Dangling bond
Encyclopedia
In chemistry
, a dangling bond is an unsatisfied valence
on an immobilised atom
.
In order to gain enough electrons to fill their valence shells (see also octet rule
), many atoms will form covalent bond
s with other atoms. In the simplest case, that of a single bond, two atoms each contribute one unpaired electron, and the resulting pair of electrons is shared between both atoms. Atoms which possess too few bonding partners to satisfy their valences and which possess unpaired electrons are termed free radicals; so, often, are molecules containing such atoms. When a free radical exists in an immobilized environment, for example, a solid, it is referred to as an "immobilized free radical" or a "dangling bond".
Free and immobilized radicals display very different chemical characteristics from atoms and molecules containing only complete bonds. Generally, they are extremely reactive. Immobilized free radicals, like their mobile counterparts, are highly unstable, but gain some kinetic stability because of limited mobility and steric hindrance. While free radicals are usually short lived, immobilized free radicals often exhibit a longer lifetime because of this reduction in reactivity.
Some allotropes
of silicon, such as amorphous silicon
, display a high concentration of dangling bonds. Besides being of fundamental interest, these dangling bonds are important in modern semiconductor device
operation. Hydrogen introduced to the silicon during the synthesis process is well known to replace dangling bonds, as are other elements such as oxygen.
In computational chemistry
, a dangling bond is an error
in structure creation, in which an atom is inadvertently drawn with too few bonding partners, or a bond is mistakenly drawn with an atom at only one end.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, a dangling bond is an unsatisfied valence
Valence (chemistry)
In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...
on an immobilised atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
.
In order to gain enough electrons to fill their valence shells (see also octet rule
Octet rule
The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low (The octet rule is a chemical rule of thumb that states that atoms of low (...
), many atoms will form covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
s with other atoms. In the simplest case, that of a single bond, two atoms each contribute one unpaired electron, and the resulting pair of electrons is shared between both atoms. Atoms which possess too few bonding partners to satisfy their valences and which possess unpaired electrons are termed free radicals; so, often, are molecules containing such atoms. When a free radical exists in an immobilized environment, for example, a solid, it is referred to as an "immobilized free radical" or a "dangling bond".
Free and immobilized radicals display very different chemical characteristics from atoms and molecules containing only complete bonds. Generally, they are extremely reactive. Immobilized free radicals, like their mobile counterparts, are highly unstable, but gain some kinetic stability because of limited mobility and steric hindrance. While free radicals are usually short lived, immobilized free radicals often exhibit a longer lifetime because of this reduction in reactivity.
Some allotropes
Allotropy
Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, known as allotropes of these elements...
of silicon, such as amorphous silicon
Amorphous silicon
Amorphous silicon is the non-crystalline allotropic form of silicon. It can be deposited in thin films at low temperatures onto a variety of substrates, offering some unique capabilities for a variety of electronics.-Description:...
, display a high concentration of dangling bonds. Besides being of fundamental interest, these dangling bonds are important in modern semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
operation. Hydrogen introduced to the silicon during the synthesis process is well known to replace dangling bonds, as are other elements such as oxygen.
In computational chemistry
Computational chemistry
Computational chemistry is a branch of chemistry that uses principles of computer science to assist in solving chemical problems. It uses the results of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids...
, a dangling bond is an error
Error
The word error entails different meanings and usages relative to how it is conceptually applied. The concrete meaning of the Latin word "error" is "wandering" or "straying". Unlike an illusion, an error or a mistake can sometimes be dispelled through knowledge...
in structure creation, in which an atom is inadvertently drawn with too few bonding partners, or a bond is mistakenly drawn with an atom at only one end.