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Topic: Metallic bonds and applications of metal  (Read 3424 times)

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Offline Technicalhuman

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Metallic bonds and applications of metal
« on: October 03, 2013, 01:25:20 AM »
Metals have metallic bonds which are the forces of attraction between the delocalized electrons and the positive nucleus. So when we apply force on a layer of metal it will just slide over as the valance electrons do not belong to any particular metal atom.

I don't quite understand this statement. Metals can be drawn into wires. While doing so, the metal is torn and again because the valence electrons do not belong to any positive ions, the metal can just break into two pieces? Again there would be some resistance where would this come from?

So I'm not very sure when the metallic bond is broken. When we melt it, are some of the, broken? What happens to the delocalized electrons and metal ions then? And for boiling all the metallic bonds should be broken. So again where do the valance electrons and metal ion go?

I believe they are different from ionization because I've seen equations like this Metal(g) :rarrow: metal+ (g)+e
But then in this case this would imply that during boiling, the delocalized electrons go back into the metal ion. Which seems funny because the metallic bonds between that valence electron should be broken not joined together.

Thanks so much for the help :)

Offline Enthalpy

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Re: Metallic bonds and applications of metal
« Reply #1 on: October 03, 2013, 06:51:05 PM »
Gaseous metal uses to consist of individual neutral atoms ("uses to" because there must be some exceptions). So when a metal sublimates or evaporates, ions separate from the metal together with the proper number of electrons to be neutral.

Deforming a metal doesn't need to break any bond... but it does need to pass some ions by others, which is difficult. In fact, deformation never happens with a force that cleaves the crystal and moves an ion plane versus an other.

First, temperature does most work; the force only makes the deformation happen preferentially in one direction, while temperature alone would do it randomly and symmetrically.

Then, deformation happens at special sites in the crystal that have already a stacking fault, called a dislocation. At the pre-existing dislocation, an atom has neighbours at imperfect positions, and this imperfection can travel easily - much more easily than a perfect stacking.
http://en.wikipedia.org/wiki/Dislocation

Metallurgy is badly complicated - so much that it can explain anything and its opposite equally well, to my opinion - but often, pure metals are very soft; alloying them is generally said to hinder the movements of dislocations, and this makes alloys harder.

Offline Technicalhuman

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Re: Metallic bonds and applications of metal
« Reply #2 on: October 05, 2013, 09:30:40 AM »
Gaseous metal uses to consist of individual neutral atoms ("uses to" because there must be some exceptions). So when a metal sublimates or evaporates, ions separate from the metal together with the proper number of electrons to be neutral.

Deforming a metal doesn't need to break any bond... but it does need to pass some ions by others, which is difficult. In fact, deformation never happens with a force that cleaves the crystal and moves an ion plane versus an other.

First, temperature does most work; the force only makes the deformation happen preferentially in one direction, while temperature alone would do it randomly and symmetrically.

Then, deformation happens at special sites in the crystal that have already a stacking fault, called a dislocation. At the pre-existing dislocation, an atom has neighbours at imperfect positions, and this imperfection can travel easily - much more easily than a perfect stacking.
http://en.wikipedia.org/wiki/Dislocation

Metallurgy is badly complicated - so much that it can explain anything and its opposite equally well, to my opinion - but often, pure metals are very soft; alloying them is generally said to hinder the movements of dislocations, and this makes alloys harder.

Hi enthalpy thanks for the reply

When we just heat up a metal such that it melts, I thought the metallic bond would be broken and since the metallic bond is the force of attraction between the valence electrons and the positive cations. So how would the gaseous metal remain neutral?

Thanks so much for the help

Offline Enthalpy

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Re: Metallic bonds and applications of metal
« Reply #3 on: October 05, 2013, 10:40:06 AM »
A few hints:
- Liquid metals conduct electricity
- Separate ions and electrons is extremely difficult. At 3500K for instance, the proportion of ions is minute.
- Metal gases are made of neutral atoms (possibly atoms clusters? Must exist for a few metals, I didn't check)
- When a metal gas condenses, it just reorganizes its electrons. The electrons keep close to the nuclei all the time.

More generally, you encouter extremely few ions under normal conditions. It happens in solvents where positive and negative charges can be very few molecules apart because the solvent molecules help it through their dipole moment.

The rest of time, changes of states and chemical reactions occur between neutral reactants, where the atoms are already arranged in molecules. Some already favourable bonds break, others slightly more favourable are built.

Offline Technicalhuman

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Re: Metallic bonds and applications of metal
« Reply #4 on: October 05, 2013, 10:45:11 AM »
A few hints:
- Liquid metals conduct electricity
- Separate ions and electrons is extremely difficult. At 3500K for instance, the proportion of ions is minute.
- Metal gases are made of neutral atoms (possibly atoms clusters? Must exist for a few metals, I didn't check)
- When a metal gas condenses, it just reorganizes its electrons. The electrons keep close to the nuclei all the time.

More generally, you encouter extremely few ions under normal conditions. It happens in solvents where positive and negative charges can be very few molecules apart because the solvent molecules help it through their dipole moment.

The rest of time, changes of states and chemical reactions occur between neutral reactants, where the atoms are already arranged in molecules. Some already favourable bonds break, others slightly more favourable are built.

Hi enthalpy thanks again for the reply.

But that would indicate that the bond between the positive Ion and negative electron isn't broken which I thought is the case during boiling? So what actually goes on to seperate each atom during boiling since the electron and positive ion doesn't get separated?

Thanks again for the help

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