5 ms·
“Daltons are used to measure something very low in mass” Why not just use nanograms or picograms?
by b34r 6y ago
“Daltons are used to measure something very low in mass”
Why not just use nanograms or picograms?
- b34r 6y agoApparently picograms are still orders of magnitude bigger and thus not useful for this type of measurement. Science! Looking further into it, yoctagrams or zetograms would be small enough to express the measurement. I suspect daltons are used because they’re pegged to a 1/12 of a carbon atom and that makes the math easier to reason about or something like that.
- deleted 6y ago[deleted]
- dmurray 6y agoYeah, one Dalton = one neutron or one proton [0], so it's a convenient unit if you're literally adding up atomic weights to find the weight of a single molecule. [0] This is true for chemists, but not for physicists, who pay more attention to the mass defect rounding error.
- contravariant 6y agoTo expand on that, for physicists Carbon-12 is exactly 12 daltons also denoted 12 Da or 12 u. All other isotopes deviate slightly from a whole number of daltons. If I recall correctly the number of nucleons minus the daltons continues to decrease until you get to iron, which has the lowest nuclear binding energy, after which it continues to increase again (although there's some variation between isotopes so this is more of a general trend).
- dmurray 6y agoAnd that's why you can have nuclear power either from combining really small atoms (fusion) or splitting big ones (fission) but nobody would propose a nuclear reactor that runs on iron?
- zokier 6y ago1 Da = 1.66 yg (yoctograms), approximately. So that kinda works out. Another unit that is occasionally used for atomic scale masses is eV, as in electronvolt. 1 Da = 0.93 GeV
- b34r 6y agozeptograms
- deleted 6y ago[deleted]
- twic 6y agoA dalton has two nice properties. One is that a hydrogen atom weighs one dalton, and a carbon atom twelve etc, so a mass in daltons immediately tells you roughly how big a molecule is in atomic terms. 100 Da is a small molecule, 1 kDa would be a peptide or macrolide or something, 10 kDa is a small protein, 100 kDa is a big protein, etc. The other is that a dalton is a gram per mole, so if you know the mass of a molecule in daltons, you can easily convert between mass and concentration at macroscopic scale. So, glucose is 180 Da, you can dissolve 180 g of it in 1 litre of water to make 1 molar solution. These properties are really the same property, because of how the mole is defined, but that property is useful in two quite different ways.
- b34r 6y agoThanks, that was a really clear explanation!