The following article describes the structure of the atom and how it opened as a theory developed in their minds and in experiments thinkers and scientists.The quantum-mechanical model of the atom as the most advanced by far the most fully describes its behavior, and the particles that make up.About it and its features, see below.
concept of atom
Chemically minimum indivisible part of the chemical element with a set of specific properties is for him an atom.It includes electrons and the nucleus, which in turn contains a positively charged protons and neutrons are uncharged.If it contains the same number of protons and electrons, the atom itself is electrically neutral.Otherwise he has a charge: positive or negative.Then the atom is called an ion.Thus the classification is carried out: a chemical element is determined by the number of protons, and its isotope - neutrons.Communicating with each other on the basis of the interatomic bonds, atoms form the molecule.
first started talking about atoms ancient Indian and Greek philosophers.And during the seventeenth and eighteenth centuries chemists have confirmed the idea experimentally proved that some substances can not be split into their constituent elements by chemical experiments.However, from the late nineteenth to the early twentieth centuries, physicists discovered subatomic particles, so that it became clear that the atom is not indivisible.In 1860, chemists have formulated the concept of atoms and molecules, where the atom was the smallest particle of an element that was part of both simple and complex substances.
models of atomic structure
- pieces of matter.Democritus believed that the properties of substances can be defined mass, shape, and other parameters that characterize the atoms.For example, the fire has sharp atoms, because of which has the ability to burn;solids contain rough particles, thereby engage with each other is very strong;in water, they are smooth, so it is able to flow.According to Democritus, even the human soul is composed of atoms.
- Thomson model.The scientist considered the atom as a positively charged body, inside of which are electrons.These models are denied Rutherford spent his famous experience.
- Early planetary model of Nagaoka.In the early twentieth century Hantaro Nagaoka suggested model of the nucleus of the atom, like the planet Saturn.They are around a small nucleus, positively charged, spun together in a ring of electrons.These versions are the same as the previous ones, it was wrong.
- Planetary Rutherford-Bohr model.After several experiments, Ernest Rutherford proposed that an atom is like a planetary system.In it the electrons move in orbits around the nucleus, which is positively charged and is in the center.But contrary to the classical electrodynamics, since, according to her, the electron, moving, emits electromagnetic waves and therefore loses energy.Bohr introduced special postulates on which the electrons do not emit energy, while being in some specific conditions.It turned out that classical mechanics was unable to describe the models of atomic structure.This further led to the emergence of quantum mechanics allows us to explain how this phenomenon, and many others.
Quantum-mechanical model of the atom
This model is an evolution of the previous one.The quantum-mechanical model of the atom suggests that the nucleus of the atom are not charged with neutrons and positively charged protons.It is surrounded by negatively charged electrons.But in quantum mechanics, the electrons do not move in a predetermined specific traektoriyam.Tak, in 1927 announced Heisenberg uncertainty principle, which is impossible for a precise definition of the coordinates of the particle and its velocity or momentum.
chemical properties of electrons determine their shell.In the periodic table atoms are arranged according to the electric charge of the nuclei (it is the number of protons), neutrons, while not affect the chemical properties.The quantum-mechanical model of the atom has proved that its main weight falls on the core, and the share of electrons, however, remains low.It is measured in atomic mass units, which is equal to 1/12 of the mass of an atom of carbon isotope C12.
orbital wave function and
Geyzentberga V. According to the principle, we can not say with absolute certainty that the electron, which has a certain speed, is in a particular point in space.In order to describe the properties of the electron wave function Psi use.
probability of finding a particle at a particular time is directly proportional to the square of its absolute value, which is calculated for a specific time.Psi in the square called the probability density that characterizes the electrons around the nucleus in the form of the electron cloud.The longer it is, the probability of an electron in a certain space of the atom will be higher.
For a better understanding can be represented pictures superimposed on one another, where the fixed position of the electron at different times.In the place where the points will be greater and the cloud become the most dense, and the highest probability of finding the electron.
calculated, for example, that the quantum-mechanical model of the hydrogen atom includes the highest density of the electron cloud at a distance of 0,053 nm from the nucleus.
orbit of classical mechanics is replaced by quantum electron cloud.The wave function of an electron is called the orbital psi, which is characterized by the shape and energy of the electron cloud in space.With regard to an atom refers to the space around the core, wherein the presence of the electron is the most probable.
impossible - possible?
Like all theory, quantum-mechanical model of atomic structure is truly made a revolution in the scientific world and among the inhabitants.Indeed, to this day it is difficult to imagine that one and the same particle at the same time can not simultaneously be in one, but in different places!To protect the well-established ways of life say that in the microcosm there are events that are impossible and are not those in the macrocosm.But is it really?Or people are just afraid to admit even the possibility that "a drop is like an ocean and ocean - drop"?