To be a molecule, do the bonds between atoms have to be covalent (or can they be ionic)?

Answer 1

Remember that there is a gradient between ionic bonds and covalent bonds: it isn't discrete. Recall the Pauling electronegativity scale... there are some bonds in molecules (especially organometallic structures) that have more of an ionic character than covalent.

Answer 2

Strictly speaking a molecule is composed of atoms that are covalently bond.
However what is a covalent bond?
If you solve the quantum mechanical problem of an NaCl molecule (1 Na atom bond to 1 Cl atom) you would get a result where the valence electrons are almost exclusively orbiting the chlorine atom (in effect Na+Cl- molecule). Does this mean this molecule is ionically bond? I wouldn't say so.
Solve the same problem for an HCl molecule (differs only by replace Na with H) and you would get a similar result, electrons will mostly orbit the chlorine, however you would also orbit the hydrogen to some degree. So is this covalent or ionic?
It gets even worst because if you solve the quantum mechanical system of benzene (for example) you would get states that are covalent (electrons spread all-over the molecule) mixed with ionic states (electrons are fixed around a few atoms but not all).
In the end, who is to say is a molecule is covalently bond or ionic? It all falls down to our interpretation of what we see and how the molecule acts.

Answer 3

A molecule is a discreet arrangement of atoms with a constant structure property relationship. In order to form a stable molecular structure, there must be no localized electrostatic charges present in the system. We call atoms with localized charges ions.

Few bonds are 100% covalent and no bonds are 100% ionic, but as the ionic character of a bond increases, so dose the density of localized charges and the need for those charges to be neutralized by oppositely charged ions.

The take home message: Molecules will have bonds that are higher in covalent character, but do not think of bonding in absolute Covalent vs. Ionic terms.

Answer 4

Just Covalent. Ionic bonds happen when one element takes an electron from another due to higher eletronegativity, this creates an attraction between the two elements causing them to for a 'bond' per se. Covalent bonds are a sharing of electrons between two elements.

Answer 5

Bonding can result in shaing of electrons, transfer of electrons or even intermolecular forces (attraction)... so to be a molecule, the bonds can be ionic or covalent.

Answer 6

Molecules are formed by covalent bonding.

Answer 7

From the Departments of Chemistry and Chemical and Biomolecular Engineering, University of Illinois, Urbana, Illinois 61801

Neural cell adhesion molecule (NCAM) is a cell surface adhesion glycoprotein that plays an important role in the development and stability of nervous tissue. The homophilic binding mechanism of NCAM is still a subject of debate on account of findings that appear to support different mechanisms. This paper describes single molecule force measurements with both full-length NCAM and NCAM mutants that lack different immunoglobulin (Ig) domains. By systematically applying an external, time-dependent force to the bond, we obtained parameters that describe the energy landscape of NCAM-NCAM bonds. Histograms of the rupture forces between the full-length NCAM extracellular domains revealed two binding events, one rupturing at higher forces than the other. These bond rupture data show that the two bonds have the same dissociation rates. Despite the energetic and kinetic similarities, the bond strengths differ significantly, and are mechanically distinct. Measurements with NCAM domain deletion mutants mapped the weaker bond to the Ig1-2 segment, and the stronger bond to the Ig3 domain. Finally, the quantitative agreement between the fragment adhesion and the strengths of both NCAM bonds shows that the domain deletions considered in this study do not alter the intrinsic strengths of either of the two bonds.



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Received for publication, April 12, 2005 , and in revised form, September 19, 2005.

But to answer the question of covalent vs ionic:

IONIC BONDS

Some atoms, such as metals tend to lose electrons to make the outside ring or rings of electrons more stable and other atoms tend to gain electrons to complete the outside ring. An ion is a charged particle. Electrons are negative. The negative charge of the electrons can be offset by the positive charge of the protons, but the number of protons does not change in a chemical reaction. When an atom loses electrons it becomes a positive ion because the number of protons exceeds the number of electrons. Non-metal ions and most of the polyatomic ions have a negative charge. The non-metal ions tend to gain electrons to fill out the outer shell. When the number of electrons exceeds the number of protons, the ion is negative. The attraction between a positive ion and a negative ion is an ionic bond. Any positive ion will bond with any negative ion. They are not fussy. An ionic compound is a group of atoms attached by an ionic bond that is a major unifying portion of the compound. A positive ion, whether it is a single atom or a group of atoms all with the same charge, is called a cation, pronounced as if a cat were an ion. A negative ion is called an anion, pronounced as if Ann were an ion. The name of an ionic compound is the name of the positive ion (cation) first and the negative (anion) ion second.

IONIC AND COVALENT BONDS

A bond is an attachment among atoms. Atoms may be held together for any of several reasons, but all bonds have to do with the electrons, particularly the outside electrons, of atoms. There are bonds that occur due to sharing electrons. There are bonds that occur due to a full electrical charge difference attraction. There are bonds that come about from partial charges or the position or shape of electrons about an atom. But all bonds have to do with electrons. Since chemistry is the study of elements, compounds, and how they change, it might be said that chemistry is the study of electrons. If we study the changes brought about by moving protons or neutrons, we would be studying nuclear physics. In chemical reactions the elements do not change from one element to another, but are only rearranged in their attachments.

A compound is a group of atoms with an exact number and type of atoms in it arranged in a specific way. Every bit of that material is exactly the same. Exactly the same elements in exactly the same proportions are in every bit of the compound. Water is an example of a compound. One oxygen atom and two hydrogen atoms make up water. Each hydrogen atom is attached to an oxygen atom by a bond. Any other arrangement is not water. If any other elements are attached, it is not water. H2O is the formula for that compound. This formula indicates that there are two hydrogen atoms and one oxygen atom in the compound. H2S is hydrogen sulfide. Hydrogen sulfide does not have the same types of atoms as water. It is a different compound. H2O2 is the formula for hydrogen peroxide. It might have the right elements in it to be water, but it does not have them in the right proportion. It is still not water. The word formula is also used to mean the smallest bit of any compound. A molecule is a single formula of a compound joined by covalent bonds. The Law of Constant Proportions states that a given compound always contains the same proportion by weight of the same elements.

See http://www.chemtutor.com/compoun.htm for a more indepth discussion of the subject.

(Old bad joke. I think I lost my electron. Are you sure? Yes, I'm positive.)

Answer 8

they can be ionic, covalent, or hydrogen bonds. they cannot, however be atoms simply held together by dipole moment or London forces.

Answer 9

it's called a 'formula unit' when it has ionic bonds

Answer 10

Hypothesis, as long as water binds......irrelevant