Examples of synonyms:

Enthalpy of Formation is also called the Heat of Formation An Extinction Coefficient is also referred to as Molar Absorptivity Redox is a common shortening of Oxidation-Reduction Reduction Potentials are also known as Electrode Potentials

If the handbook is arranged by the properties, search all synonyms of the property in the index. If the handbook has little or no indexing, the Table of Contents can be browsed for the property name(s). For handbooks that arrange the information in alphabetical order by the chemical name, look for all synonyms of the property in the information part of the entry for that chemical.

Some dictionaries that may be helpful in finding the synonyms are listed below.

For example:

Enthalpy of Formation is Thermodynamics Extinction Coefficient deals with Ultra-Violet Spectroscopy Reduction Potentials are Electrochemistry

If the handbook is arranged by the properties, look up the subject in the index; if there is little or no indexing, the Table of Contents can be browsed for that subject. For handbooks that are arranged in alphabetical order by chemical name, see if the information part of the entry is divided into subject sections.

Some dictionaries that may list the subject of the term are given below.

Recommended Dictionaries

McGraw-Hill Dictionary of Chemistry. QD5 .M357 1997 Science Reference Gives synonyms and subject field of the properties. Not good for finding symbols or units of a property. Other chemistry dictionaries are on the same shelf as this title. McGraw-Hill Dictionary of Physics. QC5 .M424 1997 Science Reference Gives synonyms and subject field of the properties. Not good for finding symbols or units of a property. Other physics dictionaries are on the same shelf as this title. Dictionary of Chemistry. QD5 .D493x 2000 Science Reference Gives synonyms, long descriptions for the property. Usually gives symbol/units. Generally does not give the subject area. Other chemistry dictionaries are on the same shelf as this title. CRC Handbook of Chemistry and Physics http://www.asu.edu/lib/resources/db/crcchem.htm See Section/Chapter 2 for defintions of scientific terms, plus symbols and terminology for physical and chemical quantities. Harcourt Academic Press Dictionary of Science and Technology http://www.harcourt.com/dictionary/ Good source for finding the subject area. Includes some synonyms. Symbols/units are usually not given. Not as comprehensive a source as dictionaries devoted to one specific subject.

The 109+ elements are the "building blocks" of chemicals. The elements are usually displayed in a periodic table that links elements with similar characteristics in vertical and horizontal rows. Each element has a one or two letter symbol; one letter symbols are always in upper case (ex. K, P, S); two letter symbols are always written with the first letter in upper case and the second letter in lower case (ex. Ar, Co, Na) . Many symbols are derived from foreign languages so the element symbol and the English name do not always match (ex. the symbol for silver is Ag from the Latin "argentum").

Chemical elements combine together to form chemical compounds. There are over 27 million substances identified by Chemical Abstracts Service. (See the latest substance count) But its not just the sheer volume of possible compounds that makes chemistry so challenging, it's also the various ways in which these chemical compounds can be identified. The four ways are: molecular forumula, structure diagrams, names, and registry numbers.

Molecular formulas describe what elements, and how many of each, make up a compound. Because the formula only accounts for what elements are present and not how those elements are arranged, it is possible for more than one compound (in some cases, hundreds!) to have the same formula. Almost all chemistry handbooks and databases provide an index by molecular formula; however most non-chemistry handbooks/databases do not.

How a molecular formula is written and how it appears in an index depends upon the type of compound.

• Organic compounds (compounds containing carbon)
  Formulas are always written and almost always indexed with the carbon (C) and hydrogen (H) first and everything else in alphabetical order.

  Examples of organic molecular formulas:

  C2HF C6H6Cl6 C11H9Br

  C9H11NO C12H10Cl2Si C18H15O4P

  
  
• Inorganic compounds (compounds that do not contain carbon)
  Formulas are written in various formats, however when indexed, they are usually put in alphabetical order.

  Examples of inorganic molecular formulas:

  Written	Indexed
  KBr	BrK
  SO2Cl2	Cl2OS2
  Pb(H2PO2)2	H4O4 P2Pb

Searching molecular formulas in databases can be tricky.

