metallic bond: see chemical bond; metal.

junk bond, a bond that involves greater than usual risk as an investment and pays a relatively high rate of interest, typically issued by a company lacking an established earnings history or having a questionable credit history. Junk bonds became a common means for raising business capital in the 1980s, when they were used to help finance the purchase of companies, especially by leveraged buyouts; the sale of junk bonds continued to be used in the 1990s to generate capital. See also Milken, Michael.

ionic bond: see chemical bond.

electrovalent bond: see chemical bond.

covalent bond: see chemical bond.

chemical bond, mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as an independent species. The number of bonds an atom forms corresponds to its valence. The amount of energy required to break a bond and produce neutral atoms is called the bond energy. All bonds arise from the attraction of unlike charges according to Coulomb's law; however, depending on the atoms involved, this force manifests itself in quite different ways. The principal types of chemical bond are the ionic, covalent, metallic, and hydrogen bonds. The ionic and covalent bonds are idealized cases, however; most bonds are of an intermediate type.

The Ionic Bond

The ionic bond results from the attraction of oppositely charged ions. The atoms of metallic elements, e.g., those of sodium, lose their outer electrons easily, while the atoms of nonmetals, e.g., those of chlorine, tend to gain electrons. The highly stable ions that result retain their individual structures as they approach one another to form a stable molecule or crystal. In an ionic crystal like sodium chloride, no discrete diatomic molecules exist; rather, the crystal is composed of independent Na⁺ and Cl^- ions, each of which is attracted to neighboring ions of the opposite charge. Thus the entire crystal is a single giant molecule.

The Covalent Bond

A single covalent bond is created when two atoms share a pair of electrons. There is no net charge on either atom; the attractive force is produced by interaction of the electron pair with the nuclei of both atoms. If the atoms share more than two electrons, double and triple bonds are formed, because each shared pair produces its own bond. By sharing their electrons, both atoms are able to achieve a highly stable electron configuration corresponding to that of an inert gas. For example, in methane (CH₄), carbon shares an electron pair with each hydrogen atom; the total number of electrons shared by carbon is eight, which corresponds to the number of electrons in the outer shell of neon; each hydrogen shares two electrons, which corresponds to the electron configuration of helium.

In most covalent bonds, each atom contributes one electron to the shared pair. In certain cases, however, both electrons come from the same atom. As a result, the bond has a partly ionic character and is called a coordinate link. Actually, the only purely covalent bond is that between two identical atoms.

Covalent bonds are of particular importance in organic chemistry because of the ability of the carbon atom to form four covalent bonds. These bonds are oriented in definite directions in space, giving rise to the complex geometry of organic molecules. If all four bonds are single, as in methane, the shape of the molecule is that of a tetrahedron. The importance of shared electron pairs was first realized by the American chemist G. N. Lewis (1916), who pointed out that very few stable molecules exist in which the total number of electrons is odd. His octet rule allows chemists to predict the most probable bond structure and charge distribution for molecules and ions. With the advent of quantum mechanics, it was realized that the electrons in a shared pair must have opposite spin, as required by the Pauli exclusion principle. The molecular orbital theory was developed to predict the exact distribution of the electron density in various molecular structures. The American chemist Linus Pauling introduced the concept of resonance to explain how stability is achieved when more than one reasonable molecular structure is possible: the actual molecule is a coherent mixture of the two structures.

Metallic and Hydrogen Bonds

Unlike the ionic and covalent bonds, which are found in a great variety of molecules, the metallic and hydrogen bonds are highly specialized. The metallic bond is responsible for the crystalline structure of pure metals. This bond cannot be ionic because all the atoms are identical, nor can it be covalent, in the ordinary sense, because there are too few valence electrons to be shared in pairs among neighboring atoms. Instead, the valence electrons are shared collectively by all the atoms in the crystal. The electrons behave like a free gas moving within the lattice of fixed, positive ionic cores. The extreme mobility of the electrons in a metal explains its high thermal and electrical conductivity.

