Download The Scientists - WordPress.com

The Scientists
OF ATOMIC THEORY
Democritus

Democritus came up with “atomos” after wondering what would
happen if you cut a piece of matter into smaller and smaller pieces.
He thought that a point would be reached where matter could not
be cut into smaller pieces. These “indivisible” pieces would be the
early “atomos” or atoms. (atomos: uncuttable or indivisible)

Again, Thanks Aristotle.
Dalton

Dalton did lots of experiments that provided evidence for atoms.

He studied the pressure of gases, concluding that gases must consist
of tiny particles in constant motion.

He was a teacher who just did research in his spare time. He
developed much of the atomic theory that we still use today.

Dalton’s Atomic Theory consisted of 3 main ideas:
1.
All substances are made of atoms. Atoms are the smallest particles of
matter. They cannot be divided into smaller particles. They cannot be
created or destroyed.
2.
All atoms of the same element are alike and have the same mass.
Atoms of different elements are different and have different masses.
3.
Atoms join together to form compounds. A given compound always
consists of the same kinds of atoms in the same ratio.
Thomson

Thomson was interested in electricity. He did experiments in which
he passed an electric current through a vacuum tube. (Like modern
batteries.)

His experiments showed that an electric current consists of flowing,
negatively charged particles.

This was important because most scientists of this time thought of
electricity in terms of rays, like rays of light, which would be positive
rather than negative.

Thomson’s experiments showed that negative particles are all alike,
and they are all smaller than atoms.

They couldn’t be fundamental units of matter because of their
similarities.
Rutherford
Rutherford discovered that some elements give off positively charged
particles. He named them alpha particles. He used these alpha
particles to study atoms.
 He aimed a beam of alpha particles at a very thin sheet of gold foil.
Outside the foil, he placed a screen of material that glowed when
alpha particles struck it.


If Thomson’s plum pudding model were correct, the alpha particles would
have deflected a little as they passed through the foil.
Most of the particles passed straight through the foil as though they
were moving through empty space.
 Rutherford concluded that all the positive charge of an atom is
concentrated in a small central area. He called this area the nucleus.
 Where Thomson discovered electrons, Rutherford discovered protons
and the nucleus. He predicted the existence of neutrons, but never
found them. But in 1932, his protégé, James Chadwick, did find them.
They were in the nucleus with the protons, just where Rutherford
predicted they’d be.

Bohr

Bohr’s research focused on electrons. He discovered evidence that
the orbits of electrons are located at fixed distances from the
nucleus, rather than Rutherford’s hypothesis that the electrons just
moved in random paths.

The level with the least energy is the one closest to the nucleus. As
you go farther and farther from the nucleus, the levels have more
and more energy. If an atom absorbs energy, some of the electrons
can “jump” to a higher energy level.
Heisenberg and the Electron Cloud

The model we use today is called the “Quantum Mechanical
Model” or more simply the “electron cloud model.”

Physicists discovered that electrons do not travel in fixed paths. They
found that electrons only have a certain chance of being in any
particular place.

The electrons have wave-like properties that lets them exist only at
certain distances from the nucleus. Like rungs of a ladder; you can be
on one rung or another, but not in the space between the rungs.
And then…

https://youtu.be/thnDxFdkzZs crash course