Connectivity of Atoms from Formula

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Connectivity of Atoms from Formula

Postby Drake_Everlove_1K » Fri Oct 21, 2016 10:51 pm

So, there are three different formulas I am aware of.

There is the chemical/empirical formula, the ratio of atoms to eachother in a molecule (i.e. CH4O for methanol)
The molecular formula, which represents the total number of atoms in a molecule, which happens to remain the same (CH4O) in methanol.

But there is also the structural formula, which gives us hints regarding the connectivity of atoms in a structure. If you tried to draw the lewis structure of CH4O from the molecular formula alone, it would not get you very far. Its structural formula, as per the book (page F26), is CH3OH. This gives a clearer view of how the lewis structure should be written, as Dr. Lavelle mentioned in class today. But how do we know if what is given to us is a molecular or structural formula? How can we glean the connectivity of atoms correctly from a molecular formula like CH4O?

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Re: Connectivity of Atoms from Formula

Postby Akshay_Manjarekar_3C » Sat Oct 22, 2016 2:54 pm

As per my experience, I've noticed that when an organic molecule is written ( and I'll use propane as an example here ) in it's molecular formula, it is usually written as C3H8. It's structural formula, however, is CH3CH2CH3. Usually when the molecule is written in this expanded form, it is a pretty good indicator of knowing that you are looking at the structural form. The expanded form shows you how the atoms are connected to one another. But if you are only given the molecular formula, I recommend that you use the fact that Hydrogen is never in the center, that the element with the lowest ionization energy in the center, and number of valence electrons each atom has. And to verify, check the formal charge on each atom. Also remember those cases where there are exceptions to the octet rule. Hope this helped!

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