A chemical substance is any material with a definite chemical composition, no matter where it comes from. Hill, J. W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry, 4th ed., p5, Pearson Prentice Hall, Upper Saddle River, New Jersey, 2005. For example, a sample of water has the same properties and the same ratio of hydrogen and oxygen whether the sample is isolated from a river or made in a laboratory. A pure substance cannot be separated into other substances by any mechanical process,Ebbing, D. D.; Gammon, S. D. General Chemistry, 7th ed., p12, Houghton Mifflin, Boston, Massachusetts, 2002.. Typical chemical substances found in the home are water, salt (sodium chloride) and sugar (sucrose). Generally, substances exist as solid, liquid, or gas, and may change between these phases of matter with changes in temperature or pressure.

The concept of chemical substances was established in the eighteenth century by the chemist Joseph Proust. He did careful studies of the composition of some pure chemical compounds such as basic copper carbonate Hill, J. W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry, 4th ed., p37, Pearson Prentice Hall, Upper Saddle River, New Jersey, 2005. He deduced that: "All samples of a compound have the same composition; that is, all samples have the same proportions, by mass, of the elements present in the compound". This became known as the law of constant composition, and it is one of the foundations of modern chemistry.

Elements

---

More on [ Chemical substance ]

ACS Matters Weekly Newsletter

FEATURE: Free Online Access to Meeting Presentations
Tue, 03 Nov 2009 13:30:00 -0500
More than 14,000 of your colleagues participated in the 238th ACS National Meeting in Washington, DC, back in August, and they were part of a dynamic and diverse gathering. If you weren't able to attend the Washington national meeting in person, you can still benefit from the scientific exchange at the meeting, because you can still view 150 of the top oral presentations from the meeting online, for free! These high-quality presentations - covering hot topics from alternative energy to environmental science, chemical consulting to social networking - feature PowerPoint slides synched with audio. You can also jump directly to a particular slide in a presentation.
Down, But Not Out
Tue, 03 Nov 2009 13:30:00 -0500
To quote the annual "Employment Outlook" in this week's edition of C&EN, "chemistry jobs took a beating this year, prompting out-of-work chemists to reinvent themselves." If this sounds familiar to you, and you find yourself in the process of reinventing yourself, we hope you'll benefit from the broad perspective on the current employment environment described in C&EN this week, and take advantage of the many career and employment services and tools that ACS provides. Visit the ACS Careers web site for links to online job listings, salary surveys and statistics, career counseling, professional development courses, and much more.
Salaries Snapshot: Employment Dashboard
Tue, 03 Nov 2009 13:30:00 -0500
The ACS Employment Dashboard is a new online tool that allows you to examine results from ACS employment surveys. It provides an overview of salaries, demographics, and employment information nationwide or by geographic region. You can also review data from previous years' surveys, to give you a sense of trends in the employment environment. Try out the ACS Employment Dashboard today, and please let us know what you think.
C&EN Webinar on R-Group Screening
Tue, 03 Nov 2009 13:30:00 -0500
Join C&EN on November 19, 11:00 AM-12:00 noon EST, for a live webinar on "R-Group Virtual Screening: A New CADD Capability for Lead Optimization," covering technology that provides new ideas and rank order based on existing information. Participants will learn about 3D QSAR that automates the creation of models for predicting the biological activity or properties of compounds, exceptionally fast 3D virtual screening for R groups based on both shape and pharmacophore similarity, and combining these technologies to find novel R-groups predicted to have high potency, optimize multiple parameters, and get hundreds of new, highly promising R-group ideas.
This Week: Online Forum on Financial or Business Questions
Tue, 03 Nov 2009 13:30:00 -0500
If you've got questions about your business and its finances, join us tomorrow for the next live discussion on the ACS Network's "Dear Adviser" forum. You can post your questions on the forum any time, then log in tomorrow, Nov. 4th, 2:00-3:00 PM EST, to participate in the discussion with Paul Hodges, chairman of chemical-industry consultants International eChem and author of the "Chemicals and the Economy" blog. In the Dear Adviser forum, you'll also find posts from other industry professionals facing financial and business questions just like you; you can post your own questions, and offer your comments or advice on issues confronting other entrepreneurs.

Patent Watch, a product of the American Chemical Society

Oxidize benzene cleanly to phenol.
Tue, 27 Oct 2009 14:23:52 -0400
Oxidize benzene cleanly to phenol.

Chemical & Engineering News: Latest News

Merck KGaA Leads OLED Consortium
Tue, 03 Nov 2009 08:30:00 -0500
Illuminating Technology: German alliance will develop soluble materials for lighting applications.
Light Commands Ion Channel
Mon, 02 Nov 2009 17:00:00 -0500
Chemical Biology: Photosensitive reaction opens or shuts potassium's flow.
Sparking A Sign Of Life
Mon, 02 Nov 2009 10:35:00 -0500
Crystal Growth: Specialized light source drives formation of optically pure amino acid derivatives.

chemicalbusiness - Twitter Search


Subscribe to Chemicals RSS feed