## Definitions?
Ionic= Can't see it, contributes to conductivity. Can measure it with a
meter.
Particulate= Can see it as TE, doesn't conduct. Can't measure it with a
meter.
Colloidal= Can see it, Can't measure it....didn't settle out.
Ode
Dan Nave wrote:
Read the following excerpt. I am certainly no chemist, but the
explanation of the difference between the Ionic and Metallic bond may
be the key to the distinction you are trying to make.
(The colloids which we are interested in would consist of groups of
metallically bonded silver atoms, I would think...)
Dan
http://www.answers.com/topic/chemical-bond
CHEMICAL BOND, mechanism whereby atoms combine to form molecules.
There is a chemical bond between two atoms or groups of atoms when the
forces acting between them are strong enough to lead to the formation
of an aggregate with sufficient stability to be regarded as an
independent species. The number of bonds an atom forms corresponds to
its valence. The amount of energy required to break a bond and produce
neutral atoms is called the bond energy. All bonds arise from the
attraction of unlike charges according to Coulomb's law; however,
depending on the atoms involved, this force manifests itself in quite
different ways. The principal types of chemical bond are the ionic,
covalent, metallic, and hydrogen bonds. The ionic and covalent bonds
are idealized cases, however; most bonds are of an intermediate type.
The Ionic Bond
The ionic bond results from the attraction of oppositely charged ions.
The atoms of metallic elements, e.g., those of sodium, lose their
outer electrons easily, while the atoms of nonmetals, e.g., those of
chlorine, tend to gain electrons. The highly stable ions that result
retain their individual structures as they approach one another to
form a stable molecule or crystal. In an ionic crystal like sodium
chloride, no discrete diatomic molecules exist; rather, the crystal is
composed of independent Na+ and Cl− ions, each of which is attracted
to neighboring ions of the opposite charge. Thus the entire crystal is
a single giant molecule.
The Covalent Bond
A single covalent bond is created when two atoms share a pair of
electrons. There is no net charge on either atom; the attractive force
is produced by interaction of the electron pair with the nuclei of
both atoms. If the atoms share more than two electrons, double and
triple bonds are formed, because each shared pair produces its own
bond. By sharing their electrons, both atoms are able to achieve a
highly stable electron configuration corresponding to that of an inert
gas. For example, in methane (CH4), carbon shares an electron pair
with each hydrogen atom; the total number of electrons shared by
carbon is eight, which corresponds to the number of electrons in the
outer shell of neon; each hydrogen shares two electrons, which
corresponds to the electron configuration of helium.
In most covalent bonds, each atom contributes one electron to the
shared pair. In certain cases, however, both electrons come from the
same atom. As a result, the bond has a partly ionic character and is
called a coordinate link. Actually, the only purely covalent bond is
that between two identical atoms.
Covalent bonds are of particular importance in organic chemistry
because of the ability of the carbon atom to form four covalent bonds.
These bonds are oriented in definite directions in space, giving rise
to the complex geometry of organic molecules. If all four bonds are
single, as in methane, the shape of the molecule is that of a
tetrahedron. The importance of shared electron pairs was first
realized by the American chemist G. N. Lewis (1916), who pointed out
that very few stable molecules exist in which the total number of
electrons is odd. His octet rule allows chemists to predict the most
probable bond structure and charge distribution for molecules and
ions. With the advent of quantum mechanics, it was realized that the
electrons in a shared pair must have opposite spin, as required by the
Pauli exclusion principle. The molecular orbital theory was developed
to predict the exact distribution of the electron density in various
molecular structures. The American chemist Linus Pauling introduced
the concept of resonance to explain how stability is achieved when
more than one reasonable molecular structure is possible: the actual
molecule is a coherent mixture of the two structures.
Metallic and Hydrogen Bonds
Unlike the ionic and covalent bonds, which are found in a great
variety of molecules, the metallic and hydrogen bonds are highly
specialized. The metallic bond is responsible for the crystalline
structure of pure metals. This bond cannot be ionic because all the
atoms are identical, nor can it be covalent, in the ordinary sense,
because there are too few valence electrons to be shared in pairs
among neighboring atoms. Instead, the valence electrons are shared
collectively by all the atoms in the crystal. The electrons behave
like a free gas moving within the lattice of fixed, positive ionic
cores. The extreme mobility of the electrons in a metal explains its
high thermal and electrical conductivity.
Hydrogen bonding is a strong electrostatic attraction between two
independent polar molecules, i.e., molecules in which the charges are
unevenly distributed, usually containing nitrogen, oxygen, or
fluorine. These elements have strong electron-attracting power, and
the hydrogen atom serves as a bridge between them. The hydrogen bond,
which plays an important role in molecular biology, is much weaker
than the ionic or covalent bonds. It is responsible for the structure
of ice.
Bibliography
See L. Pauling, The Nature of the Chemical Bond (3d ed. 1960); A. L.
Companion, Chemical Bonding (2d ed. 1979).
Subject: CS>Ionic vs Particulate
From: Marshall Dudley <[email protected]
Date: Fri, 23 Dec 2005 12:15:46 -0500
To: [email protected]
My decision to ask the definition of ionic in the sci.chem newsgroup
does not seem to have worked out as well as I had hoped. Initially
there was confirmation that the silver oxide/hydroxide is ionic and
that the silver crystals were particulate with a charge but not
ionic. Then other scientists/chemists chimed in and said that the
particulate could be called ionic, and even went as far as to say that
if you rub a diamond on silk and charge it up, it could be called an
ion! Also one indicated that radicals are ions, but not molecules, but
another one said that radicals are molecules, that a molecule does not
have to be neutral.
How the heck can we agree on terms if the professional chemists and
scientists cannot agree on the terms? After one of them suggested that
we use the term "molecular ion" to describe the dissociated salts of
anything, including silver another researcher chimed in last night and
said that "molecular ion" is already used "in mass spectrometry for
the molecule that has acquired a +1 charge and has not been
fragmented. Also called parent peak."
So I am still somewhat at a loss here as to what terminology to use to
definitively separate a molecular silver ion from a suspended silver
crystal. I still like the "molecular ion", but maybe another good
term would be a "disassociated ion". There is obviously a difference
between the disassociated ion of what we call ionic silver, and the
particulate portion of EIS.This is easily proven with both a laser as
well as by adding salt and seeing that the former falls out and the
latter does not. The difference is like the difference in salt water,
and a diamond that has been charged up. The disassociated ion is very
reactive, and the diamond is very stable.
Any other ideas?
Marshall
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