Hydrogen bonding is a strong electrostatic attraction between two independent polar molecules, i.e., molecules in which the charges are unevenly distributed, usually containing nitrogen, oxygen, or fluorine. These elements have strong electron-attracting power, and the hydrogen atom serves as a bridge between them. The hydrogen bond, which plays an important role in molecular biology, is much weaker than the ionic or covalent bonds. It is responsible for the structure of ice.

bond, chemical: see chemical bond.

bond, in finance, usually a formal certificate of indebtedness issued in writing by governments or business corporations in return for loans. It bears interest and promises to pay a certain sum of money to the holder after a definite period, usually 10 to 20 years. Security is usually pledged against a bond; unsecured bonds are regarded as a long-term obligation on the capital of the issuing body. Some bonds are convertible upon maturity into the stock of the issuing company. One method used to retire bonds is the sinking fund; in such a case the issuing body buys back some of its bonds each year and holds them itself, applying the interest to the fund. The entire bond issue, most of which the firm has already acquired, is then retired on maturity. In the case of serial bonds, part of the issue is called in and paid for in full each year. Bonds were sold by the U.S. government to finance both World Wars and are still an important money-raising device. Government bonds are backed by the full faith and credit of the government issuing them, including its taxing power, and sometimes also by specifically designated security. Bonds are usually bought by those wishing conservative investment. A junk bond has a risky credit rating because it is issued by companies without an established earnings history or with a questionable credit history. Junk bonds have increasingly been used to help finance the purchase of companies, especially in leveraged buyouts.

Stockdale, James Bond, 1923-2005, U.S. naval officer, b. Abingdon, Ill.; grad. U.S. Naval Academy, 1947. A fighter pilot and highly decorated career naval officer (1946-79), he was the highest ranking U.S. prisoner of war (1965-73) in North Vietnam during the Vietnam War. He rose to the rank of vice admiral before retiring from the navy and was president of the Naval War College (1976-79) and of The Citadel (1979-80). From 1981 to 1996 he was a senior research fellow at the Hoover Institution on War, Revolution, and Peace. He wrote A Vietnam Experience (1985) and several other books. Stockdale was H. Ross Perot's vice presidential running mate in 1992.

Head, Sir Francis Bond, 1793-1875, British administrator in Canada. A soldier (1811-25) and unsuccessful mining adventurer in South America, he had had little experience to prepare him for the post of lieutenant governor of Upper Canada (Ontario), to which he was appointed in 1835. Sir Francis's reactionary policy in Canada and his alliance with the Family Compact estranged Robert Baldwin and the moderate reformers and drove William Lyon Mackenzie and other radical reformers into open rebellion in 1837. Head, who had resigned but had not yet been replaced in his post, quelled this uprising. He left Canada in 1838, never again to hold public office, and devoted his later years to writing.

Bond, William Cranch, 1789-1859, American astronomer, b. Portland, Maine. He early aided his father in the trades of silversmith and clockmaker in Boston. He soon became an expert in the making of chronometers and by 1812 was fashioning most of the superior ones used by ships sailing out of Boston. He developed a passion for astronomy, and, turning part of his home into an amateur observatory, he devoted all his free time to it. In 1815 he was sent by Harvard College to Europe to visit existing observatories and gather data preliminary to the building of an observatory at Harvard. In 1839 the observatory was founded; Bond supervised its construction and became its first director. In 1847 a 15-in. (37.5 cm) telescope, then matched in size by only one other in the world, was installed. With it, Bond made elaborate studies of sunspots, of the Orion nebula, and of the planet Saturn, publishing his results chiefly in the Annals of the Harvard College Observatory. Together with his son he developed the chronograph for automatically recording the position of stars, and he was a pioneer in the use of the chronometer and the telegraph for determining longitude. He and his son George Phillips Bond made the first practical use in America of Daguerre's photographic process applied to astronomy.

Bond, Sir Robert, 1857-1927, Newfoundland political leader. He was educated in England and later entered Newfoundland politics. In 1890, he negotiated a reciprocity agreement between Newfoundland and the United States, but protests from the rest of Canada prevented its ratification. After he became prime minister in 1900, he repurchased the railways and docks from private interests. His ministry was marked by attempts to diversify Newfoundland's economy away from fishing and by disputes over U.S. fishing in provincial waters. Bond's government fell in 1909, and his influence quickly declined. He was knighted in 1901.

