Atoms are the basic building blocks of matter that make up everyday objects. There are 90 naturally occurring kinds of atoms.
An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive charge or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protonsdetermines the chemical element, and the number of neutrons determines the isotope of the element.
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History of (Topic)
The name atom come from the Greek "atomos", which means uncuttable or invisible, something that cannot be devided.
Around 460 B.C., did a Greek philosopher, Democritus, develop the idea of atoms. He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms.

Application of (Topic)

The centre-of-mass position and momentum of an (N + 1)-particle system are treated as superselection rules. As a consequence, particle positions and momenta do not obey Heisenberg commutation rules. A Schrödinger equation for the internal state is obtained in terms of the (N + 1)-particle original positions. Application to atoms justifies the fixed-nucleus approximation as consistent with the classical CM premises. Application to nuclear structure gives at once the Schrödinger equation for the intrinsic states. The present theory allows system states to be altogether localized, translation invariant with respect to a laboratory frame, and with a nonzero total momentum.


  1. Beiser, A. (1988). Physical Science (2nd Edition). New York, NY: McGraw Hill

  3. From Atoms to Quarks: An Introduction to the Strange World of Particles by, James Terell

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