Re: electron energies in covalent bonds

On Feb 6, 12:04 pm, s...@xxxxxxxxxxxx wrote:
On 5 fév, 21:30, "The_Man" <me_so_hornee...@xxxxxxxxx> wrote:





On Feb 5, 5:24 pm, s...@xxxxxxxxxxxx wrote:

On 4 fév, 15:43, "The_Man" <me_so_hornee...@xxxxxxxxx> wrote:

On Feb 2, 12:38 pm, s...@xxxxxxxxxxxx wrote:

On 2 fév, 11:49, jthesav...@xxxxxxxxx wrote:

Hi all,
Consider ammonia, NH3. Each hydrogen atom shares an electron
with the nitrogen. However, the hydrogen sees the electron as being
in its 1s shell, but the nitrogen sees it as being in its 2p shell.
Don't those two shells have different energy levels? And doesn't that
mean that the electron has two different amounts of energy at the same
time? How can this be?

Thanks,
John

Each covalent bound involves 2 electrons, one from each atom and
in antiparallel spin relation.

Not if it is a coordinate covalent (aka "dative") bond, in which case
BOTH electrons come from the same atom.

Possible but not the usual case.

"Not the usual case"??? Whenever a Bronsted-Lowry acid reacts with a
Bronsted-Lowry base, we have formation of a coordinate covalent bond
between the H+ (which of course has no electrons) and the atom with
the lone pair. Are you suggesting that Bronstead-Lowry salts are
"unusual".

They are not. You seem to forget or not be aware that protons do not
float about freely in nature.

The proton (or its functional equivalent, the hydronium ion H3O+) is
present in a concentration of 10^-7 M in pure water, and 1 M in 1,0 M
strong acid.


Before the reaction, what you have is a hydrogen atom (one proton
accompanied by 1 electron) contributed by other molecules or
typically hydrogen molecules (2 protons covalently bound by
2 electrons) which upon separating resolve into two single
hydrogen atoms recuperating each its electron to then contribute
it to a new covalent bound with other atoms.

Now you are talking unusual. It is uncommon for H2 to dissociate into
2 hydrogen atoms. For this to happen, you need a catalyst such as Ni,
Pt, or Pd. This is commonly used to reduce alkenes and alkynes, but is
far less common than hydrogen as H+.

Hydrogen can also bring TWO electrons (as hydride), as generated from
NaBH4 (sodium borohydride) or LiAlH4 (lithium aluminum hydride).


In any reaction where hydrogen is involved, it contributes its single
electron to the covalent bound, while the protons remains hanging
out from the bounded atom.

No, it only does those where hydrogen ATOMS are generated, which
requires a special catalyst, and is far less common than reactions as H
+.


Plus add to this all the cases where we have a LEWIS acid like BF3
or AlCl3, which is electron deficient, and it reacts with a Lewis base
like ammonia. Yes, these reactions are VERY rare, unless you are a
chemist...

Well, "electron deficient" in the chemical sense does not mean that

It certainly CAN mean that - metal ions are typically Lewis acids, for
just that very reason.

the atom is ionized and that it electrostatically is missing even one
electron. It only means that some of its electrons are not paired, and
cannot be in the single atom unles the atom become negatively
ionized.

There are many electron deficient species which are uncharged (BF3,
BCl3, AlCl3, HF, etc.), but that is hardly required.


They form regular covalent bound (as many as you have naturally
unpaired electron in the single atom) with as many other atoms
if circumstances allow, each contributing one of its own unpaired
electron to the bound.

I can appreciate that you have never learned about coordinate covalent
bonds, but that doesn;t mean that they don't exist, and that they
aren't important.


And take metal ions, which are frequently electron deficient, and
form coordinate covalent bonds with Lewis bases we call ligands. 3/4
of all enzymes have metals as cofactors or in prosthetic groups, so I
guess coordinate covalent bonds are "not usual", except if you are a
chemist or biochemist.

Physically speaking, they are normal covalent bounds with 1 naturally
unpaired electron from one atom being associated with 1 naturally
unpaired electron from some other atom.

No! In the reaction of BF3 with NH3, a bond forms between boron and
nitrogen, where are the "naturally unpaired" electrons in the bond?





Two different amounts of energy are
inded contributed from each nucleus. They simply add up.

Simply worng.

You are wrong on this one.

How? One MIGHT be able to extract some meaning from "different amounts
of energy are contributed from each nucleus" if you wanted to wave
your hands over the whole thing.

What is "different"? The potential energy contribution from each
nuclear charge (in the one elctron approximation) depends on both the
charge and the DISTANCE SQUARED, for EACH nuclei. How does this jive
with "they simply add up."?

Yes. On the new resulting orbital, the local energy of both electrons
(besides
their rest energy) can only be the sum of the energies contributed by
the force acting as a function of the inverse square of the distances
involved between both electrons and both nuclei.

You are mistaken here. I was mistaken when I wrote "distance squared"
- of course, it is distance squared for the FORCE, not the potential
energy (my bad on that one). The potential energy is Z/r, where Z is
the nuclear charge, and r is the distance from the nucleus to the
electron.


The covalent bounding energy is separate.

Where do you think covalent bonding comes from? You have the
attraction of each nuclei for each electron, the nuclear-nuclear
repulsion, and the electron-electron repulsion (which consists of both
correlation and exchange).


André Michaud- Hide quoted text -

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