Why is oxygen almost always a molecule

Elements, school book

36 2 THE CHEMICAL BONDING Important molecules and their names The naming of molecules does not follow a strict system. Many molecular compounds have historically determined trivial names (everyday names) and systematic names are only used to a very limited extent. In the following, the most important molecules - sorted according to compound classes - are presented and their names are given. Elements For non-metals, the element name is identical to the name of the atom. If there is a risk of confusion, the term “molecule” or “atom” must follow the name. In most cases, however, one speaks of real substances in their real - ie. molecular - manifestation. Hydrogen, the non-metals of the 2nd period and the halogens (the exception “carbon” is dealt with in detail in Section 2.4) form diatomic molecules (H 2, O 2, N 2, F 2). A structural peculiarity that cannot be explained with the models discussed, however, occurs with oxygen. The expected structure - double bond between the oxygen atoms - does not agree with experimental data in all points. Each oxygen atom has an unpaired electron. Compounds with unpaired electrons are called radicals. Radicals are particularly reactive. Oxygen is called a biradical due to the two unpaired electrons. His responsiveness is easy to explain. From the 3rd period onwards, the formation of multiple bonds is avoided in the elementary state. Large groups of molecules are formed by single bonds. In the case of sulfur, 8 sulfur atoms combine to form a ring-shaped S 8 molecule. Phosphorus forms a tetrahedral P 4 molecule from 4 atoms. However, it has become common practice to use only the element symbol for phosphorus and sulfur (Fig. 36.1). Hydrogen compounds These almost always obey the octet rule. Therefore, creating these formulas is particularly easy. The naming is mostly done with trivial names (Fig. 36.2). Oxygen compounds This class of compounds is commonly referred to as oxides. If several oxides are possible for an element, the number of oxygen atoms is given with Greek prefixes - mono-, di-, tri- etc. -. With some oxides of nitrogen, radicals occur due to the odd total number of electrons (Fig. 36.3). Oxygen acids In addition to a non-metal and oxygen, these also contain one or more hydrogen atoms. The H atoms are almost always bound to the oxygen atoms. There are normally no bonds between oxygen atoms (Fig. 36.4). ■ 36.1: Find those molecules from Fig. 36.1 to 36.4 that are radicals! ■ 36.2: Hydrocyanic acid is a molecule made up of H, C and N atoms. Draw up a possible structural formula (H and N atoms bound to C atom)! EXERCISES elements H 2 hydrogen F 2 fluorine Cl 2 chlorine Br 2 bromine I 2 iodine O 2 oxygen S 8 (S) sulfur N 2 nitrogen P 4 (P) phosphorus hydrogen compounds HCl hydrogen chloride aqueous solution: hydrochloric acid H 2 O water NH 3 ammonia N 2 H 4 hydrazine H 2 S hydrogen sulfide PH 3 phosphane CH 4 methane SiH 4 silane oxides SO 2 sulfur dioxide SO 3 sulfur trioxide NO nitrogen monoxide NO 2 nitrogen dioxide N 2 O 4 nitrous tetroxide N 2 O nitrous oxide P 4 O 10 phosphorus (V) oxide CO carbon monoxide CO 2 carbon dioxide oxygen acids H 2 SO 3 sulphurous acid H 2 SO 4 sulfuric acid HNO 2 nitrous acid HNO 3 nitric acid H 3 PO 4 phosphoric acid H 2 CO 3 carbonic acid Fig. 36.1: Molecules of elements (formula and name) Fig. 36.2: Molecules of Hydrogen compounds (formula and name) Fig. 36.3: Molecules of oxides (formula and name) Fig. 36.4: Molecules of oxygen acids (formula and name) For testing purposes only - property of the publisher öbv

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