Chemical substance

The chemical substance sodium chloride (table salt)

A chemical substance is an element , a compound or a mixture with certain chemical and physical properties . Chemical substances are also generally referred to as substances , materials (in technology) or matter (in physics).

Definitions in chemistry

In chemistry, substances are divided into

• Basic substances ( elements or compounds ) and
• Mixtures ( preparations ).

Important basic substances in chemistry are z. B. Water , table salt ( sodium chloride ), iron and alcohol ( ethanol ); important mixtures of substances, e.g. air , hydrochloric acid and potassium hydroxide .

Each substance portion has a mass , a volume (i.e. a space requirement) and has energy . The shape of a body can also be different for the same substance (e.g. iron wire, powder, sheet, balls, wool).

A reaction scheme can be specified for the conversion of a substance into one or more other substances (a chemical reaction ) . In chemistry, the existence of substances is proven by means of detection reactions. Concrete, qualitative detection reactions - especially those from qualitative inorganic chemistry , i.e. for anions and cations - are clearly and methodically described here. The determination of the amount is carried out with the help of modern instrumental analysis methods ( instrumental analysis ).

All fabrics are of a regular nature. If substances consist of the smallest particles, they are atoms or molecules or their ions , otherwise aggregated systems such as clusters or “giant molecules” or formula units . Chemical substances are characterized by their physical properties such as density , melting point or electrical conductivity .

Definitions of the legislator

Definition of terms in hazardous substances law
EU labeling of hazardous substances	"Substance" use permitted until December 1st, 2012	"Preparation" use allowed until June 1st, 2015
GHS hazard labeling	"Material"	"Mixture"
Swiss Chemicals Ordinance	"Material"	"Preparation"
Comprises by chemical definition	Basic substances (compounds, elements)	Mixtures (homogeneous and heterogeneous)

Deviating from the above definitions for substances and mixtures that are customary in chemistry, the EU distinguishes between "substances" (these are the pure substances of the above definition, i.e. elements and compounds) and the "preparations" consisting of several substances in the case of EU hazardous substance labeling The GHS labeling can now be referred to as “mixtures”: The legislator only uses substances for what is declared in the scheme as “pure substance” (element or compound) and not as a generic term for everything. Conversely, the terms mixture or preparation do not denote a subset of substance, but are parallel terms. Since the introduction of the GHS, a different date (December 1, 2012) has applied to “substances” than to “preparations” (then “mixtures”, June 1, 2015); such a distinction would not be possible with the definition given at the beginning of the article.

Classification of chemical substances

Schematic classification of the substances

material                                                                                                                               mixture                       Pure substance                                                                                               homogeneous mixture                         connection   element                                                                                           Gas mixture Mixture of several gases   Alloy Mixture with metallic properties , contains at least one metal   Solution Solid ,  liquid , gas dissolved  in a liquid             molecular   Ionic                                                       heterogeneous mixture                                                                                                                             Foam Gaseous bubbles in a liquid   Rigid foam Gaseous bubbles in a solid   Aerosol   Suspension Solid particles in a liquid   Emulsion Mixture of several immiscible liquids   Batch mixture of several not mixable solid                                                                             Smoke Solid particles in a gas   Fog Liquid particles in a gas

Historical

In the past, substances were also referred to as chemical bodies ; In contrast to mixtures, bodies only consist of one element or one chemical compound.

Different distinctions of substances (selection)

• Hazardous substances are substances that can represent particular sources of danger, for example with the properties flammable , explosive or toxic .
• As chemical substances which have in the chemistry lab or in the chemical industry are used or produced.

Web links

• (Public) substance information system IGS of the state of North Rhine-Westphalia
• Joint substance data pool of the federal and state governments (GSBL)

Individual evidence

1. ^ "Substance" in Meyer's Large Universal Lexicon
2. ↑ Entry on chemical substance . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.C01039 Version: 2.3.3.
3. ↑ CLP regulation (PDF) , p. 9.