John Dalton's Atomic Theory

For more than 2000 years after the birth and sustenance of this belief, nobody did anything to contribute to the explorations that the Greeks had started into the nature of matter. The people did not begin to revisit and question this theory again until the early 1800s.

In the 1800s, John Dalton, an English chemist, began his pursuit for the truth behind the divisibility of atoms. He performed various chemicals experiments that showed that matter, indeed, seemed to consist of elementary lumpy particles (atoms). Although he did not know about their structure, he was quite certain that this evidence would lead to something fundamentally significant about the discovery and divisibility of atoms and matter. He postulated the following-

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Most of the alpha particles went straight through the foil. Only a few occasional alpha particles veered sharply from i original path, sometimes bouncing straight back from the foil! Rutherford reasoned that they must get scattered by tiny bits of positively charged matter. Most of the space around these positive center had nothing in them. He thought that the electrons must exist somewhere within this empty space. Rutherford thought that the negative electrons orbited a positive center in a manner like the solar system where the planets orbit the sun.Rutherford knew that atoms consist of a compact positively charged nucleus, around which circulate negative electrons at a relatively large distance. The nucleus occupies less than one thousand million millionth of the atomic volume, but contains almost all of the atom's mass. If an atom had the size of the earth, the nucleus would have the size of a football stadium.Not until 1919 did Rutherford finally identify the particles of the nucleus as discrete positive charges of matter. Using alpha particles as bullets, Rutherford knocked hydrogen nuclei out of atoms of six elements: boron (B), fluorine (F), sodium (Na), aluminum (Al), phosphorus (P) and nitrogen (N). He named them protons, from the Greek for 'first', for they consisted of the first identified building blocks of the nuclei of all elements. He found the protons mass at 1,836 times as great as the mass of the electron.

But there appeared something terribly wrong with Rutherford's model of the atom. The theory of electricity and magnetism predicted that opposite charges attract each other and the electrons should gradually lose energy and spiral inward. Moreover, physicists reasoned that the atoms should give off a rainbow of colors as they do so. But no experiment could verify this