We are now in a much more comfortable Situation
The chemist DMITRI MENDELEEV and LOTHAR MEYER had organized in, the then-known elements according to their atomic masses and the first periodic system of the elements (PSE)In particular, MENDELEEV realized that most of the properties of the elements in a similar way for heavier elements to be repeated several times - i.e, periodically-. Due to the similar characteristics, he placed the elements in groups of eight. The VIII group not included at that time the then unknown noble gases, but the present-day in addition to group elements (figure). MENDELEEV formulated the law of periodicity, which States that the properties of the elements periodic - periodic - in relation to the atomic weights or mass change. Using this law, he could say the as-yet-unknown elements of Gallium (ECA-aluminum), Germanium (ECA-silicon), and Scandium (ECA-boron) with their properties relatively accurately. The achievements of MENDELEYEV are all the more impressive as he had only simple measurement methods, without any knowledge about the internal structure of the atoms had. MENDELEEV and MEYER set up your PSE on the Basis of the diatonic atom model, that is, you just knew neither protons nor electrons. We know that the order in the PSE according to the atomic weight exactly, but according to the number of protons. The classification of elements into various periods and groups, in contrast, is by its electron configuration, i.e, due to the occupation of the electron shells. Hence, the Change in the properties of the elements within the periodic table can be explained. The beginning of a period according to the current state of knowledge, where the added electrons occupy a higher energy level, so an additional shell of Electrons is filled. As a result, the properties of the elements by leaps and bounds (for example, from Helium to Lithium or from Neon to sodium change).
Example: Lithium and potassium atoms have an outer electron
Within a period, the number of electrons in the atom takes cover while continuously to, however, the outer electrons in the same electron shell, i.e, in almost the same distance from the core.
The nuclear charge is increasing with each Element by one unit (a Proton).
Consequently, the attraction of the electrons increases due to the positively charged nucleus within a period. Accordingly, each of the properties of the elements within a period (figure). The example of the. Period shown the Trend is repeated in a similar manner also in the case of the main group elements of higher periods. Already MENDELEEV recognized the Similarity of certain elements and arranged in same groups. Today, we know that this Similarity is due to the fact that all the elements of a group have exactly the same number of outer electrons, or valence electrons. These valence electrons mainly determine the chemical properties, since they are involved in the formation of the chemical bonds. Also within the main groups can be observed recurring Trends in the Changes of properties. This periodicity, however, is different than the Change within the groups. The cause is primarily within the groups, although the nuclear charge increases, however, each heavier element atom contains an additional fully occupied electron shell. This additional shell shields the valence electrons from the charge of the nucleus, so the outer electrons are always bound to loose. The potassium atom gives its valence electron, however, despite the higher nuclear charge lighter than a lithium atom because the valence electron is shielded by the K - and L-shell from the core. The example of the V. main group, the General, in each main group recurring Trends in the properties observed (figure): the repetition of The General Trends in the periods and in the groups of the PSE it is referred to as the periodicity of the properties. All the elements strive to achieve by the release or absorption of electrons or by training the chemical bonds in an energetically stable state. Such States of the eight-shell of the neon, as well as the full electron configuration of the other noble gases. Metals are characterized in that the atoms have relatively few valence electrons, and the ionization energy is relatively low.
Because the electrons can easily be emitted, they form positively charged ions.
The number of charge corresponds to the case of main group elements the main group number. Metals are found in the periodic system in dependence of the number of its outer electrons to the left. The number of outer electrons of atoms of non-metals is relatively high. Accordingly, it is found in the PSE on the right. Electrons from the atom solve the case out, would be a significant ionization energy needed. Therefore, they form negatively charged ions, by electrons are added. Non-metals are also recognized by the fact that they form oxides, which react in water is acidic. In the period of system you are on the right side, and in particular for the lighter elements. Between the metals and non-metals to the metals. These elements III. main group, hardly any, but such as boron and silicon atoms shared pairs of electrons with other atoms. The oxides of semi-metals can react with both acidic as well as alkaline. The value of is an important chemical property of elements, which is, however, difficult to comprehend.
You will not incorrectly set the oxidation number or ionic charge is equal, what is true, however, in all cases.
The value specifies how many fluorine and hydrogen atoms are bound to an Atom or Ion of an element theoretically, or can replace it. The value is mainly determined by the valence electron configuration of the elements, and also as a valence.
With each valence electron can form an Atom, theoretically an electron pair to another Atom.
Alternatively, the noble gas configuration in the Compounds can also be achieved by the formation of ions. To neutralize the ionic charge must be tied to a corresponding number of oppositely charged ions. The number of binding partners is thus determined by the number of outer electrons of an Atom. Of the I. main group, the number of outer electrons increases continuously from one to eight.
This process is repeated, within each period, so that the maximum value corresponds to the number of the main group of the element (figure).
This rule applies to the maximum valency towards oxygen, and fluorine with one caveat. The elements of the. Period have only orbitals on four-Atom and can form, therefore, a maximum of four bonds. The valency of main group elements with respect to hydrogen increases up to the IV. The main group, and then decreases again, i.e, one observes a so-called"roof effect"(figure).
