| Picture Viewer |
Whatever - Science 101 (and sometimes 201) 
MSFixR says: The Atom The atom is one of the most fundamental particles in ordinary matter. A chemical element is determined entirely by the type of atom it contains, which in turn is determined by the number of protons, electrons and neutrons that constitute the atom. An atom consists of a dense nucleus, consisting of positively charged protons and electrically neutral neutrons, bound together by the strong nuclear force. Surrounding the nucleus at a distance some 10 000 times the nuclear diameter, are the negatively charged electrons, constrained by their electrostatic attraction to the nucleus. When the number of protons in the nucleus equals the number of electrons, the atom is electrically neutral; otherwise it is an ion and has a net positive or negative charge. An atom is classified according to its number of protons and neutrons: the number of protons determines the chemical element and the number of neutrons determines the isotope of that element. An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) is in reality spherically symmetric, although for more complicated nuclei this is not always the case. The black bar is one ångström, equal to 0.0000000001 meters or 100,000 fm.
The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and the early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was not indivisible. The principles of quantum mechanics were used to successfully model the atom. Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses that can only be observed individually using special instruments such as the scanning tunneling microscope. More than 99.9% of an atom's mass is concentrated in the nucleus, with protons and neutrons having about equal mass. In atoms with too many or too few neutrons relative to the number of protons, the nucleus is unstable and subject to radioactive decay. The electrons surrounding the nucleus occupy a set of stable energy levels, or orbitals, and they can transition between these states by the absorption or emission of photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties To learn more, see Wikipedia Original post: Science 101 (and sometimes 201) |
All times are GMT -4. The time now is 06:43 AM.
