Chemistry

Chemistry is the study of the atomic building blocks of nature, how they combine and their combinations which form the solids, liquids, and gases that make up most forms of matter. For the many different chemical elements and compounds, see:

The Periodic table
List of compounds
Inorganic chemistry, including solid state chemistry, which studies the basic principles that are applied in mineralogy and materials science.
Organic chemistry, which underlies biochemistry and polymer chemistry and is the study of carbon-containing molecules.
Physical chemistry, which includes computational chemistry, quantum chemistry and surface chemistry.
Analytical chemistry, the basis of environmental chemistry.
Photochemistry, which through photosynthesis drives all of life.

Basics

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 Matter. The law states there is no detectable change in the quantity of matter during an ordinary chemical reaction. (Modern Physics now teaches that atoms and energy can be neither created nor destroyed.) On a superficial level this means that if we start off with 10,001 atoms and proceed with many chemical reactions, we will be left with 10,001 atoms. Even if we started off with something green and gooey and ended up with something black and hard there will still be the same number of 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 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 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 change is made, the amount of energy gained or lost will always be the same. This leads to the important concepts of equilibrium, thermodynamics, and kinetics. The most interesting theory describing all of chemistry is Quantum Mechanics. This theory is complex, non-intuitive, and difficult to master. Often, simpler concepts are used to predict the results of experiments. These concepts (e.g. acid/base chemistry) are limited in scope, but much easier to understand and apply. College students typically study chemistry in the following "blocks": Analytical Chemistry, Physical Chemistry, Organic Chemistry, Inorganic Chemistry, Polymer Chemistry and Biochemistry. Often, discoveries in chemistry are made by physicists, biologists, chemical engineers or pharmacists.

Scientific method
SI base unit
Significant figures
The Atom
Orbitals
Periodic Table of Chemical elements
Isomerism
Allotropes
Isotopes
Ion
Electron configuration
Periodic Trends
Elemental Groups: S-block, D-block, F-block, P-block

Chemicals and Interactions

Quantitative Chemistry

States of Matter

Acids and Bases

Kinetics and Thermodynamics

History of Chemistry

External links

IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms
Material safety data sheets for a variety of chemicals