Ionic bond

Properties of ionic substance

Can anyone tell me why Ionic substances don't conduct electricity when they are a solid but do conduct electricity when molten or in aqueous solution??

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For something to conduct electricity,
it has to contain "charge carriers" that are free to move inside the substance.

A molten ionic substance is composed of +ve cations and -ve anions, both of which are "charge carriers" and are free to move around.

However, a solid ionic substance is also composed of +ve cations and -ve anions, but the difference is that they are NOT free to move around... instead, they locked in a solid ionic lattice shape, and so can't conduct electricity.

In aqueous solution, the +ve cations and -ve anions are "solvated" (surrounded by a sheath of water molecules) and these solvated ions are charge carriers and are free to move around.

Does that goes the same for covalent substance?
I read that pure covalent substance don't conduct electricity even if they are solid or liquid, y?

No, a covalent substance generally won't conduct electricity whether it
is solid or liquid, because it has no charge carriers inside it.

It just has neutral molecules inside it.
The neutral molecules are fixed in a rigid lattice in the solid.
In the liquid, the neutral molecules are free to move around - but
because they are neutral, having no net electric charge, they
won't move in response to an electric field or electric potential.

Ummm could u explain what charge carriers are?
and y they have neutral molecule? plz
I don't get y ionic and covalent is so different...

"Charge carriers" are anything that can, erm, "carry" and electric "charge" around -)

Examples are
free electrons
positive cations
negative anions

(when a substance contains free charge carriers,
and you apply an electric potential across that substance,
the charge carriers move in response to the potential.
This is movement of charge carriers is what we call "electric current")

Covalent substances *are* substances which are composed of neutral molecules. It makes no sense to ask "why". If they weren't composed of neutral molecules, then we wouldn't call them covalent substances -)

Hey! i knew that metal ion is positive and non-metal ion is negateive.they should be neutral after ionic bond.then why you said that they have either positive charge or nagative charge?

No, you are confused, mr noidea

the overall bulk solid or liquid is neutral in an ionic substance
(cos the gazillions of +ve cations and -ve anions all balance each other)

But the ions themselves ARE postively and negatively charged.

oh..

but the ions are bonding together ...then how can it conduct electricity...

Ionic compounds conduct electricity only if they are liquid or dissolved in water.

No you are confused.

(First of all, let us bear in mind that the "ionic model" is a made up, simplified version of what "really" happens ;-)

But anyway, according to the "ionic model",
the ions are not "bonding together" in the sense that there's any physical connection between any of them.

All that's happening is an "action at a distance" - in the solid, the cations and anions are actually all just sitting there stationary, at fixed points in an ionic lattice. Ions are pretty tiny things -) You could use X-ray diffraction to investigate what the actual inter-nuclear distances are ... but as a rough guide, if the ions were the size of footballs, I think they'd all be several hundred yards away from each other.
Electrostatic forces of attraction and repulsion exist between all the ions, acting at a distance between them, keeping them stuck in place.

If you heat up the subtance enough, so that it melts, the ions now have enough kinetic energy so they're not stuck in their places - they're free to whizz around in response to gravity (so the liquid will flow to take the shape of a container) or in response to electric potential (so the ions will flow making an electric current). (Even in the liquid though, the ions are still not "touching" - they'd be whizzing around past enough other, with electrostatic forces attracting/repelling them.)

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