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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<

Chemical equation

A chemical equation is symbolic representation of a chemical reaction where the reactant entities are given on the left hand side and the product entities on the right hand side. The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric numbers. The first chemical equation was diagrammed by Jean Beguin in 1615.


A chemical equation consists of the chemical formulas of the reactants (the starting substances) and the chemical formula of the products (substances formed in the chemical reaction). The two are separated by an arrow symbol (\rightarrow, usually read as "yields") and each individual substance's chemical formula is separated from others by a plus sign.

As an example, the formula for the burning of methane can be denoted:

CH|4| + 2 O|2| \rightarrow CO|2| + 2 H|2|O

This equation would be read as "CH four plus O two produces CO two and H two O." But for equations involving complex chemicals, rather than reading the letter and its subscript, the chemical formulas are read using IUPAC nomenclature. Using IUPAC nomenclature, this equation would be read as "methane plus oxygen yields carbon dioxide and water."

This equation indicates that oxygen and CH4 react to form H2O and CO2. It also indicates that two oxygen molecules are required for every methane molecule and the reaction will form two water molecules and one carbon dioxide molecule for every methane and two oxygen molecules that react. The stoichiometric coefficients (the numbers in front of the chemical formulas) result from the law of conservation of mass and the law of conservation of charge (see "Balancing Chemical Equation" section below for more information).

Common symbols

Symbols are used to differentiate between different types of reactions. To denote the type of reaction:

  • "=" symbol is used to denote a stoichiometric relation.
  • "\rightarrow" symbol is used to denote a net forward reaction.
  • "\rightleftarrows" symbol is used to denote a reaction in both directions.
  • "\rightleftharpoons" symbol is used to denote an equilibrium.

Physical state of chemicals is also very commonly stated in parentheses after the chemical symbol, especially for ionic reactions. When stating physical state, (s) denotes a solid, (l) denotes a liquid, (g) denotes a gas and (aq) denotes an aqueous solution.

If the reaction requires energy, it is indicated above the arrow. A capital Greek letter delta (\Delta) is put on the reaction arrow to show that energy in the form of heat is added to the reaction. h\nu is used if the energy is added in the form of light.

Balancing chemical equations

The law of conservation of mass dictates the quantity of each element does not change in a chemical reaction. Thus, each side of the chemical equation must represent the same quantity of any particular element. Similarly, the charge is conserved in a chemical reaction. Therefore, the same charge must be present on both sides of the balanced equation.

One balances a chemical equation by changing the scalar number for each chemical formula. Simple chemical equations can be balanced by inspection, that is, by trial and error. Another technique involves solving a system of linear equations.

Ordinarily, balanced equations are written with smallest whole-number coefficients. If there is no coefficient before a chemical formula, the coefficient 1 is understood.

The method of inspection can be outlined as putting a coefficient of 1 in front of the most complex chemical formula and putting the other coefficients before everything else such that both sides of the arrows have the same number of each atom. If any fractional coefficient exist, multiply every coefficient with the smallest number required to make them whole, typically the denominator of the fractional coefficient for a reaction with a single fractional coefficient.

As an example, the burning of methane would be balanced by putting a coefficient of 1 before the CH4:

1 CH|4| + O|2| \rightarrow CO|2| + H|2|O

Since there is one carbon on each side of the arrow, the first atom (carbon) is balanced.

Looking at the next atom (hydrogen), the right hand side has two atoms, while the left hand side has four. To balance the hydrogens, 2 goes in front of the H2O, which yields:

1 CH|4| + O|2| \rightarrow CO|2| + 2 H|2|O

Inspection of the last atom to be balanced (oxygen) shows that the right hand side has four atoms, while the left hand side has two. It can be balanced by putting a 2 before O2, giving the balanced equation:

CH|4| + 2 O|2| \rightarrow CO|2| + 2 H|2|O

This equation does not have any coefficients in front of CH4 and CO2, since a coefficient of 1 is dropped.

Ionic equations

An ionic equation is a chemical equation in which electrolytes are written as dissociated ions. Ionic equations are used for single and double displacement reactions that occur in aqueoussolutions. For example in the following precipitation reaction:

CaCl2(aq) + 2AgNO3(aq) \rightarrow Ca(NO3)2(aq) + 2AgCl(s)

the full ionic equation would be:

Ca2+ + 2Cl&minus; + 2Ag+ + 2NO3&minus; \rightarrow Ca2+ + 2NO3&minus; + 2AgCl(s)

and the net ionic equation would be:

2Cl&minus;(aq) + 2Ag+(aq) \rightarrow 2AgCl(s)

or, in reduced balanced form,

Ag+ + Cl&minus; \rightarrow AgCl(s)

In this aqueous reaction the Ca2+ an

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

From Yahoo Answers

Question:the chemical formula for aluminum sulfate. If you had a substance that water will not dissolve, then which of the following compounds would you choose to dissolve this substance. A. vegetable oil B. any polar substance C. any ionic substance D. none of the above will work. If a molecule is to be polar covalent A. the molecule must have polar bonds in it. B. the polar bonds must be of equal strength. C. both A and B. D. neither A nor B. A bond which consists of equal sharing of electrons is A. ionic bond B. polar covalent C. purely covalent D. polyatomic ion E. none of the above

Answers:Al2(SO4)3 For the first one: C For the second: D For the third: C

Question:what is the chemical formula for aluminum acetate? What is the balanced equation for the reaction of acetic acid with aluminum hydroxide to form water and aluminum acetate?