Bond, Julian (Horace Julian Bond), 1940-, U.S. civil-rights leader, b. Nashville, Tenn. As a student at Morehouse College, he participated in sit-ins at segregated Atlanta restaurants. He was a founder (1960) of the Student Nonviolent Coordinating Committee, serving (1961-65) as its communications director. Elected (1965) to the Georgia assembly, Bond was denied his seat because of his statements opposing the war in Vietnam. Reelected in 1966, he began serving after the U.S. Supreme Court upheld (Dec., 1966) his right to hold office. A state representative until 1974, he then served as a state senator (1975-87). Bond led a group of black delegates to the 1968 Democratic Convention where he challenged the party's unit rule and won representation at the expense of the regular Georgia delegation. In 1986 he lost a Georgia congressional race to John Lewis. In 1998 he became chairman of the National Association for the Advancement of Colored People. He is the author of A Time to Speak, a Time to Act (1972).

Bond, George Phillips, 1825-65, American astronomer, b. near Boston, grad. Harvard, 1845. He became the assistant of his father, William Cranch Bond, and in 1859 succeeded him as director of the Harvard College Observatory. Much of his work was done in cooperation with his father. While they were studying Saturn together, George, in 1848, discovered its eighth satellite, Hyperion (which was independently discovered in that same year by the English astronomer William Lassell). His observations led him to reject the previously held theory that the rings of Saturn were of solid structure, though his hypothesis of their being in fluid state was in turn soon discarded. His memoir on the Donati comet of 1858 in the Annals of the Harvard College Observatory, Vol. III, remains one of the most complete descriptions of a great comet that has been written. His revision of his father's work on the Orion nebula was published posthumously. His photographs of the moon created a sensation among astronomers in Europe when taken there in 1851. He was a pioneer in the use of photography in mapping the sky, determining stellar parallax, and measuring double stars. He also used photographs for determining the comparative brightness of the planets.

Bond, Carrie Jacobs, 1862-1946, American songwriter, b. Janesville, Wis. A self-taught musician, she composed about 175 songs, both words and music, gave concerts of them, and even published them herself. Eventually the popularity of such songs as I Love You Truly, Just a-Wearyin' for You, and A Perfect Day earned her a fortune.

Bond Street, in Westminster, London, England, famous for its fashionable shops. Among the noted residents of Bond St. have been the authors Laurence Sterne, James Boswell, and Jonathan Swift; Admiral Horatio Nelson; and Lady Emma Hamilton.

or limited obligation bond

Bond issued by a municipality, state, or public agency authorized to build, acquire, or improve a revenue-producing property such as a waterworks, electric generating plant, or railroad. Unlike general-obligation bonds, which are repaid through a variety of tax sources, revenue bonds are payable from specified revenues only, usually the revenues from the facility for which the bond was originally issued. Revenue bonds typically pay interest rates higher than those of general-obligation bonds. The separation of the revenue bond obligation from a municipality's other bond obligations allows the municipality to circumvent legislated debt limits.

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Electrostatic attraction between oppositely charged ions in a chemical compound. Such a bond forms when one or more electrons are transferred from one neutral atom (typically a metal, which becomes a cation) to another (typically a nonmetallic element or group, which becomes an anion). The two types of ion are held together by electrostatic forces in a solid that does not comprise neutral molecules as such; rather, each ion has neighbours of the opposite charge in an ordered overall crystalline structure. When, for example, crystals of common salt (sodium chloride, NaCl) are dissolved in water, they dissociate (see dissociation) into two kinds of ions in equal numbers, sodium cations (Na⁺) and chloride anions (Cl⁻). Seealso bonding; covalent bond.

