Chemistry
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:
Other cross-disciplinary studies and specialization branches include:
Chemicals and interactions
Quantitative chemistry
States of matter
Acids and bases
Kinetics and thermodynamics
History of chemistry
Etymology
Old French: alkemie; Arab al-kimia: the art of transformation.See also
External links
| Chemistry |
| Analytical chemistry | Organic chemistry | Inorganic chemistry | Biochemistry | Physical chemistry |
| Periodic table |