Chemistry
From Wikipedia, the free encyclopedia.
Chemistry is the scientific study of the structure, properties, composition, and reactions of chemical elements and compounds.
Overview
The atomic theory is basic to chemistry. The theory states that all matter is composed of a set of very small units called atoms. One of the very first laws to be discovered leading to the establishment of chemistry as a science is the Law of Conservation of Mass. This law states there is no detectable change in the quantity of matter during an ordinary chemical reaction. (Modern physics now shows that it is actually energy that is conserved, and that energy and mass are related) On a superficial level this means that if we start off with 10,000 atoms and proceed with many chemical reactions, we will still be left with exactly 10,000 atoms. The mass will be the same too if the energy gained or lost is accounted for. Chemistry studies the interactions of these atoms, sometimes alone but more often combined with (bonded to) other atoms to form ions and compounds/molecules. These atoms interact with other atoms (e.g., a wood fire is the combination of oxygen atoms from the air with the carbon and hydrogen atoms in the wood) and they may also interact with light (a photograph is formed from the changes that light causes to the chemicals on a film) and other types of radiation.
One surprisingly early finding was that these atoms almost always combine in definite ratios or proportions: silica sand is a structure where the ratio of silicon atoms to oxygen atoms is 1:2. We now know that there are exceptions to this law of definite proportions (integrated circuits are a good example).
Another key discovery in chemistry was that when a specific chemical reaction occurs, the amount of energy gained or lost will always be the same. This leads to the important concepts of equilibrium, thermodynamics, and kinetics.
Physical chemistry is grounded upon modern physics, and it is in principle possible to describe all chemical systems using the theory of quantum mechanics. This theory is mathematically complex and profoundly non-intuitive. In practice, however, only the simplest chemical systems may realistically be investigated in purely quantum mechanical terms, and approximations must be made for most practical purposes (e.g. Density functional theory). Hence a detailed understanding of quantum mechanics is not necessary for most chemistry, as the important implications of the theory (principally the orbital approximation) can be understood and applied in simpler terms.
Although quantum mechanics may frequently be ignored, the fundamental concept behind it - quantisation of energy - may not. Chemists depend on quantum effects for - amongst other things - all spectroscopic techniques, although many may not realise it! Again, frequently the physics may be ignored, and the end result (e.g. an NMR Spectrum) interpreted nonetheless.
A full physical description of chemistry must also take into account relativity, the other principle theory of modern physics, also mathematically complex. Fortunately, relativistic effects are only important in extremely precise calculations of atomic structure, mainly involving the heavier elements, and relativity is in practice irrelevant to almost all chemistry.
Branches of chemistry
Chemistry typically is divided into following major parts:
- Analytical chemistry, the determination of substance composition and its constituents;
- Organic chemistry, the study of carbon compounds;
- Inorganic chemistry, dealing with broader elements not emphasized in organic chemistry;
- Biochemistry, the study of chemistry in biological systems;
- Physical chemistry, which forms the foundation of all other branches, encompassing the physical property of substances and the theoretical tools to investigate them.
- Materials science
- Polymer chemistry
- Environmental chemistry
- Pharmacy
Chemicals and interactions
- Products and Reactants
- Systematic names
- Chemical formula
- Chemical bonding
- Chemical polarity
- Chemical equation
- Chemical reaction
- Colors of chemicals
Quantitative chemistry
States of matter
- Kinetic theory of gases
- Ideal gas
- Condensed matter physics
- Solutions
- Concentration of solutions
- Colligative properties
- Chemical equilibrium
- Le Chatelier's Principle
- Solubility
- Precipitates
- Common-ion effect
Acids and bases
- Acid-base reaction theories
- Strong acids
- Weak acids
- pH and the strength of acids
- Systematic naming of acids and bases
- Self-ionization of water
- Buffers
- Acid-Base titration
- Redox reactions
- Electrochemistry
Kinetics and thermodynamics
- Chemical kinetics
- Reaction rates
- Spontaneous processes
- Enthalpy
- Entropy
- Gibbs free energy
- Nuclear chemistry
- Biochemistry
History of chemistry
- Alchemy
- Discovery of the chemical elements
- Timeline of chemical element discovery
- Nobel Prize in chemistry
Etymology
Old French: alkemie; Arab al-kimia: the art of transformation.
See also
- List of chemistry topics
- Chemist and List of chemists
- American Chemical Society
- International Union of Pure and Applied Chemistry
- Chemical engineering
- Periodic table
- List of compounds
External links
- on
- IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms
- Material safety data sheets for a variety of chemicals
| Chemistry |
| Analytical chemistry | Organic chemistry | Inorganic chemistry | Biochemistry | Physical chemistry |
| Periodic table |