Why are non-metals naturally sproede
They are non-metals electronegative Elements that in the periodic table top right stand. They are typical anion formers. The following can be mentioned first:
- The elements are gases (noble gases, hydrogen, fluorine, chlorine, oxygen, nitrogen), liquids (bromine) or solids without metallic luster (sulfur, white phosphorus), which are mostly transparent.
- The solid elements are poor electrical conductors (exception: graphite).
- and mostly also bad heat conductors (exception: diamond).
- The semiconductors such as silicon, bismuth, selenium and tellurium form the transition to the metals (see below). Their band gaps are small and the elements are black or already have a metallic sheen (see Fig. 1.1.1.).
- metallic appearance, i.e. metallic luster of the surface
- ductile, ductile
- good thermal conductivity
- good electronic conductivity σ, i.e. low electrical resistance ρ
|1st Class||Metals||Cu||1.7 * 10-8||no|
|Li||8.6 * 10-8||no|
|Semi-metals||As||3.5 * 10-7||0|
|Bi||1.2 * 10-6||0|
|C (graphite)||0.8 * 10-5||0|
|2nd Class||semiconductor||Te||2 * 10-3||0.33|
|Si||1 * 101||1.17|
|Non-metals||Glass||109||>> 3 eV|
|S.||1014||>> 3 eV|
|C (diamond)||5.4 eV|
For the exact classification and the separation of the non-metals from the metals from a physical point of view, the σ is decisive. A distinction is then made between:
- 1st class leader (e.g. metals or semi-metals), in which an increase in temperature leads to a decrease in conductivity, i.e. to an increase in electrical resistance.
- Head of 2nd class (e.g. insulators or semiconductors), in which exactly the opposite effects occur. The conductivity increases with the temperature and the resistance decreases accordingly.
|Fig. 1.1.2. Temperature dependence of the electrical resistance ρ‣SVG|
- In the case of first class conductors (i.e. metals and semimetals), the number of charge carriers remains the same and high, but when the temperature rises, the atomic cores move more and the resistance increases. The decisive factor here is the decrease in the mobility of the charge carriers with increasing temperature.
- In the case of non-metals and semiconductors, i.e. in the case of 2nd class conductors, on the other hand, more electrons are only released from the atomic cores at higher temperatures, i.e. the number of charge carriers increases with increasing temperature.
The grouping into metals and non-metals is of course directly related to these physical measurements. The decisive factor is the energetic distance between occupied and unoccupied electronic states, in the MO model of molecular chemistry the HOMO-LUMO distance. Molecular compounds (without extensive interactions between the atomic orbitals) are therefore non-metals. In all solids, regardless of the type of bond, there is an interaction of a large number of atomic orbitals with one another, which leads to a broadening of the energy levels. In the extreme case (see Fig. 1.1.3. Right), this creates a continuous range of permitted electronic states (limit case electrons in a potential-free box), a simple model for a metal.
|Fig. 1.1.3. Description of the bond in solids (right: metal, see electron in the box) ‣SVG|
Based on the density of states (DOS = density of states, see Fig. 1.1.4.), The solids can then be divided into:
|Fig. 1.1.4. State views in metals, semi-metals, semiconductors and insulators‣SVG|
- Metals: overlapping (e.g. Ca) or partially occupied (e.g. Na) bands.
- Semimetals: valence and conduction bands just touching each other (no band gap, but only very low DOS at the Fermi level).
- Semiconductor: narrow (approx. 1-2 eV) forbidden zone between valence and conduction band
- Isolators: large forbidden zone between occupied valence and empty conduction band
As for the electronic properties (electronic conductivity) only the high-energy electrons in the uppermost area of the valence band are responsible, the above-mentioned electronic conductivity follows from this:
- Head of 1st class:
- & # 916 E = 0, DOSE.F. large -> metals
- & # 916 E = 0 / very small (guide value: kT = 0.03 eV = 30 kJ / mol), DOSE.F. = 0 / very small -> semi-metals
- Head of 2nd class:
- & # 916 E = 1 - 3 eV -> semiconductor
- & # 916 E> 3 eV -> non-conductors (insulators)
For the optical properties ('Absorption color') follows from the energy range of visible light (1.5 - 3.0 eV) that all solids with band gaps smaller than 1.5 eV appear black (or shiny metallic in the case of very small band gaps). Substances with wide conduction bands and band gaps between 1.5 and 3.0 eV are colored, with colors between yellow - orange - red - violet-brown - black (cf. metal sulfides).
