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What is an atom? Statement:

The word 'atom'goes back to the Greek philosopher Democritus and means' indivisible'. The idea of ​​the indivisibility of atoms, that is the smallest unit of matter, is thus well over 2,400 years old. However, atoms are not indivisible despite the terminology. Although chemistry is reaching its limits, with modern physical methods, such as nuclear fission, the division of atoms is possible today.
The ancient philosophers were already concerned with the question of what we humans, animals or plants really are, is a clear indication of the anthropological desire to understand the universe in its fundamentals. And that works best if you know the individual components that make up this universe. In the course of history wore u.a. John Dalton, Ernest Rutherford, Niels Bohr, Enrico Fermi and Albert Einstein contributed significantly to atomic research.
Put simply, atoms are the basic building blocks that make up everything that exists (so-called matter). For a long time it was not possible to observe atoms directly, so that their existence was assumed on a theoretical basis. Meanwhile, high-resolution electron microscopes are able to make even single atoms visible. This represents a huge step for the natural sciences, especially chemistry and physics.

Structure of an atom:

A bar of pure gold is made up of more identical atoms than humans live on earth. A bar of silver also consists of billions of identical atoms. So there must be a distinguishing feature or property of the atom that determines whether it is a gold atom or a silver atom. Before this question is resolved, the general structure of an atom follows first:
Each atom consists of one atomic nucleus and one atomic shell, The atomic nucleus contains about 99.9% of the atomic mass and consists of positively charged protons and neutrally charged neutrons. The atomic shell makes up the remaining 0.01% of the mass. It consists of negatively charged electrons. Since the number of protons in the atomic nucleus is identical to the number of electrons in the atomic shell, atoms are electrically neutral.
The number of protons in the atomic nucleus determines which chemical element ultimately belongs to a particular atom. In the periodic table of the elements, the number of protons can be easily read off by the ordinal number of the respective element. Ergo has 79 protons in gold and 47 in silver. As already mentioned, the number of protons corresponds to that of the electrons. The number of electrons is thus identical to that of the protons (gold with 79 electrons, silver with 47 electrons).

Schematic illustration of an atom:

Atomic models:

Democratic Particle Model
Dalton's atomic model
Thomson's atomic model
Rutherford's atomic model
Bohr's atomic model
shell model
orbital model