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Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by chemical bonds. Chemical compounds can be molecular compounds held together by covalent bonds, salts held together by ionic bonds, intermetallic compounds held together by metallic bonds, or complexes held together by coordinate covalent bonds. Pure chemical elements are not considered chemical compounds, even if they consist of molecules which contain only multiple atoms of a single element (such as H2, S8, etc.), which are called diatomic molecules or polyatomic molecules.

Wider definitions

There are exceptions to the definition above, and large amounts of the solid chemical matter familiar on Earth do not have simple formulas. Certain crystalline compounds are called "non-stoichiometric" because they vary in composition due to either the presence of foreign elements trapped within the crystal structure or a deficit or excess of the constituent elements. Such non-stoichiometric compounds form most of the crust and mantle of the Earth.

Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which will make the ratio of elements by mass vary slightly.

Elementary concepts

Characteristic properties of compounds:

1. Elements in a compound are present in a definite proportion
Example- 2 atoms of hydrogen + 1 atom of oxygen becomes 1 molecule of compound-water.
2. Compounds have a definite set of properties
Elements of the compound do not retain their original properties.
Example- Hydrogen(element{which is combustible and non-supporter of combustion}) + Oxygen(element{which is non-combustible and supporter of combustion}) becomes Water(compound{which is non-combustible and non-supporter of combustion})
3. Elements in a compound cannot be separated by physical methods.

Valency is the number of hydrogen atoms which can combine with one atom of the element forming a compound.

Compounds compared to mixtures

The physical and chemical properties of compounds are different from those of their constituent elements. This is one of the main criteria for distinguishing a compound from a mixture of elements or other substances because a mixture's properties are generally closely related to and dependent on the properties of its constituents. Another criterion for distinguishing a compound from a mixture is that the constituents of a mixture can usually be separated by simple, mechanical means such as filtering, evaporation, or use of a magnetic force, but the components of a compound can only be separated by a chemical reaction. Conversely, mixtures can be created by mechanical means alone, but a compound can only be created (either from elements or from other compounds, or a combination of the two) by a chemical reaction.

Some mixtures are so intimately combined that they have some properties similar to compounds and may easily be mistaken for compounds. One example is alloys. Alloys are made mechanically, most commonly by heating the constituent metals to a liquid state, mixing them thoroughly, and then cooling the mixture quickly so that the constituents are trapped in the base metal. Other examples of compound-like mixtures include intermetallic compounds and solutions of alkali metals in a liquid form of ammonia.


Chemists describe compounds using formulas in various formats. For compounds that exist as molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metaloxides, the empirical formula is normally given, e.g. NaCl for table salt.

The elements in a chemical formula are normally listed in a specific order, called the Hill system. In this system, the carbon atoms (if there are any) are usually listed first, any hydrogen atoms are listed next, and all other elements follow in alphabetical order. If the formula contains no carbon, then all of the elements, including hydrogen, are listed alphabetically. There are, however, several important exceptions to the normal rules. For ionic compounds, the positive ion is almost always listed first and the negative ion is listed second. For oxides, oxygen is usually listed last.

Organic acids generally follow the normal rules with C and H coming first in the formula. For example, the formula for trifluoroacetic acid is usually written as C2HF3O2. More descriptive formulas can convey structural information, such as writing the formula for trifluoroacetic acid as CF3CO2H. On the other hand, the chemical formulas for most inorganic acids and bases are exceptions to the normal rules. They are written according to the rules for ionic compounds (positive first, negative second), but they also follow rules that emphasize their Arrhenius definitions. Specifically, the formula for most inorganic acids begins with hydrogen and the formula for most bases ends with the hydroxide ion (OH-). Formulas for inorganic compounds do not often co

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound.

The chemical formula identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol (although 18th-century books often used superscripts) and also can be combined by more chemical elements. For example, methane, a small molecule consisting of one carbon atom and four hydrogen atoms, has the chemical formula CH4. The sugar molecule glucose has six carbon atoms, twelve hydrogen atoms and six oxygen atoms, so its chemical formula is C6H12O6.

Chemical formulas may be used in chemical equations to describe chemical reactions. For ionic compounds and other non-molecular substances an empirical formula may be used, in which the subscripts indicate the ratio of the elements.

The 19th-century Swedish chemist Jöns Jakob Berzelius worked out this system for writing chemical formulas.

Molecular geometry and structural formulas

The connectivity of a molecule often has a strong influence on its physical and chemical properties and behavior. Two molecules composed of the same numbers of the same types of atoms (i.e. a pair of isomers) might have completely different chemical and/or physical properties if the atoms are connected differently or in different positions. In such cases, a structural formula can be useful, as it illustrates which atoms are bonded to which other ones. From the connectivity, it is often possible to deduce the approximate shape of the molecule.

