A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using a single line of chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas are more limiting than chemical names and structural formulas.
The simplest types of chemical formulas are called empirical formulas, which use only letters and numbers indicating atomic proportional ratios (the numerical proportions of atoms of one type to those of other types). Molecular formulas indicate the simple numbers of each type of atom in a molecule of a molecular substance, and are thus sometimes the same as empirical formulas (for molecules that only have one atom of a particular type), and at other times require larger numbers than do empirical formulas. An example of the difference is the empirical formula for glucose, which is CH2O, while its molecular formula requires all numbers to be increased by a factor of six, giving C6H12O6.
Household chemicals are non-food chemicals that are commonly found and used in and around the average household. They are a type of consumer goods, designed particularly to assist cleaning, pest control and general hygiene purposes.
Food additives generally do not fall under this category, unless they have a use other than for human consumption. Cosmetics products can partially be counted in, because even though they are not for direct application to parts of the human body, they may contain artificial additives that have nothing to do with their dedicated purpose (e.g. preservatives and fragrances in hair spray). Additives in general (e.g. stabilizers and coloring found in washing powder and dishwasher detergents) make the classification of household chemicals more complex, especially in terms of health - some of these chemicals are irritants or potent allergens - and ecological effects.
Sodium is a chemical element with the symbol Na (from Latin: natrium) and atomic number 11. It is a soft, silver-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. The free metal does not occur in nature, but instead must be prepared from its compounds; it was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Sodium is the sixth most abundant element in the Earth's crust, and exists in numerous minerals such as feldspars, sodalite and rock salt. Many salts of sodium are highly water-soluble, and their sodium has been leached by the action of water so that chloride and sodium (NaCl) are the most common dissolved elements by weight in the Earth's bodies of oceanic water.
Many sodium compounds are useful, such as sodium hydroxide (lye) for soap-making, and sodium chloride for use as a deicing agent and a nutrient (edible salt). Sodium is an essential element for all animals and some plants. In animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated. The consequent need of animals for sodium causes it to be classified as a dietary inorganic macro-mineral.
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