formula, in chemistry

formula, in chemistry, an expression showing the chemical composition of a compound compound, in chemistry, a substance composed of atoms of two or more elements in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound is often represented by its chemical formula .
..... Click the link for more information. . Formulas of compounds are used in writing the equations (see chemical equations chemical equation, group of symbols representing a chemical reaction .

Basic Notation Used in Equations

The chemical equation 2H₂+O₂→2H₂O represents the reaction of hydrogen and oxygen to form water.
..... Click the link for more information. ) that represent chemical reactions chemical reaction, process by which one or more substances may be transformed into one or more new substances. Energy is released or is absorbed, but no loss in total molecular weight occurs.
..... Click the link for more information. . Compounds are combinations in fixed proportions of the chemical elements element, in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound can be decomposed into its constituent elements by means of a chemical reaction, but no further simplification can be achieved.
..... Click the link for more information. . The smallest unit of an element is the atom atom [Gr.,=uncuttable (indivisible)], basic unit of matter ; more properly, the smallest unit of a chemical element having the properties of that element.

Structure of the Atom

..... Click the link for more information. .

Formulas for Compounds

The formula of a well-known compound, water, is H₂O. Water is made up of molecules, and the formula shows that each molecule consists of two atoms of hydrogen, H, bonded to an atom of oxygen, O. The subscript 2 indicates that there are two atoms of hydrogen in the molecule; where no subscript appears, as after the O, the subscript 1 is implied. It should be kept in mind that not all compounds are molecular. For example, sodium chloride, NaCl, is an ionic rather than a molecular compound. Solid sodium chloride consists of a collection of sodium ions and chloride ions arranged in a regular, three-dimensional pattern called a crystalline structure. One cannot say that a certain sodium ion and a certain chloride ion are grouped together into a unit, since each sodium ion is equally associated with all its neighboring chloride ions and each chloride ion is equally associated with all its neighboring sodium ions. The formula NaCl, therefore, cannot be taken as showing the composition of some particular unit, such as a molecule. Rather, it shows the proportion of the atoms of each element making up the compound—in this case, one atom of sodium to every atom of chlorine; such a formula is called an empirical formula.

Molecular and Empirical Formulas

If a compound is molecular, the molecular formula is preferred to the empirical formula since it gives more information. A molecule of glucose, for example, consists of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. Its molecular formula, C₆H₁₂O₆, displays this information explicitly; the empirical formula is CH₂O. From the formula one can also deduce the proportion of the atoms of each element making up the compound: one atom of carbon to every two atoms of hydrogen to every one atom of oxygen (6 : 12 : 6=1 : 2 : 1). The empirical formula of glucose, CH₂O, shows only the proportion, not the actual number of atoms.

Many compounds may have the same empirical formula. For example, formaldehyde, each molecule of which consists of one carbon atom, two hydrogen atoms, and one oxygen atom, has the molecular formula CH₂O, which is identical to the empirical formula of glucose. Another example is furnished by ethyne (acetylene), whose molecular formula is C₂H₂, and benzene, whose molecular formula is C₆H₆. Both have the same empirical formula, CH.

In addition to showing the actual number of atoms, molecular formulas are also more useful than empirical formulas in that they explicitly show radicals radical, in chemistry, group of atoms that are joined together in some particular spatial structure and that take part in most chemical reactions as a single unit.
..... Click the link for more information. . For example, the molecular formula for the compound aluminum sulfate, Al₂(SO₄)₃, shows that it contains three sulfate radicals (SO₄). The empirical formula, Al₂S₃O₁₂, does not show this. When only one radical is present in the molecule, the parentheses and subscript are omitted, e.g., CuSO₄ for cupric sulfate. Other groups are also shown in molecular formulas, e.g., the water molecules in the mineral chalcanthite (blue vitriol), which consists of cupric sulfate atoms to each of which are attached five water molecules. Its molecular formula is CuSO₄·5H₂O, its empirical formula CuSO₉H₁₀.

Structural Formulas

In many cases, especially with organic compounds, even the molecular formula does not provide enough information to identify a compound, so that structural formulas are needed. For example, both ethanol (ethyl alcohol) and dimethyl ether have the molecular formula C₂H₆O (see isomer isomer (ī`səmər), in chemistry, one of two or more compounds having the same molecular formula but different structures
..... Click the link for more information. ). Their structural formulas are: In these formulas each line represents a single covalent chemical bond chemical bond, mechanism whereby atoms combine to form molecules . There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as
..... Click the link for more information. . A double bond is represented by a double line and a triple bond by a triple line. In ethene (ethylene), C₂H₄, the carbon atoms are joined by a double bond. The structural formula of ethene is: (In many representations of structural formulas, the angles of the lines indicating bonds do not necessarily have meaning.) In ethyne (acetylene), C₂H₂, the carbon atoms are joined by a triple bond. The structural formula of ethyne is:

Semistructural Formulas

Structural formulas are often simplified so that they can be written on a single line; the simplified formulas are often called semistructural formulas. The semistructural formula for ethanol is CH₃CH₂OH, or more simply C₂H₅OH. In such a semistructural formula the OH is written explicitly to indicate that the oxygen has a hydrogen bonded to it. The C₂H₅ indicates that the two carbon atoms are bonded to one another. The semistructural formula for dimethyl ether may be written CH₃OCH₃. Here the O is placed between the two carbon atoms to show that the carbons are bonded to the oxygen. A carbon often has three hydrogens bonded to it, and the H₃ is written after the C. In some cases the H₃ is written before the C for clarity; thus the formula for dimethyl ether might be written H₃COCH₃.

Electron Dot Diagrams

Dots are used in a type of formula called the electron dot diagram, where each pair of dots represents a pair of shared electrons in a covalent bond. The diagrams for ethane (CH₃CH₃), ethene, and ethyne are:

formula, in mathematics and physics

formula, in mathematics and physics, equation equation, in mathematics, a statement, usually written in symbols, that states the equality of two quantities or algebraic expressions, e.g., x+3=5. The quantity x
..... Click the link for more information. expressing a definite fixed relationship between certain quantities. The quantities are usually expressed by letters, and their relationship is indicated by algebraic symbols. For example, A=πr² is the formula for the area A of a circle of radius r, and s= 1-2at² is the formula for the distance s traveled by a body experiencing an acceleration a during a time interval t.

(1) An arithmetic expression that solves a problem. For example, (fahrenheit-32)*5/9 is the formula for converting Fahrenheit to Celsius.

(2) In spreadsheets, an algorithm that identifies how the data in a specific number of cells is to be calculated. For example, +C3*D8 means that the contents of cell C3 are to be multiplied by the contents of cell D8 and the results are to be placed where the formula is located.

1.		formula - In logic, a sequence of symbols representing terms, predicates, connectives and quantifiers which is either true or false.
2.	(language, music)	formula - FORTH Music Language. An extension of FORTH with concurrent note-playing processes. Runs on Macintosh and Atari ST with MIDI output. ["Formula: A Programming Language for Expressive Computer Music", D.P. Anderson et al Computer 24(7):12 (Jul 1991)].
3.		formula - Preprocessor language for the Acorn Archimedes, allowing inline high-level statements to be entered in an assembly program. Written in nawk.