For years now I've wished there was a good science spelling dictionary in MS Word, and have even had discussions about how MS has really dropped the ball be essentially having no science/engineering version available. I've used the add feature in Word to build my own, but it's tedious and every now and again the custom dictionary file ends up getting lost or erased when a major incident takes place or I swap/upgrade computers. For some reason I never remember to back that shit up.
Azmanam, an enterprising grad student, went to the effort to create his own decent list, he developed it and collaborated with Antony Williams of chemspider.com to further increase the volume to ~104,000 words!
If you want this little gem go to www.chemistry-blog.com/dictionary, read about it, and download it.
I tried the instructions included in the zip, and some of the tips on the site with no success. Being trapped with a relatively old Mac at work is not helpful some days. To work around the issue, and greatly simplify things, I opened the new file and the existing custom dictionary, copied the contents of the new file, pasted into the old dictionary, saved, and was done.