The one between metals and non-metals cannot be clearly drawn either. A number of elements additionally form several modifications with different electrical properties and electronic structures:
|Fig. 1.1.5. Details on the boundary between metals and non-metals in the periodic table‣SVG|
- The elements of the subgroups are marked in light pink, the elements of the main group (p-block) in light red. All elements on the left of the section shown are real metals, all elements on the right are real non-metals!
- The line drawn in green indicates a limit according to the appearance of the elements. The classification becomes critical e.g. for carbon (graphite and diamond as polymorphs) or for Bi (extremely small band gap).
- Occasionally, a further distinction is also made:
- Semi-metals (marked here by yellow circles) are brittle and expand when heated. They have predominantly covalent structures (the 8-N rule for the bond is fulfilled), but already look metallic. They have no or only a tiny band gap, the density of states at the Fermi level is 0.
- 'Meta' metals (here marked by blue hexagons) form the transition links between metals and semi-metals. These elements have special structures, mostly derived from real metal packings through distortion. Physically they are real metals (1st class ladder).
- Aluminum and lead are real metals in the middle of the transition area!
- As a 'chemical' separation between metals (i.e. cation formers) and non-metals (i.e. anion formers) the so-called 'Zintl line' (shown above as a blue line between main group III and IV) can be seen. However, this limit does not apply strictly either, as the compound NaTl found by Zintl himself shows, in which a diamond-analogous Tl--Anion bond is present.
- As a limit for the lectures Chemistry of metals and Chemistry of non-metals becomes somewhat arbitrary the one in Fig. 1.1.6. line drawn in green is used:
|Fig. 1.1.6. Non-metals on the periodic table‣SVG|
|Fig. 1.1.7. Trends of various element properties in the periodic table‣SVG|
- The ion radii (for ions with a noble gas shell) are large,
- the atomic radii / distances in the element are small.All radii increase with the ordinal number in a group. Multiple bonds significantly affect the gears within a period.
- The electron affinity of the non-metals is negative (!), So the formation of anions is favored. The electron affinity falls in the PSE from left to right and increases from top to bottom. It is less negative for the alkaline earth metals (filled s subshell) and for the elements of the nitrogen group (half occupied p subshell).
- The 1st ionization energy of the non-metals is high (positive!), So the formation of cations is very unlikely. The ionization energy increases from bottom to top and from left to right in the periodic table.
- Non-metals have large electronegativities. Since the electronegativity is defined by the sum of IE and EA and the absolute values of the 1st ionization energy are significantly greater than those of the electron affinity, the electronegativity in the periodic table runs parallel to the 1st ionization energy.
- The oxygen compounds of the non-metals react acidic, so they are the anhydrides of strong acids.
the non-metallic elements are discussed essentially from right to left, namely
- Hydrogen, and its special position in the periodic table.
- The chemistry of all elements from the groups of noble gases, halogens and chalcogens.
- The first three elements of the penteles, nitrogen, phosphorus and arsenic (Sb and Bi are contained in the metals).
- From the group of tetreles only carbon and silicon (not Ge, Sn and Pb) are discussed.
- Boron is the only element of III. (13.) Group treated.
- technically important processes for the production of important raw materials
- as well as detailed excursions on concepts of chemical bonding in non-metal compounds at suitable points.
Specifically results for the lecture Chemistry of non-metals the following :
- Introduction, general
- Hydrogen (H)
- Noble gases (8th main group: He, Ne, Ar, Kr, Xe, Rn)
- Halogens (7th main group: F, Cl, Br, I, At)
- Chalcogens (6th main group: O, S, Se, Te, Po)
- Pentele (pnicogens, 5th main group, nitrogen group: N, P, As)
- Tetrele (4th main group: C, Si)
- Boron (triele, 3rd main group)
- 1.2 Chemical bond in non-metals and their compounds
- 1.3 Literature information
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