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Although most metal oxides are crystalline solids, many non-metal oxides are molecules. Examples of molecular oxides are carbon dioxide and carbon monoxide. All simple oxides of nitrogen are molecular, e.g., NO, N 2 O, NO 2 and N 2 O 4. Phosphorus pentoxide is a more complex molecular oxide with a deceptive name, the real formula being P 4 O 10.
Crystal structure of rubidium oxide. Lithium oxide (Li 2 O) is the lightest alkali metal oxide and a white solid. It melts at 1570 °C. Sodium oxide (Na 2 O) is a white solid that melts at 1132 °C and decomposes at 1950 °C. It is a component of glass. Potassium oxide (K 2 O) is a pale yellow solid that decomposes at 350 °C.
For example, the basic oxide Li 2 O becomes the hydroxide LiOH, and BaO becomes Ba(OH) 2 after reacting with water. In contrast, non-metals usually form acidic oxides . In general, the basicity of oxides increases when towards the lower-left corner of the periodic table , which corresponds to increased metallic properties.
Transition metal oxides are compounds composed of oxygen atoms bound to transition metals. They are commonly utilized for their catalytic activity and semiconducting properties. Transition metal oxides are also frequently used as pigments in paints and plastics , most notably titanium dioxide .
Metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Many metals (such as zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides. Aluminium oxide (Al 2 O 3) is an example of an amphoteric oxide. Amphoterism depends on the oxidation states of the oxide.
Carbonic acid is an illustrative example of the Lewis acidity of an acidic oxide. CO 2 + 2OH − ⇌ HCO 3 − + OH − ⇌ CO 3 2− + H 2 O. This property is a key reason for keeping alkali chemicals well sealed from the atmosphere, as long-term exposure to carbon dioxide in the air can degrade the material.
Typical examples are ilmenite (FeTiO 3), a mixed oxide of iron (Fe 2+) and titanium (Ti 4+) cations, perovskite and garnet.The cations may be the same element in different ionization states: a notable example is magnetite Fe 3 O 4, which is also known as ferrosoferric oxide , contains the cations Fe 2+ ("ferrous" iron) and Fe 3+ ("ferric" iron ...
The oxides of elemental metals are often basic. However, oxides with very high oxidation states such as CrO 3, Mn 2 O 7, and OsO 4 often have strictly acidic reactions; and oxides of the less electropositive metals such as BeO, Al 2 O 3, and PbO, can display both basic and acidic properties.