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What is the meaning of brackets in chemical equations?

For example, if there was a compound (i don't know if it exists - its just an example) like 2NaCl(OH2)4 (the last 2 and 4 are supposed to be in subscript). How many atoms are there of every element present in the above substance.And why is the bracket used? Please Explain what the bracket means.Thanks a lot!! :)


Brackets In Chemical Equations
Absolutely it is not exist. Hahaha For example Mg(NO3)2 [ it does exist ^^ ] It means Magnesium atom have 2 molecules of NO3 related to its valency electron. It means (again) in substance molecule we can find 1 Mg, 2 Nitrogen, and 6 oxygen
Lets look at your imaginary molecule: The OH2 : This means that you have a group which consists of 1 oxygen atom attached to 2 hydrogen atoms. Now in this imaginary molecule, 4 of these OH2 groups have to be attached to 1 NaCl group. How are you going to write this so that everybody understands what you mean? Let us imagine that you write: NaCIOH24. This could very easily be read as 1atom Na, 1atom Cl, 1 atom O and 24 atoms H, which is not what you wanted to say. Because you want to say4 groups of OH2, you enclose the OH2 group in brackets and then put a 4 outside the bracket: This tells any other chemist exactly what you mean. Look at a real molecule: NaCl this is easy because 1atom of sodium joins to 1 atom of chlorine (technically it is said that they both have a valency of1) No brackets are needed as it is impossible to make a mistake in reading the molecule. What about a salt like aluminium sulphate: aluminium has a valency of 3 and the sulphate group has a valency of 2, so 2 Al atoms will join with 3 SO4 groups If you write Al2SO43 you have the problem above, so you write Al2(SO4)3 to be properly understood.

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