Atoms are infinitesimal units that form matter. The term is derived from Greek word atomos, which means indivisible.They are everywhere combining with each other to form more complex molecules. Atoms are the material that form the elements. When two or multiple atoms conjoin this creates a compound. Seeing as the universe is immense the number of atoms is also enormous. The actual size of the atom is estimated to be one angstrom in total diameter. That is one-ten-billionth meter. Understanding matter at a ultramicroscopic level is the goal of particle physics. Existence is physical matter at large scales and small scales.
The atom contains a certain structure. The internal structure of the atom contains a nucleus. The nucleus is constructed by two different particles. The neutrons and protons are the foundation of the nucleus. The proton has a positive charge and the neutron has no charge at all. Electrons have a negative charge and are concentrated in orbitals outside the nucleus. The electrons do give a particular material its chemical and physical properties. Neutrons, protons, and electrons are classified as elementary particles. Normally, these particles are referred to as subatomic. Elementary particles are made of quarks. These strange particles merge to make charges that are equal to zero or whole number multiples of an electron charge. They come in six varieties which include strange, top, up,bottom, charm, and down quarks. There could be more particles that have not been detected. The standard model will one day be expanded when physicists explore the full dynamics of string theory. Since ancient history there has been a theory of atoms. Due to the lack of technology and experimental limitations it could not be confirmed. With the rise of chemistry and physics evidence became available. Ernest Rutherford a physicist from New Zealand discovered that atoms have a nucleus by means of a particle beam experiment (1911).He noticed peculiar behavior of alpha particles.
The modern day model of the stricture of the atom .
A sheet of metal was placed in front of the particle detector. Rutherford noticed particles were being deflected. He deduced that there was a positively charged nucleus in the atoms of the metal which caused the repulsion. Scientist had developed numerous models of atomic structure. Prior to Ernest Rutherford's model there was the Dalton model. John Dalton believed that the atom was just one single particle with no extra structure. John Joseph Thompson confirmed the existence of the electron in 1897. the model was revised again, this time being replaced with the plum pudding model. Rutherford's discovery discredited that view of atomic structure. Niels Bohr felt the Rutherford model was not accurate and proposed the planetary model. The particles of the atom functioned like the Solar System in terms of motion. The nucleus was like the Sun using it gravitation to hold electrons in place. Bohr a Danish physicist, proposed this in 1913 before the rise of quantum mechanics.
Atomic models through the century.
By the 1950s quantum mechanics explained the kinematic nature of particles. This required another update. The modern day model displays a nucleus with neutrons and protons. Electrons still occupy orbitals, but are in an electron cloud. The orbital model is influenced by the Heisenberg uncertainty principle. According to that theory, it is impossible to know the position and velocity of any given electron in the orbital cloud. They can be located by probability clouds and be approximated. If the cloud happens to be dense, then it seems more likely to determine the position of the electrons. While precision is preferable, this provides the best explanation for atomic structure. Since 1803, when John Dalton proposed the indivisible model of the atom there have been significant advances. Humanity now the understanding of nuclear fusion and fission. As particle accelerators become more powerful humankind will be able to see what was thought to be invisible.
Further Reading
Binder, Julee. Ultimate Visual Dictionary. London: DK Publishing, 1994.
Barnes-Svarney, Patricia. Science Desk Reference. New York: Macmillan Company,1995.
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