Discovery of Electrons and Protons
For many centuries, we didn't know what matter is made of.
Democritus, a Greek philosopher, first came up with the idea that matter is made of very small particles.
He proposed that if we cut something over and over again, we would come to a particle that cannot be cut any more.
He called this particle 'atomos', which means uncuttable.
We derive the word 'atom' from this Greek term.
Many thousand years later, we still did not have a proper understanding of what matter is made of or what atoms look like.
In 1800's, John Dalton was the first to give a scientific explanation for Democritus’ theory.
He showed that all matter consists of tiny particles, which are called atoms.
But he still hadn't explained the structure of an atom or what atoms are made of.
A major breakthrough happened in 1886 when E. Goldstein discovered positively charged rays.
His findings were based on experiments with gases. He called the positively charged rays as canal rays.
The significance of this discovery is that it proved that matter contains positive charges in it.
A few years later, in 1897, J. J. Thomson discovered that atoms contain negatively charged particles.
He called them 'corpuscles'. 'Corpuscles' were later renamed electrons.
Thomson also made another important observation.
He showed that the negatively charged particles are equal in magnitude to positive charges in the atom. So, atom is neutral.
Later, in 1899, Ernest Rutherford experimentally showed that the positive charges are not spread across the atom.
Instead, positive charges are localised at the centre, called nucleus, and most of the atom is empty space.
Ultimately, Rutherford discovered that the positive charges are in fact positively charged particles, which he named 'protons'.
So, atoms were shown to have two subatomic particles, positive protons and negative electrons.
Protons are denoted as p
and electrons are denoted as e
The charges of these particles are equal in magnitude. So, charge of proton is taken as +1 and that of electron is -1.
The mass of the proton was found to be 2000 times that of the electron.
For convenience, we represent the mass of the proton as 1 unit and that of the electron as negligible.
With more discoveries, the structure of atom became clearer to us. But, there's still more to learn about it than we already know.
Early thinkers like Democritus and later scientists like Dalton proposed that matter is made of tiny particles called atoms.
Goldstein discovered that matter consists of positive charges based on his experiments with canal rays.
Thomson discovered that atoms contain negatively charged particles called electrons equal in magnitude to positive charges.
Rutherford showed that an atom consists of a nucleus containing positive charges. Most the atom is empty space.
It was later found that nucleus contains positively charged particles called protons.
) and electrons (e
) are subatomic particles present in an atom.