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Left: The dot-and-cross diagram of the LDQ structure of ozone (O 3). The nuclei are as indicated and the electrons are denoted by either dots or crosses, depending on their relative spins. Right: Simplified diagram of the LDQ structure of O 3, showing electrons in non-coincident pairs using thin lines and a coincident electron pair using a ...
[1] [2] [3] Introduced by Gilbert N. Lewis in his 1916 article The Atom and the Molecule, a Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. [4] Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.
The AKF diagram is intended for rocks containing excess aluminium and silica. Its components are: A = Al 2 O 3 - (CaO + Na 2 O + K 2 O) K = K 2 O F = FeO + MgO + MnO. This diagram is less useful, because magnesium does not freely substitute for ferrous iron in many metamorphic minerals important in aluminium-rich rock.
While "magnesium oxide" normally refers to MgO, the compound magnesium peroxide MgO 2 is also known. According to evolutionary crystal structure prediction, [11] MgO 2 is thermodynamically stable at pressures above 116 GPa (gigapascals), and a semiconducting suboxide Mg 3 O 2 is thermodynamically stable above 500 GPa. Because of its stability ...
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The structure of phase 5 is believed to be similar, with generic formula [(Mg 3 (OH) 5 (H 2 O) x) n] n+ (Cl −) n (H 2 O) n(4−x). [ 17 ] The anhydrous forms of phase 3 and phase 5 have the same structure as Mg(OH) 2 : namely, layers of magnesium cations, each sandwiched between two layers of hydroxy or chloride anions.
In the solid state, MgO 2 has a cubic pyrite-type crystal structure with 6-coordinate Mg 2+ ions and O 2 2− peroxide-groups, according to experimental data [2] and evolutionary crystal structure prediction, [3] the latter predicting a phase transition at the pressure of 53 GPa to a tetragonal structure with 8-coordinate Mg 2+ ions.
Using equation 5, the formula can be simplified into the following form where the enthalpy of formation can be directly calculated: [v ′ ′ {\displaystyle \prime \prime } Mg ] = exp ( − Δ f H / 2 k B T + Δ f S / 2 k B ) = A exp ( − Δ f H / 2 k B T ) , where A is a constant containing the entropic term.