integer. For each of the following elements indicate its customary valence. Valence=number of bonds that are usuall formed.

Choices- 0,1,2,3,4,5,6

A. H Anion
B. C Cation
C. Br
D. H+
E. N Cation

I need to assign the number of bonds that A-E has. I am kinda lost since I haven't had chem in a while. Thanks for the help guys.
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Answers and Replies

Gokul43201
Staff Emeritus
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I'm tempted to tell you to go back to your teacher and ask for an intelligent question instead. Typically, the valence is defined as the number of valence (or outer shell) electrons in an atom of the element. Valency is not defined strictly for an ion, though the definition above could be extended to include ions. Defining valence as the number of (covalent) bonds formed, and then asking for the valence of (poorly specified) ions makes no sense to me.

But I suggest you wait for someone (like GCT, perhaps) to come along, who might have better advice for you.
 
lightgrav
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The chem folks define valence like Gokul described.
Even the physiology textbooks define it that way!
What subject is this question related to?

What's true is that the number of valence electrons
+ the number of covalent bonds formed ,
should = the shell-closing number for that shell.
The number of ionic bonds formed should =
the |number of elementary charges| of the ion.

H aNion is the Negatively charged ion H-
with (one regular + one extra) electrons, it has
two valence electrons, and will form 1 ionic bond.
Hydrogen retains *some* of its "ionic" character
after bonding - hence "ionic" bond is OK.
With closed valence shell, 0 covalent bonds form.

C atom has (2)+4 valence electrons. (closed s-shell)
C ca+ion is C+ ion, so has only 3 valence electrons.
You might expect to be able to make C+ ions by
immersing Carbon in F or Chlorine, forming C+Cl- , but
what actually happens is that it makes CCl_4,
with 4 bonds just as if it were an atom (not ion).
Reasonable humans interpret this behavior as if
all 4 bonds are covalent (electron sharing) bonds.

Bromine has built (2)+(10) + 5 valence electrons
onto the inert Argon core. It seldom forms 5 bonds.
The valence shell becomes full (essentially like Kr)
by sharing 1 electron, as 1 covalent bond.

H+ doesn't have any electrons, it's a proton.
They exist in water for a picosecond before
bonding to one H20 to form hydronium, H3O+

N atom has (2) + 3 valence electrons on He core.
The N+ ion would only have 2 valence electrons.
If N+ made one ionic bond (say, with F-, forming NF)
it would need 4 covalent bonds for a closed shell.
That would suggest NF_5 , which is not reality.
Instead, N in F makes NF_3 , as 3 covalent bonds.
 
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