page_title: Chemistry
section_title: Modern principles
hierarchical_section_title: Chemistry / Modern principles
caption_attribution_description: Alemannisch: Chemikaliäfläschä (drunder diä vo Salmiakgeist und Salpetersüri), i verschidänä Farbä belüchtät العربية: مركبات كيميائية في قوارير مخبرية (منها هيدروكسيد الأمونيوم وحمض النيتريك) مضاءة بعدة ألوان Deutsch: Chemikalienflaschen (inklusive Ammoniak und Salpetersäure), in verschiedenen Farben beleuchtet English: Chemicals in flasks (including Ammonium hydroxide and Nitric acid) lit in different colours فارسی: ترکیبات شیمیایی در داخل ظرف شیشه‌ای (شامل هیدروکسید آمونیوم و اسید نیتریک) نورپردازی شده در رنگ‌های مختلف 한국어: 여러 색으로 빛나는 플라스크들에 담겨져 있는 화학 물질들 (수산화암모늄, 질산 포함)Flasks
context_page_description: Chemistry is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.
  In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant chemistry, the formation of igneous rocks, how atmospheric ozone is formed and how environmental pollutants are degraded, the properties of the soil on the moon, how medications work, and how to collect DNA evidence at a crime scene.
  Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron; ionic bonds, in which a compound donates one or more electrons to another compound to produce ions; hydrogen bonds; and Van der Waals force bonds.
context_section_description: The current model of atomic structure is the quantum mechanical model. Traditional chemistry starts with the study of elementary particles, atoms, molecules, substances, metals, crystals and other aggregates of matter. Matter can be studied in solid, liquid, gas and plasma states, in isolation or in combination. The interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory.
  The chemistry laboratory stereotypically uses various forms of laboratory glassware. However glassware is not central to chemistry, and a great deal of experimental (as well as applied/industrial) chemistry is done without it.
  A chemical reaction is a transformation of some substances into one or more different substances. The basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal. (When the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay.) The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
  Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure, phase, as well as their chemical compositions. They can be analyzed using the tools of chemical analysis, e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists. Most chemists specialize in one or more sub-disciplines. Several concepts are essential for the study of chemistry; some of them are:
caption: Solutions of substances in reagent bottles, including ammonium hydroxide and nitric acid, illuminated in different colors
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