• In chemistry databases, look for a field, index or search box specifically designated for molecular formula searching. The numerical subscripts are usually typed on the same line, e.g., "c6h12o6". When carbon (C) is present, the formula should be entered with the carbon (C) and hydrogen (H) first, and with all other elements in alphabetical order. When carbon (C) is not present, the elements should be entered in alphabetical order. Be aware that some databases require mixed case, e.g., "Si2Sr" instead of "si2sr".

• In non-chemistry databases, it is best to search for both the molecular formula and the common name of the compound. The formula should be entered in lower case with the numerical subscripts in-line, and the elements in the order that would most commonly be written e.g., "srsi2", unless the database's help page indicates differently.

Because molecular formulas may not be unique, structure diagrams are used to identify specific compounds. The diagrams show not only what elements are present, but how they are arranged and connected. Structure diagrams may be written in a line or displayed in 2- or 3-dimensional graphics.

Examples of structure diagrams:

Some databases contain structure drawing programs that allow for searching by structure. Because each program may have it's own set of rules and because structure diagrams can be draw in various ways, it is not always obvious how to draw a structure so that it will be correctly interpreted by the database. For those without training in structure drawing, it may be more beneficial (and time economical) to translate the structure into a molecular formula and search by the formula.

Chemical compounds are most often identified by name; unfortunately, each compound may have many different names. Most handbooks and databases provide access by several names for each compound but each resource may not index all the variant names. There is no way to tell a head of time which name(s) will be used. Names for chemicals are grouped into 3 categories: tradenames, common names (also called generic or trivial names) and chemical (scientific) names.

There are many chemcial registries that exist, mainly for toxicological/hazard reporting to governmental agencies. The most prominent of these registries is the Chemical Abstracts Service Registry. Most recent chemical handbooks and databases index CAS registry numbers.

CAS registry numbers look like this:

528-23-4 80656-12-8 2146-37-4

26530-20-1 3973-62-4 31720-69-1

A CAS registry number is assigned to each specific chemical compound that appears in the chemical literature or as requested by chemical manufacturers to comply with regulatory procedures. Each number always has 3 segments separated by hyphens. The first segment consists of 2 or more numbers which are assigned more or less sequentially; a lower number indicates the compound was registered towards the begininng (1965) and a higher number is more recent. The second segment always is composed of 2 numbers and the third segment is always composed of one number. CAS has a formula to determine if a registry number is plausible, see: Check Digit Verification of CAS Registry Numbers at http://www.cas.org/EO/checkdig.html.

Sometimes CAS registry numbers are followed by P, D, DP or *.

• Unless you are searching the Chemical Abstracts database, ignore the P, D and DP indicators. These are "limiting codes" that restrict searches to the preparation (P), unspecified derivatives (D) or preparation of unspecified derivatives (DP) for the compound represented by that registry number.

• The * indicator, however, is important whether searching Chemical Abstracts, handbooks or databases. In the United States, chemical manufacturers are required by law to maintain a "Material Safety Data Sheet" on the substances they produce. A MSDS must include the CAS Registry number for that substance. But some substances are a mixture of unknown/unspecified compounds or have a formulation that may change with each batch or with manufacturer(for example, gasoline); in these instances, Chemical Abstracts Service assigns a registry number with an * so that the substance can be registered but the number is not generally used for searching purposes. Consequently, it may be futile to use this number when searching chemical resources; if anything at all is found, it's usually only to indicate that the substance is a mixture of unspecified compounds. The best place to find information on an * compound is usually the manufacturer's MSDS or go directly to the manufacturer.

Because a number is easier and less time consuming to search in an index than a long list of variant names or a complex chemical name, use CAS registry numbers to search more efficiently. CAS registry numbers are found in many chemistry resources including Chapters 3 (Organic Compounds) and 4 (Inorganic Compounds) of the CRC Handbook and Chemical Abstracts. There are two caveats when using registry numbers for searching purposes. Sometimes Chemical Abstracts Service changes the registry number - handbooks and databases do not always record these changes. Also, numbers are easily misinterpreted - they could be copied wrong, have numbers transposed, or be written illegibly (1 mistaken for 7, 9 mistaken for 4, etc.). Always be prepared to back up a search by registry number with a search by name or molecular formula.