A chemical formula supplies information about the types and spatial arrangement of bonds in the chemical, though it does not necessarily specify the exact isomer. For example ethane consists of two carbon atoms single-bonded to each other, with each carbon atom having three hydrogen atoms bonded to it. Its chemical formula can be rendered as CH3CH3. In ethylene there is a double bond between the carbon atoms (and thus each carbon only has two hydrogens), therefore the chemical formula may be written: CH2CH2, and the fact that there is a double bond between the carbons is implicit because carbon has a valence of four. However, a more explicit method is to write H2C=CH2 or less commonly H2C::CH2. The two lines (or two pairs of dots) indicate that a double bond connects the atoms on either side of them.

A triple bond may be expressed with three lines or pairs of dots, and if there may be ambiguity, a single line or pair of dots may be used to indicate a single bond.

Molecules with multiple functional groups that are the same may be expressed by enclosing the repeated group in round brackets. For example isobutane may be written (CH3)3CH. This semi-structural formula implies a different connectivity from other molecules that can be formed using the same atoms in the same proportions (isomers). The formula (CH3)3CH implies a central carbon atom attached to one hydrogen atom and three CH3 groups. The same number of atoms of each element (10 hydrogens and 4 carbons, or C4H10) may be used to make a straight chain molecule, butane: CH3CH2CH2CH3.

The alkene but-2-ene has two isomers which the chemical formula CH3CH=CHCH3 does not identify. The relative position of the two methyl groups must be indicated by additional notation denoting whether the methyl groups are on the same side of the double bond (cis or Z) or on the opposite sides from each other (trans or E).


For polymers, parentheses are placed around the repeating unit. For example, a hydrocarbon molecule that is described as CH3(CH2)50CH3, is a molecule with fifty repeating units. If the number of repeating units is unknown or variable, the letter n may be used to indicate this formula: CH3(CH2)nCH3.


For ions, the charge on a particular atom may be denoted with a right-hand superscript. For example Na+, or Cu2+. The total charge on a charged molecule or a polyatomic ion may also be shown in this way. For example: hydronium, H3O+ or sulfate, SO42−.

For more complex ions, brackets [ ] are often used to enclose the ionic formula, as in [B12H12]2−, which is found in compounds such as Cs2[B12H12]. Parentheses ( ) can be nested inside brackets to indicate a repeating unit, as in [Co(NH3)6]3+. Here (NH3)6 indicates that the ion contains six NH<

Empirical formula

In chemistry, the empirical formula of a chemical compound is the simplest whole number ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic compounds, such as CaCl2, and for macromolecules, such as SiO2. The term empirical refers to the process of elemental analysis, a technique of analytical chemistry used to determine the relative amounts of each element in a chemical compound.

In contrast, the molecular formula identifies the number of each type of atom in a molecule, and the structural formula also shows the structure of the molecule.

For example, the chemical compound n-hexane has the structural formula CH|3|CH|2|CH|2|CH|2|CH|2|CH|3, which shows that it has 6 carbon atoms arranged in a straight chain, and 14 hydrogen atoms. Hexane's molecular formula is C|6|H|14, and its empirical formula is C|3|H|7, showing a C:H ratio of 3:7. Different compounds can have the same empirical formula. For example, formaldehyde, acetic acid and glucose have the same empirical formula, CH|2|O. This is the actual chemical formula for formaldehyde, but acetic acid has double the number of atoms and glucose has six times the number of atoms.

Examples of common substances

Use in physics

In physics, an empirical formula is a mathematical equation that predicts observed results, but is derived from experiment or conjecture and not directly from first principles.

An example was the Rydberg formula to predict the wavelengths of hydrogen spectral lines. Proposed in 1888, it perfectly predicted the wavelengths of the Lyman series, but lacked a theoretical basis until Niels Bohr produced his Bohr model of the atom in 1913.

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solidchemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon such as diamond and graphite, are considered inorganic. The distinction between "organic" and "inorganic" carbon compounds, while "useful in organizing the vast subject of chemistry... is somewhat arbitrary".

Organic chemistry is the science concerned with all aspects of organic compounds. Organic synthesis is the methodology of their preparation.



The name "organic" is historical, dating back to the 1st century. For many centuries, Western alchemists believed in vitalism. This is the theory that certain compounds could only be synthesized from their classical elements — Earth, Water, Air and Fire — by action of a "life-force" (vis vitalis) possessed only by organisms. Vitalism taught that these "organic" compounds were fundamentally different from the "inorganic" compounds that could be obtained from the elements by chemical manipulation.

Vitalism survived for a while even after the rise of modern atomic theory and the replacement of the Aristotelian elements by those we know today. It first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A more decisive experiment was Wöhler's 1828 synthesis of urea from the inorganic saltspotassium cyanate and ammonium sulfate. Urea had long been considered to be an "organic" compound as it was known to occur only in the urine of living organisms. Wöhler's experiments were followed by many others, where increasingly complex "organic" substances were produced from "inorganic" ones without the involvement of any living organism.

