He gathers the theoretical fundamental elements to be able to understand the scientific contemporary panorama.

...

A meteoroid is a smaller body whose size is between 100 mm and 50 m, this definition may vary but is used by the Royal Astronomical Society. Meteoroids like the interplanetary dust, come from the waste of the formation of the Solar System, from the collisions of bodies, and from ejections of comets. Usually they are chondrite (rocky), achondrite (similar to igneous rocks) or metallic. These move in orbits around the sun, and as has been said mostly come from comet ejections or collisions of celestial bodies. These have been concentrated in the plane of the ecliptic, decreasing their number as we approach the Sun and as we approach Jupiter, as both stars gravitationally capture most of the meteoroids. Meteoroids associated with comets or asteroids become meteors when they intercept Earth.

A meteor is the luminous phenomenon that occurs when the meteoroid crashes against the terrestrial atmosphere and by friction with this one becomes incandescent, popularly they are called shooting stars.

This interaction occurs in the thermosphere at a height between 80 and 120km, the speed of entry varies from 11 km / s for the slowest meteors to 80km / s for the fastest. The atmospheric particles hit the surface of the meteoroid by increasing its temperature, this process increases as the height decreases, when the meteoroid reaches a certain temperature the ablation process begins. In other words, the heat produced by the friction is enough to sublimate the atoms and molecules of the meteoroid. At this stage mass loss is rapid, this mass loss occurs in several ways, the most important being the separation of individual atoms and molecules from the

Chapter6

The periodic table of the elements is an arrangement of the chemical elements in the form of a table, ordered by their atomic number (number of protons), by their configuration of electrons and their chemical properties. This ordering shows periodic trends, as elements with similar behavior in the same column.

In the words of Theodor Benfey, the table and the periodic law "are the heart of chemistry-comparable to the theory of evolution in biology (which followed the concept of the Great Chain of Being), and the laws of thermodynamics in Classical physics. "

The rows in the table are called periods and the groups columns. Some groups have names. Thus, for example, group 17 is that of halogens and group 18 is that of noble gases. The table is also divided into four blocks with some similar chemical properties. Because the positions are ordered, the table can be used to obtain relationships between the properties of the elements, or to predict properties of new elements not yet discovered or synthesized. The periodic table provides a useful framework for analyzing chemical behavior and is widely used in chemistry and other sciences.

The atomic weights

At the beginning of the nineteenth century, John Dalton (1766-1844) developed a new conception of atomism, which was brought about by his meteorological studies and the gases of the atmosphere. Its main contribution consisted in the formulation of a "chemical atomism" that allowed to integrate the new definition of element realized by Antoine Lavoisier (1743-1794) and the ponderal laws of the chemistry (defined proportions, multiple proportions, reciprocal proportions).

Dalton used the knowledge of proportions in which the substances of his time reacted and made some assumptions about how the atoms of the same were combined. He established as a unit of reference the mass of a hydrogen atom (although others were suggested in those years) and referred the rest of the values ​​to this unit, reason why it was able to construct a system of relative atomic masses. For example, in the case of oxygen, Dalton started from the assumption that water was a binary compound, consisting of a hydrogen atom and an oxygen atom. He had no way of checking this point, so he had to accept this possibility as an a priori hypothesis.

Dalton knew that a part of hydrogen was combined with seven parts (eight, we would say at present) of oxygen to produce water. Therefore, if the combination were produced atom to atom, that is to say, a hydrogen atom was combined with an oxygen atom, the ratio of the masses of these atoms to be 1: 7 (or 1: 8 would be calculated in present). The result was the first table of relative atomic masses (or atomic weights, as Dalton called them), which was later modified and developed in later years. The inaccuracies mentioned above gave rise to a whole series of controversies and disparities with respect to the formulas and the atomic weights, that would only begin to surpass, although not totally, in the congress of Karlsruhe in 1860.

Periodic table of Mendeleyev

In 1869, Russian chemistry professor Dmitri Ivanovich Mendeleyev published his first Periodic Table in Germany. A year later, Julius Lothar Meyer27 published an enlarged version of the table he had created in 1864, based on the periodicity of atomic volumes as a function of the atomic mass of the elements.

By this date 63 elements of the 90 that already exist in nature were already known. Both chemists placed the elements in ascending order of their atomic masses, grouped them into rows or periods of different length and placed in the same group elements that had similar chemical properties, such as valence. They constructed their tables by listing the elements in rows or columns according to their atomic weight and beginning a new row or column when the characteristics of the elements began to recur.

In 1871, Mendeleyev published his periodic table in a new form, with groups of similar elements arranged in columns instead of rows, numbered I to VIII in correlation with the oxidation state of the element. He also made detailed predictions of the properties of the elements he had already pointed out that they were missing, but they should exist. These gaps were later filled when the chemists discovered additional natural elements

In its new table indicates the criterion of ordering of the columns are based on the hydrides and oxides that can form those elements and therefore, implicitly, the valences of those elements. It was still giving contradictory results (Silver and Gold appear duplicates, and there is no separation between Beryllium and Magnesium with Boron and Aluminum), but it was a breakthrough. This table was completed with one more group, made up of gas

Radiation is a detachment of energy generated by what is known as the radioactive decay of the unstable atomic nuclei of some chemical elements.

The