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Ball-and-stick model of superconductor magnesium diboride. Boron atoms lie in hexagonal aromatic graphite-like layers, with a charge of −1 on each boron atom. Magnesium(II) ions lie between layers. Binary metal-boron compounds, the metal borides, contain only boron and a metal. They are metallic, very hard, with high melting points.
Each boron atom has a formal −1 charge and magnesium is assigned a formal charge of +2. In this material, the boron centers are trigonal planar with an extra double bond for each boron, forming sheets akin to the carbon in graphite. However, unlike hexagonal boron nitride, which lacks electrons in the plane of the covalent atoms, the ...
Various representations of bonding in borenium ions. [2]A borenium ion is an inorganic cation with the chemical formula [BR 2 L] +In this class of molecules, the electron-deficient boron center has two valence electrons involved in sigma bonding with two ligands, while the third ligand is a two-electron donor such that the overall charge of the complex is +1. [1]
Polymeric boron oxoanions are formed in aqueous solution of boric acid at pH 7–10 if the boron concentration is higher than about 0.025 mol/L. The best known of these is the tetraborate ion [B 4 O 7] 2−, found in the mineral borax: 4 [B(OH) 4] − + 2 H + ⇌ [B 4 O 5 (OH) 4] 2− + 7 H 2 O
The reduced noble gas binding strength can be attributed to a less electrophilic vacant boron atom in the case of X = F, because the atomic charge of the vacant boron calculated using the Natural Population Analysis (NPA) method is + 0.45 e, while it is much larger for the other halogens (for X = Cl, for example, + 0.64 e).
As an example, summing bond orders in the ammonium cation yields −4 at the nitrogen of formal charge +1, with the two numbers adding to the oxidation state of −3: The sum of oxidation states in the ion equals its charge (as it equals zero for a neutral molecule). Also in anions, the formal (ionic) charges have to be considered when nonzero.
Boric acid in equilibrium with its conjugate base the borate ion is widely used (in the concentration range 50–100 ppm boron equivalents) as a primary or adjunct pH buffer system in swimming pools. Boric acid is a weak acid, with p K a (the pH at which buffering is strongest because the free acid and borate ion are in equal concentrations) of ...
The reasons for the existence of diagonal relationships are not fully understood, but charge density is a factor. For example, Li + is a small cation with a +1 charge and Mg 2+ is somewhat larger with a +2 charge, so the ionic potential of each of the two ions is roughly the same.