From cookies to solar systems
As you'll recall, since Dalton came up with a modern atomic theory, things started to move. J.J. Thomson was the first to rock the boat with his discovery of the electron through experimentation with cathode ray tubes. This led us to accept the chocolate chip cookie atomic theory, which is both smart and delicious!
Of course, things wouldn't stay quite for long. With the discovery of the electron, people started to look into it and the atom as a whole much more deeply, and it only a matter of time before things began to get funky.
Milikan's
oil drops
It was 1909, 5 years after Thomson published his theory, when Robert Millikan conducted an experiment which would finally solve an answer Thomson left unanswered. As you can probably remember, Thomson discovered the charge-to-mass ratio of an electron, but what was the charge of an electron, or the actual mass? This was still up for grabs.
And Millikan grabbed. He charged tiny droplet of oil with a negative charge, and used a uniform electric field to balance the electric force pushing the droplet up and gravity pushing it down. Then, using force analysis, he could calculate the charge on the droplet. He repated this experiment over and over again, and found out the smallest common factor of all results- 1.602×10 ^ - 19 C. This is the charge of an electron. From here, he simple used Thomson's analysis to find the mass- 9.11×10^-31 kg.
Goldstein
and Protons
After Thomson discovered the electron, a guy named Goldstein reasoned that atoms must have positive particles that balance out the charge and result in a neutral atom. He discovered "canal rays", which were basically rays moving in the opposite direction to the cathode rays of electrons. This rays were really positive ions, but Goldstein figured they have to be the positive particles we now call protons.
Nobody listened to Goldstein anyway. It would take some time before protons would be accepted. Until then, somebody else would come in and do something bigger and louder, and this guy would be called Rutherford.
The
father of nuclear physics- Rutherford
Rutherford, who was actually Thomson's student, is widely known for the Gold-foil experiment. This experiment was simple- you take a really thin foil of gold, a few atoms thick, and bombard it with positively charged alpha particles. According to the cookie model of the atom, the particles should pass through undisturbed.
The real results were shocking- while most particles passed through undisturbed, a few were heavily deflected. In 1911, Rutherford finally published a solution to this odd result- the cookie model is wrong. Atoms aren't made of electrons with positive dough around them.
Based partially on work by Japanese physicist Gantaro Nagaoka, Rutherford's model introduced the nucleus- a centre where the majority of the atom's mass and charge is located. Most of the atom is in fact empty space, vacuum. This model of the atom is pretty much what we use today: a nucleus with orbiting electrons around it. As you can see though, the basis behind this is complex and fascinating.
And there's still more to go. While this model closely resembles our modern concepts, it would take the introduction of quantum physics to introduce a more complete model that gets closer to the real atom…
To be continued in Part 5
