Chemical substances are often called 'pure' to set them apart from mixtures. Webarchive template wayback links. From Wikipedia, the free encyclopedia. References in classic literature?
However, the polymer may be defined by a known precursor or reaction s and the molar mass distribution. The concept of a "chemical substance" became firmly established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate. However, there are some controversies regarding this definition mainly because the large number of chemical substances reported in chemistry literature need to be indexed.
Isomerism caused much consternation to early researchers, since isomers have exactly the same composition, but differ in configuration arrangement of the atoms.
For example, there was much speculation for the chemical identity of benzene , until the correct structure was described by Friedrich August Kekulé. Likewise, the idea of stereoisomerism - that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement - was another crucial step in understanding the concept of distinct chemical substances.
For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction.
This is so, because all of the atoms in a sample of an element have the same number of protons, though they may be different isotopes , with differing numbers of neutrons. As of , there are known elements, about 80 of which are stable — that is, they do not change by radioactive decay into other elements. Some elements can occur as more than a single chemical substance allotropes. For instance, oxygen exists as both diatomic oxygen O 2 and ozone O 3. The majority of elements are classified as metals.
These are elements with a characteristic lustre such as iron , copper , and gold. Metals typically conduct electricity and heat well, and they are malleable and ductile. Non-metals lack the metallic properties described above, they also have a high electronegativity and a tendency to form negative ions. Certain elements such as silicon sometimes resemble metals and sometimes resemble non-metals, and are known as metalloids.
A pure chemical compound is a chemical substance that is composed of a particular set of molecules or ions. Two or more elements combined into one substance through a chemical reaction form a chemical compound.
All compounds are substances, but not all substances are compounds. A chemical compound can be either atoms bonded together in molecules or crystals in which atoms, molecules or ions form a crystalline lattice. Compounds based primarily on carbon and hydrogen atoms are called organic compounds , and all others are called inorganic compounds. Compounds containing bonds between carbon and a metal are called organometallic compounds.
Compounds in which components share electrons are known as covalent compounds. Compounds consisting of oppositely charged ions are known as ionic compounds, or salts. In organic chemistry, there can be more than one chemical compound with the same composition and molecular weight.
Generally, these are called isomers. Isomers usually have substantially different chemical properties, and often may be isolated without spontaneously interconverting. A common example is glucose vs. The former is an aldehyde , the latter is a ketone. Their interconversion requires either enzymatic or acid-base catalysis. However, tautomers are an exception: A common example is glucose , which has open-chain and ring forms.
One cannot manufacture pure open-chain glucose because glucose spontaneously cyclizes to the hemiacetal form. All matter consists of various elements and chemical compounds, but these are often intimately mixed together.
Mixtures contain more than one chemical substance, and they do not have a fixed composition. In principle, they can be separated into the component substances by purely mechanical processes. Butter , soil and wood are common examples of mixtures. Grey iron metal and yellow sulfur are both chemical elements, and they can be mixed together in any ratio to form a yellow-grey mixture.
No chemical process occurs, and the material can be identified as a mixture by the fact that the sulfur and the iron can be separated by a mechanical process, such as using a magnet to attract the iron away from the sulfur.
The resulting compound has all the properties of a chemical substance and is not a mixture. Iron II sulfide has its own distinct properties such as melting point and solubility , and the two elements cannot be separated using normal mechanical processes; a magnet will be unable to recover the iron, since there is no metallic iron present in the compound.
While the term chemical substance is a precise technical term that is synonymous with chemical for chemists, the word chemical is used in general usage in the English speaking world to refer to both pure chemical substances and mixtures often called compounds ,  and especially when produced or purified in a laboratory or an industrial process.
In countries that require a list of ingredients in products, the "chemicals" listed are industrially produced "chemical substances". The word "chemical" is also often used to refer to addictive, narcotic, or mind-altering drugs. Within the chemical industry, manufactured "chemicals" are chemical substances, which can be classified by production volume into bulk chemicals, fine chemicals and chemicals found in research only:.
The cause of the difference in production volume is the complexity of the molecular structure of the chemical. Bulk chemicals are usually much less complex.
While fine chemicals may be more complex, many of them are simple enough to be sold as "building blocks" in the synthesis of more complex molecules targeted for single use, as named above. The production of a chemical includes not only its synthesis but also its purification to eliminate by-products and impurities involved in the synthesis. The last step in production should be the analysis of batch lots of chemicals in order to identify and quantify the percentages of impurities for the buyer of the chemicals.
There are, however, some other definitions e. A pure substance cannot be separated into simpler components without chemical change. Physical changes can alter the state of matter but not the chemical identity of a pure substance. Chemical Symbol or Formula. This is one of a series of simple pages introducing key concepts in introductory chemistry. Other pages in this section include elements, mixtures and compounds and individual pages about substances , elements , mixtures and compounds , plus pages about atoms , molecules and isotopes.
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To achieve this it is is necessary to genuinely try many subjects. Also on this website: What is Organic Chemistry? What is Inorganic Chemistry? What is an element? What is a compound? What is a mixture? What is a substance? What is an atom? What is a molecule?
A chemical substance is a form of matter having constant chemical composition and characteristic properties ·. It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or . explosive - a chemical substance that undergoes a rapid chemical change (with the production of gas) on being heated or struck material, stuff - the tangible substance that goes into the makeup of a physical object; "coal is a hard black material"; "wheat is the stuff they use to make bread. chemical substance Pharmacology Any substance including alcohol, drugs, or medications–eg, those taken pursuant to a valid prescription for legitimate medical purposes, and in accordance with the prescriber's direction, as well as those taken illegally. See Substance abuse.