silicon iodide is an inorganic compound with the formula SiI4. It forms when silicon reacts with iodine vapour at 130 – 150 degC. It is colourless at room temperature. It is a precursor to silicon amides, which are used in the manufacture and etching of microelectronics. It is also a useful reducing agent in organic synthesis. It is highly sensitive to moisture and air and must be kept in a dry place. It is incompatible with magnesium, zinc and ammonia.
The chemical form of silicon that most people are familiar with is silica, which has the empirical formula SiO2. It forms in nature as quartz, sand and flint. The Earth’s crust is about 59 percent silica. It is found in water, plants, animals and even the human body, as in bone.
Like carbon, silicon can make diamond-like crystals. But unlike carbon, it cannot easily make double bonds with oxygen atoms to form a molecule of silicates. This is because silicon’s 3p orbitals are better suited to make four single bonds with each oxygen atom, rather than two bonds. As a result, it is more energetically favorable for silicon to form a network of oxygen-silicon atoms called silicates than to make two carbon-oxygen bonds with each oxygen atom as would occur in the formation of carbon dioxide.
Manufacturers use a variety of food additives, including silicon dioxide, which has the E number E551. It is added to foods as an anticaking agent that prevents ingredients from caking or sticking together in clumps. It helps the ingredients flow freely through the manufacturing process and during storage, and also protects against moisture. It is considered safe to ingest in small amounts. However, nanoparticles of silica, which are not regulated as the standard form, have been found in foods and may pose some health concerns. Silica particles can be inhaled and may reach other parts of the body, such as the kidneys and heart.