Structure of the atom
|Automatic translation||Updated November 06, 2013|
Everything we see is made up of atoms, many atoms. It was watching the smallest constituents of the matter that scientists have been able to explain, in the twentieth century, the operation of the entire universe. An atom is constituted by a core around which moves one or more electrons. What characterizes the core is its number of protons ( Z) ranging from 1 to 110, it is it who determines the element, such as iron (FE26) has 26 protons, 26 is the atomic number. The number of neutrons (N) ranging from 0 to 160, characteristic of the isotopes of the element, for example, hydrogen (H1) has a proton and no neutron, deuterium (H2) has a proton and a neutron, tritium (H3) has a proton and two neutrons. These three forms of hydrogen have only one electron, since there is only one electrical load, the single proton. Attention that it is only in the case of hydrogen that is given a different name to the isotopes of the element, in all other cases we indicate only the number of nucleons thereby find the number of neutrons. For example iron (FE26) has several isotopes Fe56, we understand that Fe56 has 30 neutrons, Fe57 has 31 neutrons, Fe58 32 neutrons, the number of neutrons differs well isotopes.
In 1911, Ernest Rutherford (1871-1937) discovered the atomic nucleus and specifies the structure of the atom by bombarding gold foil with particles from the radioactive decay of uranium. He gives a nucleus size in the order of 10-14 meters. There is a little more than one hundred different atoms, these are the elements such as hydrogen, carbon, oxygen or iron. The New Zealand physicist had the idea of a representation of the atomic nucleus. Rutherford represents each atom as a mini solar system, the center and the nucleus like planets orbit the electrons. The nucleus itself is represented as a mature grains (picture to the right). This pictorial representation is false but has two advantages, it clearly differentiates the two particles, the proton and neutron and we understand that the core, very compact, is circumscribed within a defined volume. But since the advent of quantum mechanics in the 1920s, the nucleus image is disturbing, the nucleus is no longer a system of balls associated together. The nucleus is governed by quantum mechanics, in other words it exist than if it is observable but observe the protons and neutrons inside the nucleus as they are in the picture, is not possible because it would illuminate the particles with a light so intense that the nucleus would instantly disintegrate. This representation in form of grains blackberry hides the quantum concept of matter. It is the same for the electron, no longer represents the electron as a particle which rotates on a very regular orbit around the nucleus. The electron is both a wave and a particle, the wave-particle duality is the foundation of quantum mechanics. In quantum mechanics the electron does not follow a single path, it is located in a region around the nucleus, called the electronic cloud or atomic orbital.
Image: Representation of the atomic nucleus, in the form of grains blackberry, has two advantages, we differentiate the two particles, the proton and neutron, and it is clear that the nucleus, very compact, is circumscribed within a defined volume. All nucleus and all isotopes have between 1 and 110 protons and between 0 and 160 neutrons. However, this representation is false because it hides the quantum concept. Since the 1920s, the nucleus is no longer a system of balls associated together, it is a quantum system much more troubling.
Electron cloud or atomic orbital
Since 1924, all matter is associated with a wave, is the assumption of Louis de Broglie (1892-1987). With this hypothese, he generalizes to all the particles of matter, wave-particle duality brought to light by Max Planck (1858-1947) in the early 20th century. All subatomic particles therefore have a wavelength.
If you no longer represents the electron as a point particle on a regular orbit around a nucleus, how can you make a picture?
Image: Representation of the first electronic orbitals of hydrogen based on the energy of the electron and its angular momentum, the energy level increases from top to bottom (n = 1 , 2, 3) and the momentum increases from left to right , (I = s , p, d , f , g) . This image shows the probability density of finding the electron, the black color represents the density 0, i.e. the area where the electron will never adventure. The white color represents the maximum density, i.e. the area where the electron passes most often. Between black and white in the orange-red zone, the probability density increases. Quantum numbers are represented by letters n, is the principal quantum number, it defines the energy level of the electron. I is the orbital quantum number, or secondary, as it defines the electronic sublayers, s (sharp) for l = 0 , p (principal) for l = 1 , d (diffuse) for l = 2 , f (Fundamental) for I = 3 , then (to the excited states ) g , h , i ,... the quantum number m is the magnetic quantum number or tertiary .