radical

radical, in chemistry

radical, in chemistry, group of atoms that are joined together in some particular spatial structure and that take part in most chemical reactions as a single unit. Important inorganic radicals include ammonium, NH₄; carbonate, CO₃ ; chlorate, ClO₃, and perchlorate, ClO₄ ; cyanide, CN; hydroxide, OH; nitrate, NO₃; phosphate, PO₄; silicate, SiO₃ (meta) or SiO₄ (ortho); and sulfate, SO₄. The use of these radicals simplifies the naming and description of inorganic compounds, since such usage does not consider the electronic charge on the group. (When ions are dealt with, electronic charge must be considered.) In organic chemistry, the term radical is sometimes used synonymously with group; e.g., the group CH₃ is sometimes called the methyl radical instead of the methyl group. This use is limited chiefly to alkyl groups and aryl groups; it is usually not applied to functional groups, such as carbonyl. Because the term radical easily could be taken to mean a free radical, the term group is preferred by some.

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radical, in mathematics

radical, in mathematics, symbol placed over a number or expression, called the radicand, to indicate a root of the radicand. When used without a sign or index number, it designates the positive square root of the radicand, i.e., 2. If both square roots are meant, the radical sign is preceded by ±. To indicate higher roots of the radicand, e.g., cube or fourth roots, an index number is used. The radical sign is generally taken to indicate the principal root of the radicand, although any radicand will have n different nth roots. The term radical is sometimes used loosely to refer to the entire expression consisting of radical sign and radicand.

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radical

Term used in chemistry with one predominant and two subsidiary, looser meanings. It most often refers to a free radical. It can also mean an ion or a functional group.

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radical

In politics, one who desires extreme change of part or all of the social order. The term (which derives from the Latin word for “root,” and thus implies change beginning at a system's roots) was given this sense by Charles James Fox in 1797 when he demanded “radical reform” consisting of universal manhood suffrage. In France before 1848, republicans and advocates of universal male suffrage were called radicals. The term was later applied to Marxists (see Marxism) who called for fundamental social change to eradicate divisions among social classes. In popular usage, it is applied to political extremism, not necessarily violent, of both the left and the right.

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radical

1. favouring or tending to produce extreme or fundamental changes in political, economic, or social conditions, institutions, habits of mind, etc

2. Med (of treatment) aimed at removing the source of a disease

3. of, relating to, or arising from the root or the base of the stem of a plant

4. Maths of, relating to, or containing roots of numbers or quantities

5. a person who favours extreme or fundamental change in existing institutions or in political, social, or economic conditions

6. Maths a root of a number or quantity, such as ³&#221A5, &#221Ax

7. Chem

a. short for free radical

b. another name for group