bond

The formation of a covalent bond between two hydrogen atoms to form a hydrogen molecule (H₂), and between two hydrogen atoms and an oxygen atom to form a molecule of water (H₂O). The sharing means that each atom has a more stable arrangement of electrons (its outer electron shells are full).

In chemistry, the result of the forces of attraction that hold together atoms in an element or compound. The principal types of bonding are ionic, covalent, metallic, and intermolecular (such as hydrogen bonding).

The type of bond formed depends on the elements concerned and their electronic structure. In an ionic or electrovalent bond, common in inorganic compounds, the combining atoms gain or lose electrons to become ions; for example, sodium (Na) loses an electron to form a sodium ion (Na⁺) while chlorine (Cl) gains an electron to form a chloride ion (Cl⁻) in the ionic bond of sodium chloride (NaCl).

In a covalent bond, the atomic orbitals of two atoms overlap to form a molecular orbital containing two electrons, which are thus effectively shared between the two atoms. Covalent bonds are common in organic compounds, such as the four carbon–hydrogen bonds in methane (CH₄). In a dative covalent or coordinate bond, one of the combining atoms supplies both of the valence electrons in the bond.

A metallic bond joins metals in a crystal lattice, the atoms occupy lattice positions as positive ions, and valence electrons are shared between all the ions in an ‘electron gas’.

In a hydrogen bond, a hydrogen atom joined to an electronegative atom, such as nitrogen or oxygen, becomes partially positively charged, and is weakly attracted to another electronegative atom on the same or a neighbouring molecule.

The strongest known noncovalent bond is the superbond that is formed between avidin, a protein found in egg white, and the growth factor biotin. It is almost impossible to separate the two molecules once bonded. The superbond is used in a number of biomedical research applications.

bond

In commerce, an interest-bearing security issued by a government, local authority, company, bank, or other institution. Usually a lower-risk, long-term security, a bond may be irredeemable (with no date of redemption), secured (giving the investor a claim on the company's property or on a part of its assets), or unsecured (not protected by a lien). Bonds are generally issued for a fixed period, at a fixed (nominal) value, are repayable on a fixed date (the maturity date), and pay a fixed rate of interest (although they can carry a floating rate) during that period. Property bonds are non-fixed securities with the yield fixed to property investment. Bonds are bought and sold in a similar way to equities and are an alternative way for the issuer to raise capital. Financial institutions often consider the prevailing interest rates when setting the price of bonds in an attempt to make them attractive to purchasers. See also Eurobond.