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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<

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.

Atomic carbon

Atomic carbon in chemistry is single carbon atom with chemical formula :C: - in effect a dicarbene.

This very short lived species is created by passing a large current through two adjacent carbon rods, generating an electric arc. Atomic carbon is generated in the process. Professor Phil Shevlin has done the principal work in the field based at Auburn University in the USA.

The way this species is made is closely related to the formation of fullerenes C60, the chief difference being that a much lower vacuum is used in atomic carbon formation.

This species has been used to generate "true" carbenes by the abstraction of oxygen atoms from carbonyl groups:

R2C=O + :C: → R2C: + CO

Carbenes formed in this way will exhibit true carbenic behaviour. Carbenes prepared by other methods such as diazo compounds, might exhibit properties better attributed to the diazo compound used to make the carbene (which mimic carbene behaviour), rather than to the carbene itself. This is important from a mechanistic understanding of true carbene behaviour perspective.

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:I'm a year 10 student and I have to use aluminium or iron to describe the process of carbon reduction. Could anyone please explain in a clear, easy to understand way on what carbon reduction is exactly? And is it easier to use aluminium or iron to explain it? Thank you so much! XD

Answers:Definitely use iron...direct carbon reduction of aluminum is impossible---I'll explain later. Carbon reduction has been used to obtain iron from iron oxide for centuries. Google "blast furnace" and "iron". I believe that those should answer most of your questions, or at least get you started. Aluminum production through carbon reduction is impossible because aluminum is a stronger reducing agent than carbon, and forms aluminum carbide. However, there has been mention of using carbon reduction to produce aluminum carbide, then reacting this with gaseous chlorine to give carbon tetrachloride (which can be recycled) and aluminum chloride, which can be electrolytically reduced in a sodium chloroaluminate melt, which melts much lower than cryolite (if you were using the commercial aluminum process using aluminum oxide dissolved in molten cryolite) and also takes less energy to melt the electrolyte.

Question:please show work, so i know how to do it! >.<

Answers:divide the number you're given by Avagadro's Number and multiply by the relative molecular mass of the compound (27+12+48)*2.5*10^22/6.02*10^23 = 3.61g

From Youtube

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 ...

How to Make Aluminum Nitrate Nonahydrate :How to make aluminum nitrate nonhydrate, one of the chemicals needed to make glow in the dark powder. In an upcoming video we'll need aluminum nitrate nonahydrate. The chemical formula is Al(NO3)3.9H2O Warning: These reactions must be performed outside or in a fumehood. At first it might seem that simply mixing aluminum with nitric acid can be done. But interestingly enough, aluminum is immune to the effects of nitric acid. So in order to make aluminum nitrate a two step method is needed. First the aluminum is dissolved in concentrated hydrochloric acid. This produces a solution of aluminum trichloride. The aluminum trichloride is then reacted with an excess of nitric acid. This oxidizes the nitric acid to nitrosyl chloride gas that bubbles out of solution, leaving behind aluminum nitrate. The solution is then evaporated to obtain aluminum nitrate nonahydrate. In the winter I was able to dry it in air and get crystals. But in the summer the ambient humidity was too high so I had to use a desiccator bag. www.youtube.com We'll be using aluminum nitrate nonahydrate to make glow in the dark powder in upcoming videos. More information about this reaction can be found at: sites.google.com