Reading a SciFi book that mentions how expensive a space elevator is compared to rockets.

It got me wondering, what’s the longest single molecule?
Which brings in the issue of alternative definitions of “molecule”.

• A carbon nanotube is a single molecule, but how does the maximum length of that compare to other large molecules such as DNA and large single molecules of polymers (such as nylon, aramid etc.)
• If I loosen the definition of “molecule” to include single crystals with covalent bonding, what is the longest there?
• If I loosen the definition of molecule still further to allow covalently bonded continuous lengths of glasslike ceramics, what is the longest there?
• If I loosen the definition still more to include single crystal metals, what is the longest there?

Could a carbon fibre be considered a single molecule?
Could a single continuous metal wire be considered a single molecule?

with such loose definitions you’ll end up including degenerates soon

mollwollfumble said:

• If I loosen the definition still more to include single crystal metals, what is the longest there?

The turbine blades in a jet engine are a single crystal. There’s a good video on how large Rolls-Royce 747 jet engines are made, and the section on the turbine is here
The bit that may well frighten you though, is here :)

Oh darn, completely lost the post to this thread I’d been working on for an hour.

A single DNA molecule of the flower Paris japonica is close to 2 metres long. A single DNA of the marbled lungfish ought to be longer than this – at a guess roughly 2.5 metres long.

That makes it longer than the longest carbon nanotube at 0.55 metres long.

Crystals can be covalent (like molecules), ionic, metallic, or hydrogen bonded.

mollwollfumble said:

Oh darn, completely lost the post to this thread I’d been working on for an hour.

A single DNA molecule of the flower Paris japonica is close to 2 metres long. A single DNA of the marbled lungfish ought to be longer than this – at a guess roughly 2.5 metres long.

That makes it longer than the longest carbon nanotube at 0.55 metres long.

Crystals can be covalent (like molecules), ionic, metallic, or hydrogen bonded.

Monofilament nylon is easily available in lengths at least up to 55.5 km. But is this a single molecule?

Optic fibre glass is easily available as a strand more than 100 km long between repeaters for submarine cables.

A single optical fibre reaching 10,000 km from Sydney to Perth without regeneration has been reported, It’s in the Guinness book of records. But I don’t know if that means it’s a single piece of glass. https://exchange.telstra.com.au/evolved-optical-network-record-breaking/ It may be a single length of glass fibre over the whole distance.

Largest Single crystal:
Covalent bonding, 6.1 metres, quartz, natural.
Ionic bonding, 11 metres, gypsum, natural.
Metallic bonding, ~0.2 metres?, jet turbine.
Hydrogen bonding, 0.38 metres, snowflake, natural.

mollwollfumble said:

Largest Single crystal:
Covalent bonding, 6.1 metres, quartz, natural.
Ionic bonding, 11 metres, gypsum, natural.
Metallic bonding, ~0.2 metres?, jet turbine.
Hydrogen bonding, 0.38 metres, snowflake, natural.

Other sources of long crystals (and molecules) are directional cooling (including continuous casting) and wire drawing. These have multiple crystals side by side, making it really difficult to know just how long the individual crystals (and molecules) are.

For example, steel wire, copper wire, nylon monofilament, clear ice.

From polarising photomicrographs of nylon monofilament, all I can say is that crystals up to 0.08 mm across and in excess of 0.1 mm long (they extended off the edge of the picture) have been observed.

Anyone on the forum have a polarising microscope to look at these?

Though of course gypsum has ionic bonds AND covalent bonds

dv said:

Though of course gypsum has ionic bonds AND covalent bonds

maybe he’s arguing that they’re just bonds, and there’s always a bit of ionic and covalent character

SCIENCE said:

dv said:

Though of course gypsum has ionic bonds AND covalent bonds

maybe he’s arguing that they’re just bonds, and there’s always a bit of ionic and covalent character

I hadn’t thought of that.

The covalent bonding of just one sulfur to four oxygen atoms hardly makes it a giant molecule.

I’m really commenting on (or asking about?) alternative definitions of the word “molecule”.

mollwollfumble said:

SCIENCE said:

dv said:

Though of course gypsum has ionic bonds AND covalent bonds

maybe he’s arguing that they’re just bonds, and there’s always a bit of ionic and covalent character

I hadn’t thought of that.

The covalent bonding of just one sulfur to four oxygen atoms hardly makes it a giant molecule.

I’m really commenting on (or asking about?) alternative definitions of the word “molecule”.

Would polyethylene be considered a molecule?

This is a semantic discussion. Not trying to dismiss it but basically these demarcation disputes don’t tend to be enlightening.

> It got me wondering, what’s the longest single molecule?

Silk?

Silk is a protein that is incrementally solidified from one end. So, may it contain single protein molecules in parallel along most of the entire strand?

One continuous strand of silk can be up to 1,000 metres long.

Tamb said:

Would polyethylene be considered a molecule?

Yes. How long can a molecule of polyethylene be? Let’s see. “UHMWPE has a molecular weight up to 6 million Daltons”. That’s 0.9 metres, which is longer than the longest carbon nanotube.

mollwollfumble said:

> It got me wondering, what’s the longest single molecule?

Silk?

Silk is a protein that is incrementally solidified from one end. So, may it contain single protein molecules in parallel along most of the entire strand?

One continuous strand of silk can be up to 1,000 metres long.

Tamb said:

Would polyethylene be considered a molecule?

Yes. How long can a molecule of polyethylene be? Let’s see. “UHMWPE has a molecular weight up to 6 million Daltons”. That’s 0.9 metres, which is longer than the longest carbon nanotube.

Thanks, I suspected it would be a contender.