Answers:3 CH3COOH + Al(OH)3 >> Al(CH3COO)3 + 3 H2O

Question:im my home work i was asked to draw a lewis structure that will result from the combination of aluminum and oxygen and then write the correct neutral formula. im pretty sure i got the lewis structure right but im not sure how the formula is saposed to be writen. this is what i got Al has 3 electrons and O has 6 so therefore you need 2 Al for every 3 O 2[al]^+3 3[n(with 8 dots)]^-2 Al2O3 so is the formula saposed to be writen the first way with the brackets or is the formula the second way where you just state the number of each element?

Answers:This is a common problem among teachers of first-year chemistry. Either they just ignore the facts or they don't know any better. The catch is that it really makes no sense to talk about the Lewis structure of Al2O3 since there are no molecules of Al2O3. Aluminum oxide is a network solid in which aluminum atoms are connected to bridging oxygen atoms. The bottom line is that there is no Lewis structure because there are no discrete molecules. Al2O3 is shown here: http://upload.wikimedia.org/wikipedia/commons/c/cc/Corundum-3D-balls.png

Question:Bauxite is an aluminum ore consisting primarily of aluminum oxide. When bauxite is heated, it forms aluminum and oxygen. What is the balanced chemical equation for this reaction?

Answers:Well if you're just doing Aluminum Oxide --> Aluminum + Oxygen, then: Al2O3 --> Al + O2 To make this balanced, try to understand this chart you get by breaking down the reaction. Element / # in reactant / # in product Al / 2 / 1 O / 3 / 2 So to make it balanced, you'll want to put a 2 in front of Al2O3 because O should be even. It will double everything. Al / 4 / 1 O / 6 / 2 Now put a 4 in front of the Al in the product. Al / 4 / 4 O / 6 / 2 And a 3 in front of O2. Al / 4 / 4 O / 6 / 6 There you go! 2Al[2]O[3] --> 4Al + 3O[2] [subscript]

From Youtube

aluminum fountain :finally,my first working fountain,windy day though...this composition use aluminum.. aluminum metal info:aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth's crust, and the third most abundant element therein, after oxygen and silicon. It makes up about 8% by weight of the Earth's solid surface. Aluminium is too reactive chemically to occur in nature as a free metal. Instead, it is found combined in over 270 different minerals.[4] The chief source of aluminium is bauxite ore. Aluminium is remarkable for its ability to resist corrosion due to the phenomenon of passivation and for the metal's low density. Structural components made from aluminium and its alloys are vital to the aerospace industry and very important in other areas of transportation and building. Its reactive nature makes it useful as a catalyst or additive in chemical mixtures, including being used in ammonium nitrate explosives to enhance blast power. Aluminium is a soft, durable, lightweight, malleable metal with appearance ranging from silvery to dull grey, depending on the surface roughness. Aluminium is nonmagnetic and nonsparking. It is also insoluble in alcohol, though it can be soluble in water in certain forms. The yield strength of pure aluminium is 711 MPa, while aluminium alloys have yield strengths ranging ...

Aluminum Air Batteries :Aluminum Air BatteriesBatteries are devices converting chemical energy to receive power.They consist of two electrodes initiating chemical reactions that involve or generate electrons. The electrodes are connected to each other using a special solution called electrolyte, which helps the ions move around completing electric circuits. Electrons are produced on the anode, and they can move through the external circuit to the cathode. This is nothing more than the flow of electrons, or electric current. This phenomenon can be used to improve a whole number of simplest devices. In our case a battery can be made using these two reactions: (1) a reaction with aluminum, which generates electrons for one of the electrodes, and (2) a reaction with oxygen using the electrons on the other electrode. To help the electrons inside the battery get access to the oxygen contained in the air, we can make the second electrode using the material that can conduct electricity, but is not active, like coal, which incidentally for the most part consists of carbon. Activated carbon has lots of pores, which often provides us with a large area exposed to atmosphere. Only one gram of activated carbon can in fact appear larger in area than an entire soccer field! In this experiment we will build a battery using the two reactions discussed earlier. And the most amazing thing is - home made batteries can feed even a small motor or a light bulb! So, today we will need: aluminum foil, scissors, rulers ...