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The Atomic Theory
Transcript of The Atomic Theory
By : Hyun Ji Song
design by Dóri Sirály for Prezi
In 440 BCE, Democritus, a Greek philosopher thought that if you cut something in half over and over again, he thought that you would eventually end up with a particle that could not be broken down or divided any farther. Democritus called that particle an atom, the word from atomos meaning "not able to be divided".
Aristotle and Atoms
An another Greek philosopher named Aristotle disagreed with Democritus's ideas. Since Aristotle had a strong influence on people's minds, many thought that you would never end up with a particle that could not be broken down any farther.
But we know now that Aristotle was actually wrong. Atoms make up matter. Atoms are the smallest particles in which elements could be broken down but keep the same its identity.
John Dalton's Theory
Scientists has learned that elements combine in a certain ratio to form compounds by the late 1700s. A British chemist and a schoolteacher named John Dalton wanted to know why. He experimented many times and his results concluded that elements combine in certain proportions because they're made up of single atoms. He published his theory in 1813 and his theories were :
All substances are made up of atoms.
Atoms of the same element are exactly the same and atoms of different elements are different.
Atoms join with other atoms to form new substances.
In 1897, J. J. Thomson, a British scientist, proved wrong to Dalton's theory. He discovered that there were small particles inside the atom. That meant the atom could be divided into father parts. He experimented with a cathode-ray tube to prove his discovery. Thomson concluded that the negatively charged particles are present in every atom and they are now called electrons.
The Modern Atomic Theory
Many 20th century scientists added the current knowledge of atoms. Erwin Schrödinger, an Austrian physicist, and Werner Heisenberg, a German physicist made a great contribution. They explained the nature of electrons further and discovered that there are regions in the atom that electrons are likely to be found since they have no definite paths. They are called electron clouds.
Toward the end of the 1800s, scientists agreed with Dalton's theory. But as new information was discovered, Dalton's theory was changed into the modern atomic theory.
Thomson created a new model of an atom after learning the existence of electrons. The model was sometimes called the plum-pudding model named after a popular dessert during the day. You might call his model chocolate chip ice-cream model today.
1909, a student of Thomson named Ernest Rutherford designed an experiment to study the parts of an atom. Rutherford started with Thomson's idea that atoms are soft "blobs" of matter and expected the particle to pass right through the gold but there were some particles the deflected. Some even bounced back! It really was a surprising result.
In 1911, Rutherford edited the atomic theory and made a new model. He introduced that in the center of an atom is a dense, positively charged nucleus. Rutherford also calculated that the diameter of the nucleus is 100,000 times smaller than the diameter of the gold atom.
Niels Bohr, a Danish scientist who worked with Rutherford, studied the way atoms react to light. His results led him that electrons move in a certain path or energy levels. Electrons can jump from one energy level to the other. Bohr's model became very valuable but the atomic theory still had room for improvement.