What is Chemistry ?
Definition of Chemistry:
Chemistry is the science of matter (that is, of all physical substances including gases and liquids as well as solids) and the changes that occur between different kinds of matter - especially chemical changes (called "reactions") when types of matter are re-arranged into other types of matter e.g. water splitting into the gases hydrogen and oxygen.
That is, chemistry is a physical science concerned with the composition, structure, behaviour, and properties of matter and with the changes it undergoes during, and as a result of, chemical reactions. It involves study of substances in all of the the states of matter (solid, liquid and gas) and knowledge and understanding of the various structures of matter (incl. e.g. atoms, molecules, crystals and other aggregates) whether in isolation or in combination with others.
Major Branches of Chemistry
Chemistry is a huge subject within which there are several "branches", i.e. topics or areas of study that are distinctive, recognised, parts of the overall subject of chemistry. It is not possible to answer the question What is Chemistry ? without reference to particular types of chemistry.
Introductory (school-level) chemistry cannot include all branches of chemistry, some of which are highly specialised. However, even at secondary school level students aged 14-16 may study chemistry in terms of the three main categories of Physical Chemistry, Inorganic Chemistry and Organic Chemistry. Examples of topics included in each of these areas are listed below.
Other Branches of Chemistry
Other, in many cases highly specialised, disciplines within chemistry are also important and are often named according to the context or manner in which understanding of matter is important. Examples include:
- Agrochemistry (also called "Agricultural chemistry") - the study of chemistry for agricultural production, food processing, etc..
- Analytical chemistry - analysis of physical samples to understand their chemical composition and structure.
- Astrochemistry - study of the existence and reactions of matter in the wider universe beyond planet earth.
- Atmospheric chemistry - the chemistry of the Earth's atmosphere and that of other planets.
- Biochemistry - the study of substances found in ,or produced by, biological organisms.
- Cosmochemistry - study of the origin and development of the substances of the universe (not just Earth).
- Electrochemistry - the chemistry of reactions in solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte).
- Environmental chemistry - study of biochemical phenomena occurring in natural locations.
- Femtochemistry - study of chemical reactions over very short times-frames, approx. 10-15 seconds (one femtosecond), hence the name.
- Geochemistry - chemical composition of the Earth and other planets, chemical processes and reactions determining composition of rocks and soils, and cycles of matter/energy that transport matter and their interaction with the hydrosphere and atmosphere.
- Immunochemistry - study of the chemistry and reactions affecting the immune system, hence related to medicine and veterinary science.
- Marine chemistry (also called "Ocean chemistry" - study of chemistry of marine environments incl. e.g. PH levels, atmospheric chemistry, chemistry affecting local ecology, etc.
- Mathematical chemistry - applications of mathematics to chemistry, e.g. involving mathematical modeling of chemical behaviours.
- Medicinal chemistry (also called "pharmaceutical chemistry") - at the intersection of chemistry and pharmacology incl. designing, synthesising and developing pharmaceutical drugs.
- Neurochemistry - study of neurochemicals, incl. neurotransmitters and neuro-active drugs that influence neuron function.
- Nuclear Chemistry - aspects of chemistry concerning radioactivity, nuclear processes and nuclear properties.
- Organometallic chemistry - study of chemicals containing bonds between carbon and a metal (incl. aspects of inorganic chemistry and organic chemistry).
- Petrochemistry - study of the transformation of crude oil (petroleum) and natural gas into useful products and raw materials for other products.
- Photochemistry - study of chemical reactions that involve absorption of light e.g. degradation of certain materials
- Phytochemistry - study of chemicals derived from plants ("phytochemicals") and the secondary metabolic compounds found in plants.
- Polymer chemistry - study of organic macromolecules whose structure generally includes long chains of carbon atoms, can include bio- or synthetic polymers.
- Radiochemistry - study of radioactive substances and use of radioactivity to study chemical reactions generally.
- Solid-state chemistry (also called "Materials chemistry") - the study of the synthesis, structure, and properties of solids, especially but not only, non-molecular solids. This is related to solid-state physics, mineralogy, crystallography,etc..
- Sonochemistry - study of chemical effects of sonic waves / ultrasound, generally arising from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid.
- Supramolecular chemistry, - study of weak and reversible non-covalent interactions between molecules, e.g. hydrogen bonds, metal coordination, hydrophobic forces, van der Waals forces, pi-pi interactions, electrostatic effects.
- Surface chemistry - chemical reactions at interfaces, this overlaps with electrochemistry.
- Synthetic chemistry - application of knowledge of matter to deliberately produce specific substances artificially (as opposed to naturally).
- Theoretical Chemistry - the application of of physics (and sometimes also mathematical techniques) to explain or predict chemical phenomena.
- Thermochemistry - study of the energy evolved or absorbed in chemical reactions and physical transformations, such as melting and boiling.
The specialties mentioned above do not form a complete list but help to convey a broad impression of What is Chemistry?
In some cases there are many more sub-specialties within these areas. The above gives a general impression of the wide scope of chemistry and the contexts in which it is important.
Comparison with other Science subjects:
Comparison between Chemistry and Physics
Some aspects of the structure and behaviour of matter are also described by the associated science of physics, but with different emphasis: Chemistry is concerned with the composition, structure, behaviour, and properties of matter, and with the changes it undergoes during and as a result of chemical reactions. Physics is generally more concerned with the observable or measurable effects of changes in or to bulk materials, e.g. as described by the Laws of Motion, Law of Gravity, electricity, magnetism, optics, etc..
Chemistry and physics interface and even overlap in some areas of study, e.g. concerning sub-atomic particles, radiation, and aspects of atmospheric and environmental research. Chemistry makes use of aspects of physics in areas of physical chemistry and contributes to physics in many ways, e.g. re. various types of protective coatings for surfaces and concerning colour, such as for optical components and filters, coatings, etc..
Comparison between Chemistry and Biology
Biology is the physical (including chemical) study of life and living things.
It includes human biology (which is associated with medicine and its specialties), zoology (i.e. animal life, associated subjects being veterinary science and its specialties) and botany (concerning plant life). It is described here as a "physical" study of "life" to distinguish it from disciplines interested in life from other perspectives, such as anthropology, sociology, philosophy, ethics, and the many religious and other (less structured/hierarchical, but also) "spiritual" approaches to the concept of life and experience of it.
In common with biology, chemistry attempts to describe and explain matter, living or otherwise, in terms of its composition, structure, properties, and so on. Aspects of the structure and behaviour of living matter and matter formed by living organisms are also described by the associated science of biology, hence the interface and overlap between chemistry and biology, which is called biochemistry. Biochemistry is not usually offered as a separate subject in its own right at introductory level, such as in schools and colleges. This is because it is necessary to have a good basic understanding of both biology and chemistry in order to understand some of the more advanced issues at the interface of the two subjects. Another discipline that uses knowledge of both introductory chemistry and biology is microbiology.
A good understanding of at least introductory chemistry is extremely useful for appreciating advanced biology generally because (in physical terms), all living things ultimately consist of the atoms and molecules described and explained by courses in school-level chemistry and beyond. Conversely, knowledge of biology is not essential for appreciation of all areas of advanced chemistry. For example, industrial processes e.g. in the automotive and plastics industries, require advanced chemistry for applications unrelated to living organisms. However, even then, some understanding of biology may be useful e.g. for health and safety issues or for responsible sourcing of raw materials.