STRUCTURING AND WRITING A SCIENTIFIC ARTICLE:
There is an excellent article called "11 Steps to Structuring a Science Paper Editors Will Take Seriously". The author goes in depth about not only how to structure the paper, but details about what should go into each section and how those sections should be formatting. He goes into great detail while still being concise and readable.
One example of his suggestions is that when writing the paper one should write the paper in the following order: figures and tables, methods, results, discussion, conclusion, introduction, abstract, title, keywords, acknowledgements, references. This is counterintuitive considering this is not the order in which the paper is ultimately organized, but he discusses why this order helps you in making your writing clear and coherent.
Another useful resource is Southwestern University's Guide to Writing in Chemistry. This short guide gives an overview of literature in chemistry, the parts of a research article (which can differ slightly from the organization of the typical scientific research article).
The Royal Society of Chemistry provides a template for writing a research article for their journals. This can give you something concrete to work with in the format of a real scientific article. Check with your professor if he wants you to follow these guidelines. They are designed for specific journals so they may not be the format that he wishes.
Writing Guides--Writing in the Sciences (Colorado State University): This set of webpages walks you through how to write abstracts, review papers, scientific papers, policy statements, and posters among other things. It gives you tips on how to do these things well.
Graduate Scientific Writing Resource (Duke University): This website provides a guide to effective writing in the sciences. It is not meant as a step by step guide through the types of scientific writing. Rather, it is designed to teach you to make your writing more clear and effective for your audience. There are little exercises with the lessons to help you practice what you learn.
ABSTRACTS:
In particular, you might be asked to write an abstract from a paper. You do not go about it the way you might write a paper--just writing it fairly freeform. It follows a fairly strict construction based on the text and is used to introduce your readers to the paper and advertise it in collections and databases. Here are a few websites that go into detail about writing your abstract:
The Writing Center at UNC-Chapel Hill--Abstracts
How to Write a Good Abstract for a Scientific Paper or Conference Presentation