Modern classification

Even after vitalism had been disproved, the distinction between "organic" and "inorganic" compounds has been retained through the present. The modern meaning of "organic compound" is any one of them that contains a significant amount of carbon - even though many of the "organic compounds" known today have no connection whatsoever with any substance found in living organisms.

There is no "official" definition of an organic compound. Some text books define an organic compound as one containing one or more C-H bonds; others include C-C bonds in the definition. Others state that if a molecule contains carbon it is organic.

Even the broader definition of "carbon-containing molecules" requires the exclusion of carbon-containing alloys (including steel), a relatively small number of carbon-containing compounds such as metal carbonates and carbonyls, simple oxides of carbon and cyanides, as well as the allotropes of carbon and simple carbon halides and sulfides, which are usually considered to be inorganic.

The "C-H" definition excludes compounds which are historically and practically considered to be organic. Neither urea nor oxalic acid are organic by this definition, yet they were two key compounds in the vitalism debate. The IUPAC Blue Book on organic nomenclature specifically mentions urea and oxalic acid. Other compounds lacking C-H bonds that are also traditionally considered to be organic include benzenehexol, mesoxalic acid, and carbon tetrachloride. Mellitic acid, which contains no C-H bonds, is considered to be a possible organic substance in Martian soil. All do, however, contain C-C bonds.

The "C-H bond only" rule also leads to somewhat arbitrary divisions in sets of carbon-fluorine compounds, as for example Teflon is considered by this rule "inorganic" but Tefzel organic; similarly many Halons are considered inorganic while the rest are organic. For these and other reasons, most sources consider C-H compounds to be only a subset of "organic" compounds.

To summarize: Most carbon-containing compounds are organic, and most compounds with a C-H bond are organic. Not all organic compounds necessarily contain C-H bonds (e.g. urea).


SeeClassification of organic compounds

Organic compounds may be classified in a variety of ways. One major distinction is between natural and synthetic compounds. Organic compounds can also be classified or subdivided by the presence of heteroatoms, e.g. organometallic compounds which feature bonds between carbon and a metal, and From Yahoo Answers


Answers:I will keep it simple Water H2O Table salt NaCl Carbon dioxide CO2

Question:Write the chemical formula for the binary ionic compound made from the two elements listed in each example below. A. Na and S B. Sr and S C. Mg and F D. Na and N

Answers:Na2S Sodium sulfide SrS Strontium Sulfide MgF2 Magnesium Fluoride Na3N Sodium Nitride

Question:Okay, so for Chemistry class I have to name a list of compounds and provide their chemical formulas. I am a bit confused, I am going to give an example and if someone could help me understand how I find the compound name and chemical formula that would be wonderful! What is the name and chemical formula for: aluminum(+3) and bromine(-1) If you could explain how I can figure it out on my own, that would be great as well :) Thanks!

Answers:Al is correct for Aluminium and Br is correct for Bromine...as found in the Periodic Table of Elements. (The Al(+3) and Br(-1) indicate the 'Valence' (reactive electrons) in the elements. To react Al with Br we need 1 ion of Al(+3) to react with 3 ions of Br(-1) in order to produce a neutral compound of Aluminium bromide...Al(+3) + 3 x Br(-1) ===> AlBr3.

Question:Name Chemical Compounds that could be found in a House. for example, bricks,cable lines, cement. Please name and compound and state where they can be found in a house. Person with the longest list of Chemical Compounds will get best answer!! I need the Formula compound too. with the elements. It is best if its has to do with the construction of the house and not just household items.

Answers:NaCL - table salt NiCd - computer and other rechargeable batteries Zn2MnO2 - alkaline batteries CaCO3 - Rolaids/Tums/calcium suppliments and concrete (!!!) C6H10O5 - Cellulose (no, not cellulite!) plants, paper, etc 2-aminopentanedioic acid, 2-aminoglutaric acid, 1-aminopropane-1,3-dicarboxylic acid (Monosodium Glutamate) SiGe - semiconducters found in, well, everything acetylsalicylic acid - Aspirin Carbonic acid - Soda pop Sulfuric acid - Drain clearing chemicals Ammonia - cleaning agents CH3CH2CH2CH3 - Butane, found in cigarette lighters CH3CH2CH3 - Propane, found in your outdoor gas grill C6H6 - Benzene found in the gasoline in your vehicle C7H8 - Toluene, also found in the gasoline in your vehicle C10H8 - Napthalene, found in mothballs which are found in closets CaSO4-2(H2O) - Gypsum, found in wallboard, plaster and paint filler Could keep going, but...why?

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Formulas for Chemical Compounds :Learn about formulas for chemical compounds