Science With Mr. Milstid

About 440BC, a Greek scientist named Democritus came up with the idea that eventually, all objects could be reduces to a single particle that could not be reduced any further.
He called this particle an atom, from the Greek word atomos which meant “not able to be divided.”
From this, the idea of the atom – the basic building block of all matter – was born.

While not exactly correct about the size of atoms, or the ability to be subdivided, Democritus discovered one of the most important “things” in science, the atom.
By definition, an atom is the smallest particle into which an element can be divided and still be the same substance. Atoms are the basis of chemistry. They are the basis for everything in the Universe. They are the basis for you! (Obviously, they are a little bit important.)

Our next stop in the history of atoms brings us all the way up to around 1700. By this point, scientists understanding of molecular composition of matter had grown considerably since Democitus’ time; they had figured out that elements combine together in specific ratios to form compounds. One scientist, John Dalton, wanted to know why.
He began to experiment with many different substances, and finally came to the conclusion that compounds come together in specific ratios because they are made of single atoms.
This was a breakthrough in the scientific community’s understanding of the role that atoms played in our world.
In 1803, Dalton came up with a theory about atoms:

1. All substances are made of small particles that can’t be created, divided, or destroyed called atoms.
2. Atoms of the same element are exactly alike, and atoms of different elements are different from each other. (So, atoms of gold are exactly like gold atoms, but different than aluminum atoms).
3. Atoms join with other atoms to make new substances.

For a time, Dalton’s theories were the scientific standard, but, by the end of the 1800’s, scientists had decided that, though much of what he had theorized was correct, new information they could observe about the way matter behaved proved some of Dalton’s theory wrong. So they changed atomic theory, step by step, until they reached the ideas we understand to be true today.

One major change to Dalton’s atomic theory was the discovery of electrons.
In 1897, a British scientist named JJ Thomson discovered small particles inside an atom – which means that atoms can be divided into even smaller parts.
Thomson used something called a cathode-ray tube to discover electrons, which he thought were spread throughout an atom like “plums in a pudding”.



Thus, we consider Thomson’s model of the atom the “plum pudding” model.

 


 
In 1909, a scientist named Ernest Rutherford decided to test the Thomson theory, and designed an experiment to examine the parts of an atom.
He aimed a beam of small, positively charged particles at a sheet of gold foil with a special coating on the back. This coating glowed when hit by the positively charged particles, so Rutherford could see where the particles were going after they hit the gold sheet they were aimed at.
He began with the idea that atoms were soft blobs of matter with electrons spread throughout them, but when he saw the way some of the particles he was shooting at his machine bouncing around in different directions, he realized that atoms must be made differently.
If they were bouncing around and reflecting, then they must be much more dense than he originally thought.

 


 
Following Rutherford’s experiments, Niels Bohr proposed in 1913 that electrons move around the nucleus of an atom in specific paths, on different levels of energy.
He proposed that there were several layers of electrons surrounding a nucleus, all of which travel around in an orbit.



By now, we have come to understand that electrons do not, in fact, travel in specific paths or orbits around the nucleus of an atom.
Instead, they move randomly around the nucleus, with no specific pattern or path, and they do it in a general range of area called an electron cloud (the area where an electron is likely to be found around a nucleus).

Tags: Atomic History, Atomic Structure
Posted in Atomic Structure, Matter & Properties of Matter, Physics & Physical Science