Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: taregg on 08/11/2013 12:19:49

Title: what does monomer exactly mean..?
Post by: taregg on 08/11/2013 12:19:49

doest mean the smallest size of element atoms or does it mean the smallest  hydrocarbon compounds chain...

Title: Re: what does monomer exactly mean..?
Post by: alancalverd on 08/11/2013 12:46:12

It's the smallest molecule of a substance. Doesn't only apply to organic compounds, though they are the most commonly mentioned polymers. In fact water exists in many forms in the atmosphere, mostly as a monomer H₂O or a trimer (H₂O)₃ which accounts for its enormous and complicated infrared absorption spectrum.

Whether you refer to nitrogen N₂ or oxygen O₂ as diatomic molecules or dimers is in principle a matter of choice, but some would argue for instance that monatomic nitrogen N is much more reactive then N₂ so N₂ is a distinct molecule. On the other hand ethylene H₂C=CH₂ is clearly a molecule with much greater reactivity than polyethylene (H₂C=CH₂)_n.

Title: Re: what does monomer exactly mean..?
Post by: distimpson on 08/11/2013 13:08:23

I've always used a functional definition, the monomer is the unit that is joined (condensed) to form the polymer. For example, polymethymethacrylate:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fpslc.ws%2Fmacrog%2Fkidsmac%2Fimages%2Fpmma02.gif&hash=3318fc8ab8ede701e013f2cf4373c25d)

For a hydrocarbon like polyethylene, the monomer would be ethylene:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.innocalsolutions.com%2Ftechinfo%2Fimages%2FZeus_Chem_Resistance_img_2.jpg&hash=e058022cf0266ec31febd1d9b63c069c)

The definition can be context dependent if there is more than one way to make the same polymer.

Images from: http://pslc.ws/macrog/kidsmac/pmma.htm (http://pslc.ws/macrog/kidsmac/pmma.htm) and http://www.innocalsolutions.com/ (http://www.innocalsolutions.com/)