Why does Solder have a lower melting point than the parent metals

[YT2095]

Here: http://www.oksolar.com/led/led_color_chart.htm

 

this should clear up all the Gallium/LED color confusion, I used it myself some time ago in the "Fun with gallium" thread, whilst trying to make Light from Gallium Phosphide

[jdurg]

If you want the simple explanation about the lower melting point, just remember that the melting point of a substance is determined by how strong the intermolecular forces are between the individual atoms/molecules of the substance. Something like oxygen gas has a very low melting point because the simple Van der Waals forces keeping the oxygen together are very, very weak. Water, on the other hand, has a higher melting point because the hydrogen bonding it experiences keeps it together fairly tightly, but not tight enough to remain a solid at room temperature. Ionic compounds like NaCl have quite high melting points because the ionic charges on the components are very strong and keep the individual particles together. You need a lot of energy to overcome those intermolecular forces.

 

Metals tend to have high melting points as well because metallic bonding, the force keeping metals together, is a very strong intermolecular force. A few metals are exceptions to this, but most metals won't be liquid until elevated temperatures are reached. When you have an alloy, the presence of the different metals causes the intermetallic bonding to weaken. This weakening results in a lower melting point. A similar thing can be seen by mixing a lot of salt with some water. The melting point of the water will drop considerably.

[BenSon]

DQW you are an asset. see post 20.

 

~Scott

[EL]

If you want the simple explanation about the lower melting point' date=' just remember that the melting point of a substance is determined by how strong the intermolecular forces are between the individual atoms/molecules of the substance. Something like oxygen gas has a very low melting point because the simple Van der Waals forces keeping the oxygen together are very, very weak. Water, on the other hand, has a higher melting point because the hydrogen bonding it experiences keeps it together fairly tightly, but not tight enough to remain a solid at room temperature. Ionic compounds like NaCl have quite high melting points because the ionic charges on the components are very strong and keep the individual particles together. You need a lot of energy to overcome those intermolecular forces.

 

Metals tend to have high melting points as well because metallic bonding, the force keeping metals together, is a very strong intermolecular force. A few metals are exceptions to this, but most metals won't be liquid until elevated temperatures are reached. When you have an alloy, the presence of the different metals causes the intermetallic bonding to weaken. This weakening results in a lower melting point. A similar thing can be seen by mixing a lot of salt with some water. The melting point of the water will drop considerably.[/quote']

 

jdurg, your name is subtitled as a {Chemistry Expert}, and I have comments on what you said but please do not hold any "Grudge" or grudj.

The way you explained things gave the impression that the ionic bond energy of NaCl is stronger than the hydrogen bond of water, yet NaCl dissolves in water, which implies that water has the power to dissociate the ionic bond; isn't that a contradiction, or did you miss something?

Remember that the states of materials is an {Intermolecular} issue, while the ionic bond between sodium and chlorine is inside the molecule and not between molecules. Here, crystal lattice rules are dominant, and yes they are ionic but they are constantly {SHARED} over time. NaCl has a face-centred cubic crystal lattice structure.

This means that there is no one-on-one Na to chlorine bond association. To free any of the molecules thermally, is to expand the crystal to the threshold of crystal structure breakdown point (form a nano-powder) after which more heat is required to dissociate the nano-granules.

NaCl has a bond strength of roughly 412 kJ/mol, H-O bond has a strength of 427.6 kJ/mol; That is the hydrogen bond is obviously stronger than the NaCl ionic bond. However, in water, hydrogen bonds chelate between lone pairs of oxygen rings over time, and that is the reason behind water liquidity at room temperature.

 

As for metallic alloys of Tin and Lead (Sn_x.Pb_y); the Eutectic alloy has x = 63 and y = 37 as a ratio by weight per cent.

A eutectic alloy is a solid solution, and as a rule, all solutions have a lower phase-transition-temperature than the solute or the solvent due to heterogeneity.

Heterogeneity causes the vibration of the constituents to go out of phase faster and helps dissociation, while homogenous solids and liquids tend to vibrate in harmony, which dilates the transition of the phase.

 

While what you explained was generally correct, it is not that simple, especially when you include a liquid metal such as mercury being liquid at room temperature, while a non-metal like carbon has the highest melting point of all elements.

In phase transition temperature studies we cannot think in terms of molecules, but in terms of material supramolecular structure.

 

Kindest regards.

[YT2095]

Does carbon have a melting point? I thought it sublimes.

 

and isn`t Tungsten the element with the highest MP?

[EL]

Does carbon have a melting point? I thought it sublimes.

 

and isn`t Tungsten the element with the highest MP?

 

Check the Melting Point of Diamond on the scale here.

 

<http://www.fsref.com/Fatal/FEA00002.SHTML >

 

A sublimating diamond ring stone would drive women crazy.

[YT2095]

aha, it`s BP I was thinking of then, Tungsten is top of the list.

 

I never considered Diamond actualy, nice one

[EL]

And the BP of carbon is still third from top downwards.

Not many people know that because of fast air oxidation and CO2.

Yet another riddle is when we consider amalgams of mercury, where the alloy has a higher not lower melting point, and is even used in dental fillings, especially mercury-gold-amalgams.

[MetaFrizzics]

not to be boasting' date=' but ive done alot of soldering (not electronics, but mecanical, such as wierd things and metal art) and ive found that lead solder is crap. Its weak, poisonous, soft, and has a higher surface tension than all the other lead free things ive used. The ultimate solder ive found is silver solder (tin 96%; silver 3%; copper 1%)[/quote']Silver solder is the king of pipe joints, but the higher melting tempreature (430 degrees to over 1300 degrees F) make it rather prohibitive to use with electronics.

All those little junctions in semiconductor chips don't like heat too much. The less heat you use, the less chance you'll cook the chip.

I'm sorry. I have to agree with the 1st poster: Silver solder is king. For all discrete component soldering, for instance caps, resistors, inductors etc, Silver solder is safe and effective, and offers the best electrical connection possible. All my hi-fidelity tube (point-to-point wiring) power amplifiers I use only silver solder, and silver-plated wire. The result is incredible in terms of audio purity of sound, and reliability.

 

No one should be hand-soldering I.C. components unless they have to. You should either doing that by a wave-solder machine or using a socket-mount. You can do it with special heat-sink tools and soldering tips, and it works for repairs if you are skilled: but you need a delicate balance of proper wattage stations, low-temp solder and experience and care to hand-solder most Integrated Circuit components. Nowadays most heavily miniaturized chips are surface-soldered.

 

Any way, hand-soldering electronic connections with discrete components of reasonable size and scale: silver solder. Standard solder is crap, and low-temp solder isn't so good either.

[bobabot1]

Does anyone know where I could aquire a metal that's liquid at room temp? I'm a student so I have limited funds (read: broke)

 

If only Hg was non-toxic...