A) CH5 B)C2H6N C)C3H5Br2
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Hydrogen and halogens have 1 bond
Oxygen has two bonds
Nitrogen has three bonds
Carbon has four bonds
HONC
This is all due to the number of valance electrons they each can accept, in order to form a set of covalent bonds with their own electron config equal to that of the nearest inert gas.
To try example A. The Carbon only has four bonds. That fifth hydrogen will have nowhere to go, on the carbon. It cannot bond to any of the other hydrogens, because their bonds are already used up, in connecting to the carbon.
Example B:
Ok, let's suppose the Carbons bond to each other. A single bond. We'll try double bonds later, if we must.
The first carbon thus can accept 3 of the hydrogens.
The second carbon will accept the nitrogen and two of the hydrogens.
The nitrogen has a bond left over after accepting the final hydgogen.
Well, it seems we still have one bond left over.
Let's try a carbon-carbon double bond.
First carbon now only accepts 2 hydrogens
Second carbon accepts 1 nitrogen, and 1 hydrogen
Now the nitrogen accepts 2 hydrogens
That is only 5 hydrogens, and we still can't find a place for the remaining hydrogen to go.
You can try any config you want, but it will turn out that to make a double bond, it gets rid of the ability for TWO hydrogens, and not just one.
Example C:
First carbon, give it 3 hydrogens
Second carbon, bonded to the first, give it two hydrogens
Third carbon, bonded to the second. It requires three bonds. There are only two bromines left over to fill those bonds. We have one remaining bond.
No matter what config of double bonds we do, it will not solve the problem. Each double bond eliminates two abilities for hydrogens (or halogens) to fill in, and not one.
Oxygen has two bonds
Nitrogen has three bonds
Carbon has four bonds
HONC
This is all due to the number of valance electrons they each can accept, in order to form a set of covalent bonds with their own electron config equal to that of the nearest inert gas.
To try example A. The Carbon only has four bonds. That fifth hydrogen will have nowhere to go, on the carbon. It cannot bond to any of the other hydrogens, because their bonds are already used up, in connecting to the carbon.
Example B:
Ok, let's suppose the Carbons bond to each other. A single bond. We'll try double bonds later, if we must.
The first carbon thus can accept 3 of the hydrogens.
The second carbon will accept the nitrogen and two of the hydrogens.
The nitrogen has a bond left over after accepting the final hydgogen.
Well, it seems we still have one bond left over.
Let's try a carbon-carbon double bond.
First carbon now only accepts 2 hydrogens
Second carbon accepts 1 nitrogen, and 1 hydrogen
Now the nitrogen accepts 2 hydrogens
That is only 5 hydrogens, and we still can't find a place for the remaining hydrogen to go.
You can try any config you want, but it will turn out that to make a double bond, it gets rid of the ability for TWO hydrogens, and not just one.
Example C:
First carbon, give it 3 hydrogens
Second carbon, bonded to the first, give it two hydrogens
Third carbon, bonded to the second. It requires three bonds. There are only two bromines left over to fill those bonds. We have one remaining bond.
No matter what config of double bonds we do, it will not solve the problem. Each double bond eliminates two abilities for hydrogens (or halogens) to fill in, and not one.