Metal hydroxide
Metal hydroxides are also known as strong bases. Many common metal hydroxides are made up from hydroxide ions and the ion of the particular metal that it is made up of. Example: When NaOH (sodium hydroxide) is dissolved in water, it forms OH ions and Na ions. Metal hydroxides ionize completely when dissolved, so that is why they are known as strong bases. Their pH is above 7, labeling them as bases. Since ions conduct electricity, metal hydroxides carry electricity very well when they are dissolved.In soils, it is assumed that larger amounts of natural phenols are released from decomposing plant litter rather than from throughfall in any natural plant community. Decomposition of dead plant material causes complex organic compounds to be slowly oxidized (lignin-like humus) or to break down into simpler forms (sugars and amino sugars, aliphatic and phenolic organic acids), which are further transformed into microbial biomass (microbial humus) or are reorganized, and further oxidized, into humic assemblages (fulvic and humic acids), which bind to clay minerals and metal hydroxides.
Hydroxide
The amphoteric hydroxide Al(OH) has four major crystalline forms: gibbsite (most stable), bayerite, nordstrandite, and doyleite.
All these polymorphs are built up of double layers of hydroxide ions – the aluminium atoms on two-thirds of the octahedral holes between the two layers – and differ only in the stacking sequence of the layers. The structures are similar to the brucite structure. However, whereas the brucite structure can be described as a close-packed structure in gibbsite the OH groups on the underside of one layer rest on the groups of the layer below. This arrangement led to the suggestion that there are directional bonds between OH groups in adjacent layers. This is an unusual form of hydrogen bonding since the two hydroxide ion involved would be expected to point away from each other. The hydrogen atoms have been located by neutron diffraction experiments on α-AlO(OH) (diaspore). The O–H–O distance is very short, at 265 pm; the hydrogen is not equidistant between the oxygen atoms and the short OH bond makes an angle of 12° with the O–O line. A similar type of hydrogen bond has been proposed for other amphoteric hydroxides, including Be(OH), Zn(OH), and Fe(OH).