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6 Times Scientists Were Wrong About the Periodic Table
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“Water. Earth. Fire. Air.” Aristotle may not have had a poster of the periodic table
on his bedroom wall growing up.
But he sure did have an idea about what everything on Earth was made of.
That idea was very, very wrong, of course,
even if it did help spawn a beloved television series.
But over the following millennia,
scientists slowly worked things out.
By the time Dmitri Mendeleev published his original version of the periodic table,
in 1869, there were 63 elements that scientists knew
made all the matter we can see, touch, and so forth.
Part of that was thanks to advances in scientific theory,
like Dalton’s concept of the atom.
Part of it was thanks to advances in scientific methods and technology.
But the path from 63 to the current 118 elements was not straightforward.
In fact, there are many times scientists thought they had discovered a new element,
but didn’t.
So many in fact, you could make a SciShow List Show about it…
[intro jingle]
Here’s a lie that your teacher might have told you when you were young:
“Sunlight is made up of all the colours of the rainbow.”
And by “lie ”, I mean it’s so close to true
almost no one is going to call that teacher out.
Except for when it actually matters.
Like right now.
In the early 1800s,
the German glassmaker Joseph von Fraunhofer
split sunlight up into its constituent colors
using a device he invented called a spectroscope.
And he found 574 dark lines in the otherwise full rainbow.
In other words, a bunch of colors were missing.
These lines turned out to be super important
for chemistry, physics, astronomy, and optics.
Fraunhofer’s discovery was, and remains, a pretty big deal.
He was the first to document these spectral absorption lines,
caused by atoms absorbing specific amounts of energy
from light that’s passing through.
Because when you’re dealing with light, energy corresponds to wavelength…
that is, color.
Then the 1860s, some other German scientists…
including Robert Wilhelm Bunsen of “bunsen burner” fame…
found that absorption lines had not-at-all-evil twins
called spectral emission lines
that show up when you split up the light coming from an element
when it’s burning.
Both emission and absorption lines
are the result of an atom’s electrons jumping between energy levels.
When it’s emission, the electron is emitting that energy,
so it’s dropping down some number of levels.
When it’s absorption, it’s the opposite.
The exact amount of energy,
and therefore the exact color of the light,
depends on several factors, including how many electrons are involved,
and which levels they’re jumping between.
Both of these lines act like chemical fingerprints,
because each atom has a unique set of lines that they produce.
So element hunters started using spectroscopes
to split light from all sorts of places
to find unique new fingerprints, and therefore elements.
Remember that this is right around when Mendeleev
is coming up with his periodic table.
He’s arranged the known elements according to atomic weight,
but he realised that there are repeating patterns of properties.
When he mapped it all out,
there were actually gaps where unknown elements might be.
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