What is a non-metal
The non-metals form a group of chemical elements which, in contrast to the metallic elements, lack the characteristic properties of a metal, since they are poor conductors of heat and electricity, have relatively low densities, melting and boiling points, and have high values for ionization energy, electron affinity and, among other things Have electronegativity, are non-shiny, gaseous, non-metallic, brittle or liquid and not malleable in terms of material.
In detail, all 17 non-metals belong to the main group elements, namely the noble gases (helium, argon, neon, krypton, xenon, radon - oganesson uncertain), the halogens fluorine, chlorine, bromine, iodine, as well as oxygen, sulfur, selenium , Nitrogen, phosphorus, carbon and hydrogen.
The non-metals are divided into two categories, which reflect their - under "normal" conditions - their relative tendency to form chemical compounds: namely reactive non-metals and noble gases. The reactive non-metals vary in their non-metallic character. The less electronegative substances, such as carbon and sulfur, usually have weak to moderately strong non-metallic properties and tend to form covalent bonds with metals. The more electronegative reactive non-metals such as oxygen and the halogens are characterized by stronger non-metallic properties and a tendency to form predominantly ionic compounds with metals. The noble gases, on the other hand, show a great reluctance to enter into bonds with other elements or to form noble gas compounds.
However, the assignment of an element to the group of non-metals or to a sub-group is not to be regarded as absolute. In particular, under certain conditions there are modifications of one of the elements mentioned which show more or less metallic properties. Examples are carbon - in the form of the non-metallic diamond and the semi-metal graphite - or hydrogen in its metal-like high-pressure modification.
In addition, there is no generally accepted definition of a non-metal: elements in places in the periodic table where the metals meet the non-metals are classified inconsistently by various textbook authors. Elements that are sometimes classified as non-metals are the metalloids boron, silicon, germanium, arsenic, antimony, tellurium and astatine. The non-metal selenium is sometimes classified as a metalloid, especially in environmental chemistry.
Properties of the non-metals
Non-metals show a greater diversity in their properties than metals. These properties are largely determined by the interatomic bond strengths and molecular structures, both of which vary as the number of valence electrons in each nonmetal varies. In contrast, metals have a more homogeneous structure and their properties can be more easily reconciled with one another.
Physically, the non-metals exist mostly as di- or monatomic gases under normal conditions, with the rest - in contrast to the metals, whose atoms are almost all tightly and densely packed - have an open-packed atomic arrangement. With the exception of sulfur, the solids have a submetallic appearance and, in contrast to the metals, which are shiny and generally ductile or malleable, are mostly brittle. In addition, they usually have lower densities, are inferior conductors for heat and electricity and tend to have much lower melting points and boiling points than those of metals.
Chemically, the non-metals usually have high ionization energies, high electron affinities (nitrogen and the noble gases negative electron affinities) and high electronegativity values. and in general they form ionic or covalent bonds with metals and have acidic oxides, while the common oxides of almost all metals are basic.
Category: Chemical elements.
Updated on 06.05.2020.
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