Is the chemical structure of an amide bond (-CONH) or (-CONH2)?

The Dictionary definition of an amide is

an organic compound obtained by replacing the −OH group in acids by the −NH 2 group.

So from this, I deduced that the bond would be CONH2.

But when I searched around, I found some images that showed the bond only had one hydrogen atom, like so:

Which is the correct bond structure? I'm looking specifically at the condensation polymerization of diamine and diacarboxylic acid to form nylon.

And also, I see online that lots of bond structures (like NH2 and COOH) are prefixed with a dash, so they'd appear like -NH2 and -COOH. Is this just a personal preference, or is there a more elaborate reason behind this?

I'm currently doing the GCSEs.

Thanks

• Three types of amide - 1° 2° and 3°. -CONH2 is 1° amide, in the image it is 2° amide. If you take out that one hydrogen too you will get a 3° amide Apr 9 '16 at 7:52

Amides are derivative of carboxylic acids. It consists of 2 parts, and the bond between carbonyl carbon and nitrogen of ammonia is called is amide bond.

The bond structure of 1° amides is as shown in the figure.

What you have shown in the question is bond structure of 2° amide, which can be obtained by removing 1 hydrogen from 1° amide.

Now if you observe structure of nylon, you will see there are n numbers of 2° amides.

And also, I see online that lots of bond structures (like NH2 and COOH) are prefixed with a dash, so they'd appear like -NH2 and -COOH. Is this just a personal preference, or is there a more elaborate reason behind this?

The dash means it is Functional Group like -R means hydrocarbyl functional group, -COOH means carboxylic acid functional group, etc.

• One more question, though: why is the coefficient of the product H2O 2, as opposed to the n for every other reagent and product? Apr 10 '16 at 6:45
• @CommandoGeek one H from each both end of $\ce{H_2N-R'-NH_2}$ Apr 11 '16 at 11:08