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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 JÃ¶ns 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, SO42âˆ’.
For more complex ions, brackets [ ] are often used to enclose the ionic formula, as in [B12H12]2âˆ’, 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<
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.
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
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.
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.
- R2C=O + :C: â†’ 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
Answers:Al2(SO4)3 For the first one: C For the second: D For the third: C
Answers:3 CH3COOH + Al(OH)3 >> Al(CH3COO)3 + 3 H2O
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.
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