2 improved formatting, grammar, mathjax edited Jun 21 '15 at 9:53 tschoppi 8,07644 gold badges3434 silver badges8585 bronze badges bothBoth are correct, but the second one is mostmore commonly used.Actually Actually, the way of writing a molecular formula signifies the structure of the molecule let. Let me explain you the there: There are structurescompounds that have the same molecular formula but have different structures such. Such molecules are called structural isomers. An example for exa carbon compound:this is the example of carbon compound having same molecular formula but different structure so asAs you can see that, even if both lookshave the same by formula but actually they have different structures  (they are structural isomers to be precise say it precisely) so generally. Generally formulae of many compounds or molecules are written in a way so that they can signify the structure or arrangement of atoms in molecules Now. Now look at that image again if i. If I want to write chemical formulae of both compounds that can signify theretheir structures so i will, I would write it as: first$$\ce{CH3CH2CH2Cl}$$ for the first one is : CH3CH2CH2Cl, and the second one is CH3CHClCH3 I$$\ce{CH3CHClCH3}$$. I guess now you can getunderstand that the way of writing a formula defines the structure of the compound, so always write the formula inin a way that can define or give some hint about the structure. both are correct but second one is most commonly used.Actually the way of writing molecular formula signifies the structure of molecule let me explain you the there are structures that have same molecular formula but have different structures such molecules are called structural isomers for ex:this is the example of carbon compound having same molecular formula but different structure so as you can see that even if both looks same by formula but actually they have different structures(they are structural isomers to be precise say) so generally formulae of many compounds or molecules are written in way so that they can signify the structure or arrangement of atoms in molecules Now look at that image again if i want to write chemical formulae of both compounds that can signify there structures so i will write it as: first one is : CH3CH2CH2Cl and second one is CH3CHClCH3 I guess now you can get that way of writing formula defines structure of compound so always write the formula in way that can define or give some hint about structure Both are correct, but the second one is more commonly used. Actually, the way of writing a molecular formula signifies the structure of the molecule. Let me explain: There are compounds that have the same molecular formula but have different structures. Such molecules are called structural isomers. An example for a carbon compound: As you can see, even if both have the same formula they have different structures  (they are structural isomers to say it precisely). Generally formulae of many compounds or molecules are written in a way so that they can signify the structure or arrangement of atoms in molecules. Now look at that image again. If I want to write chemical formulae of both compounds that can signify their structures, I would write: $$\ce{CH3CH2CH2Cl}$$ for the first one, and the second one is $$\ce{CH3CHClCH3}$$. I guess now you can understand that the way of writing a formula defines the structure of the compound, so always write the formula in a way that can define or give some hint about the structure. 1 answered Jun 21 '15 at 8:31 user17052 11022 bronze badges both are correct but second one is most commonly used.Actually the way of writing molecular formula signifies the structure of molecule let me explain you the there are structures that have same molecular formula but have different structures such molecules are called structural isomers for ex:this is the example of carbon compound having same molecular formula but different structure so as you can see that even if both looks same by formula but actually they have different structures(they are structural isomers to be precise say) so generally formulae of many compounds or molecules are written in way so that they can signify the structure or arrangement of atoms in molecules Now look at that image again if i want to write chemical formulae of both compounds that can signify there structures so i will write it as: first one is : CH3CH2CH2Cl and second one is CH3CHClCH3 I guess now you can get that way of writing formula defines structure of compound so always write the formula in way that can define or give some hint about structure