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Force holding atoms in a molecule together as a specific, separate entity (as opposed to, e.g., colloidal aggregates; see bonding). In covalent bonds, two atoms share one or more pairs of valence electrons to give each atom the stability found in a noble gas. In single bonds (e.g., HsinglehorzbondH in molecular hydrogen), one electron pair is shared; in double bonds (e.g., OdoublehorzbondO in molecular oxygen or H₂CdoublehorzbondCH₂ in ethylene), two; in triple bonds (e.g., HCtriplehorzbondCH in acetylene), three. In coordinate covalent bonds, additional electron pairs are shared with another atom, usually forming a functional group, such as sulfate (SO₄) or phosphate (PO₄). The number of bonds and the atoms participating in each (including any additional paired electrons) give molecules their configuration; the slight negative and positive charges at the opposite ends of a covalent bond are the reason most molecules have some polarity (see electrophile; nucleophile). Carbon in organic compounds can have as many as four single bonds, each pointing to one vertex of a tetrahedron; as a result, certain molecules exist in mirror-image forms (see optical activity). Double bonds are rigid, leading to the possibility of geometric isomers (see isomerism). Some types of bonds, such as the amide linkages that join the amino acids in peptides and proteins (peptide bonds), are apparently single but have some double-bond characteristics because of the electronic structure of the participating atoms. The configurations of enzymes and their substrates, determined by their covalent bonds (particularly the peptide bonds) and hydrogen bonds, are crucial to the reactions they participate in, which are fundamental to all life. Seealso aromatic compound; compare ionic bond.

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Any of the interactions that account for the association of atoms into molecules, ions, crystals, metals, and other stable species. When atoms' nuclei and electrons interact, they tend to distribute themselves so that the total energy is lowest; if the energy of a group arrangement is lower than the sum of the components' energies, they bond. The physics and mathematics of bonding were developed as part of quantum mechanics. The number of bonds an atom can form—its valence—equals the number of electrons it contributes or receives. Covalent bonds form molecules; atoms bond to specific other atoms by sharing an electron pair between them. If the sharing is even, the molecule is not polar; if it is uneven, the molecule is an electric dipole. Ionic bonds are the extreme of uneven sharing; certain atoms give up electrons, becoming cations. Other atoms take up the electrons and become anions. All the ions are held together in a crystal by electrostatic forces. In crystalline metals, a diffuse electron sharing bonds the atoms (metallic bonding). Other types include hydrogen bonding; bonds in aromatic compounds; coordinate covalent bonds; multicentre bonds, exemplified by boranes (boron hydrides), in which more than two atoms share electron pairs; and the bonds in coordination complexes (see transition element), still poorly understood. Seealso van der Waals forces.

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In finance, loan contract issued by local, state, and national governments and by private corporations, specifying an obligation to return borrowed funds. The issuer promises to pay interest on the debt when due (usually semiannually) at a stipulated percentage of the face value and to redeem the face value of the bond at maturity in legal tender. Bonds usually indicate a debt of substantial size and are issued in more formal fashion than promissory notes, ordinarily under seal. Government bonds may be backed by taxes, or they may be revenue bonds, backed only by revenue from the specific project (toll roads, airports, etc.) to which they are committed. Bonds are rated based on the issuer's creditworthiness. The ratings, assigned by independent rating agencies, generally run from AAA to D; bonds with ratings from AAA to BBB are regarded as suitable for investment. Seealso junk bond.

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Temporary release of a prisoner in exchange for security given to guarantee the prisoner's appearance at a later hearing. It also refers to the actual security given (e.g., cash). Its main use today is to secure the freedom, pending trial, of someone arrested and charged with a criminal offense. Its use in civil (noncriminal) cases is far less common, as most do not involve imprisonment. The amount of bail is generally set in relation to the gravity of the offense, though other factors, such as the strength of the evidence, the character of the accused, and the accused's ability to secure bail may also be considered. Seealso bond, recognizance.

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(born Jan. 14, 1940, Nashville, Tenn., U.S.) U.S. politician and civil-rights leader. The son of prominent educators, Bond graduated from Morehouse College. In 1960 he helped create the Student Nonviolent Coordinating Committee (SNCC). In 1965 he was elected to the Georgia legislature, but his support of a SNCC statement accusing the U.S. of violating international law in the Vietnam War caused the legislature to deny him his seat. He was twice reelected and was twice more refused entry. The U.S. Supreme Court ruled his exclusion unconstitutional in December 1966, and he assumed his seat in January 1967. He later served in the state senate (1975–87). In 1998 he became chairman of the NAACP.

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