Name: 【TED-Ed】The 2,400-year search for the atom - Theresa Doud
Uploaded: 2014-12-26T03:09:32.000Z
Duration: 5 min 23 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

have in common  with Nobel Prize-winning scientists?

Although they are separated  over 2,400 years of history,

each of them contributed  to answering the eternal question:

It was around 440 BCE  that Democritus first proposed

that everything in the world  was made up of tiny particles

And he even speculated  that they vary in size and shape

He called these particles "atomos," Greek for indivisible.

His ideas were opposed by the more popular philosophers of his day.

Aristotle, for instance, disagreed completely,

stating instead that matter  was made of four elements:

Atoms would remain  all but forgotten until 1808,

when a Quaker teacher named John Dalton  sought to challenge Aristotelian theory.

Whereas Democritus's atomism had been purely theoretical,

Dalton showed that common substances always broke down into the same elements

were combinations of atoms  of different elements,

that could neither be created  nor destroyed.

Though he received  many honors for his work,

as a Quaker, Dalton lived modestly  until the end of his days.

Atomic theory was now accepted  by the scientific community,

would not come  until nearly a century later

with the physicist J.J. Thompson's  1897 discovery of the electron.

In what we might call  the chocolate chip cookie model of the atom,

he showed atoms as  uniformly packed spheres of positive matter

filled with negatively charged electrons.

Thompson won a Nobel Prize in 1906  for his electron discovery,

but his model of the atom  didn't stick around long.

This was because he happened  to have some pretty smart students,

who would become known  as the father of the nuclear age.

While studying the effects  of X-rays on gases,

Rutherford decided  to investigate atoms more closely

by shooting small, positively charged  alpha particles at a sheet of gold foil.

the atom's thinly dispersed  positive charge

would not be enough  to deflect the particles in any one place.

The effect would have been  like a bunch of tennis balls

But while most of the particles  did pass through,

suggesting that the foil was more  like a thick net with a very large mesh.

Rutherford concluded that atoms  consisted largely of empty space

while most of the mass  was concentrated in the center,

The alpha particles  passed through the gaps

but bounced back from the dense,  positively charged nucleus.

But the atomic theory  wasn't complete just yet.

In 1913, another of Thompson's students  by the name of Niels Bohr

Drawing on earlier work  by Max Planck and Albert Einstein

he stipulated that electrons  orbit the nucleus

able to jump from one level to another, but not to exist in the space between.

Bohr's planetary model took center stage,

but soon, it too encountered  some complications.

Experiments had shown that rather than  simply being discrete particles,

electrons simultaneously  behaved like waves,

not being confined  to a particular point in space.

And in formulating  his famous uncertainty principle,

Werner Heisenberg showed  it was impossible to determine

both the exact  position and speed of electrons

The idea that electrons  cannot be pinpointed

but exist within  a range of possible locations

gave rise to the current  quantum model of the atom,

a fascinating theory  with a whole new set of complexities

whose implications  have yet to be fully grasped.

Even though our understanding  of atoms keeps changing,

so let's celebrate  the triumph of atomic theory

As electrons circling an atom  shift between energy levels,

they absorb or release energy in the form of specific wavelengths of light,

resulting in  all the marvelous colors we see.

And we can imagine Democritus  watching from somewhere,

he turned out  to have been right all along.