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In our previous discussions, we explored how atoms were considered the fundamental, indivisible building blocks of matter, as proposed by John Dalton. However, by the end of the 19th century, scientists faced a major challenge: to truly understand the structure of the atom and explain its properties. This quest led to observations that would overturn the idea of the atom as an indivisible particle, revealing a fascinating world of even smaller constituents within.

One of the first clues that atoms were not indivisible came from studying static electricity and how different substances conduct electricity. Have you ever rubbed a comb through dry hair and noticed it attracts small pieces of paper? Or rubbed a glass rod with silk and watched it attract an inflated balloon? These simple activities demonstrate that when two objects are rubbed together, they become electrically charged.

The crucial question then arose: Where does this charge come from? The answer fundamentally changed our understanding of the atom: it is divisible and consists of charged particles.

Many brilliant scientists contributed to unraveling the mystery of these charged particles within the atom:

• The Electron: By 1900, it was well-established that the atom, previously thought to be indivisible, contained at least one sub-atomic particle – the electron. J.J. Thomson is credited with identifying the electron. Electrons are represented as 'e', have a negligible mass, and carry a charge of minus one.
• The Proton: Even before the electron was fully identified, E. Goldstein, in 1886, discovered the presence of new radiations in a gas discharge experiment, which he called canal rays. These rays were found to be positively charged. This discovery ultimately led to the identification of another sub-atomic particle: the proton. A proton is represented as 'p', its mass is taken as one unit, and it carries a charge of plus one. Significantly, the charge of a proton is equal in magnitude but opposite in sign to that of an electron. Its mass is approximately 2000 times that of an electron.

The discovery of electrons and protons suggested that an atom was composed of these two types of charged particles, with their charges mutually balancing each other, explaining why atoms are generally electrically neutral. It also became apparent that protons were likely located in the interior of the atom, as electrons could be easily removed, but not protons.

With the discovery of these fundamental particles, the next big question for scientists was: What sort of structure did these particles form within the atom? How were they arranged? This set the stage for the development of various atomic models, each attempting to explain the atom's internal architecture.

Question for You: If an atom contains one electron and one proton, will it carry any net charge or not? Explain your reasoning.