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Bonding

Bonding


In the everyday world around us, we observe three very different types of materials: gases, liquids, and solids. Closer examination of the physical properties of homogeneous crystalline solids shows that they can be subdivided into four distinct categories according to their physical properties and the different forces holding them together. For each category, we must develop a bonding picture, based on electrons, that will lead to an understanding of the physical properties exhibited. We can classify the solids according to the distribution of the valence electrons of the atoms (as shown in Figure 1), which explains their physical properties.

Types of Solids

Metallic. A metal is a substance that can conduct electricity both as a solid and when it is molten. The range of melting points for metals is very large, from 39°C for mercury to 1,083°C for copper and 3,200°C for tungsten. The outermost valence electrons of the atoms belong to the crystal as a whole, delocalized as a "sea" in which they are freely mobile to flow from atom to atom. The positive nuclei of the atoms are embedded in the sea as a close-packed three-dimensional array.

Ionic. Ionic materials are those that are brittle and that conduct electricity when molten but not as solids. Melting points range upwards from about 500°C. Examples are CaO (quicklime), MgF2, and NaCl (common table salt). The electrons are constrained about each atom, some atoms with excess positive charge (cations) and some with excess negative charge (anions). The ions are packed closely together, held by coulomb (electrostatic) forces of attraction.

Covalent network. A solid that is extremely hard, that has a very high melting point, and that will not conduct electricity either as a solid or when molten is held together by a continuous three-dimensional network of covalent bonds. Examples include diamond, quartz (SiO2), and silicon carbide (SiC). The electrons are constrained in pairs to a region on a line between the centers of pairs of atoms.

Van der Waals molecular. A material that has a very low melting point and that will not conduct electricity either as a solid or when molten consists of molecules that are close-packed, bump-in-hollow and that are attracted to each other by weak van der Waals attractions. Examples include carbon dioxide (CO2, dry ice), iodine (I2), and naphthalene (mothballs). The electrons are constrained to the well-defined groups of atoms that constitute the molecules. The atoms within the molecules are linked together by strong covalent bonds. The weak attractions between the molecules, termed London forces, arise from the charge asymmetry in the molecules that result from the polarizability of their electron clouds.

The Tetrahedron of Bonding Types

These four extreme types of bonding can be represented on the four apexes of a tetrahedron. (See Figure 2.)

The various intermediate types of bonding lie along the edges. Choosing examples that exemplify the extreme types of bonding is straightforward. It is far more difficult to identify appropriate solids to illustrate the six intermediate cases (those that lie along the edges of the tetrahedron), yet it is these very materials that are the most interesting and that often have important applications. The criteria for selecting them must include

  • Melting point;
  • Conductance as a solid;
  • Conductance when molten;
  • Pattern and number of close contacts in the solid; and
  • Atom-atom distances in the solid

because these are the properties that characterize the four extreme types of bonding.

Metallic Bonding

Metals are unique in that they can conduct electric current in the solid state. (Examples include aluminum high voltage transmission cables and copper

wire in domestic wiring.) Also, metals are ductile and malleable; they can be hammered into sheets, such as the pressed steel used as body parts for a car. The layers of atoms can slide past each other on a cushion of electrons, yet the solid remains whole. (See Figure 1.)

In many metals, each atom is in contact with twelve others: six in a plane, three above, and three below. These are termed close-packed hexagonal(e.g., magnesium), or face-centered cubic (e.g., copper). In other metals (e.g., iron), each atom is in contact with eight others at the corners of a cube; such structures are called body-centered cubic.

To a first approximation, we expect that the melting point of the metal should be related to the number of valence electrons that each atom contributes to the "sea." Two series of metals, as outlined in Table 1, illustrate the effect.

The simple model fits observation remarkably well for pure metals. However, this model begins to fail for alloys (solutions of one metal in another), such as brass and bronze, where for certain stoichiometries the material has anomalous physical properties and behaves almost as a compound(e.g., CuZn and Cu5Sn, termed Hume-Rothery electron phases).

MELTING POINTS OF METALS
Group in the
Periodic Table
1 2 3 4
Metal K Ca Sc Ti
Melting point (˚C) 64 850 1,539 1,875
Metal Rb Sr Y Zr
Melting point (˚C) 39 770 1,509 1,852
PROPERTIES OF IONIC COMPOUNDS
Compound q+ × q Lattice Energy
(kJ/mole)
Melting Point
(˚C)
Solubility
in Water
NaCl 1 × 1 = 1 770 808 Soluble
CaF2 2 × 1 = 2 2,610 1,418 Insoluble
MgO 2 × 2 = 4 3,906 3,070 Insoluble

Ionic Bonding

When two elements of very different groups in the Periodic Table react (e.g., the metals Na and Mg from Groups 1 and 2 on the left side with the nonmetals O2 and Cl2 from Groups 6 and 7 on the right side), the product is a solid (usually colorless) that has a high melting point. The product is an insulator but will conduct electricity in the molten state. The solid is built of alternating positively charged cations and negatively charged anions, packed tightly together, the exact pattern depending on the charges on the ions, q+ and q, and on their relative sizesthe radius ratio r+/r. In general, the metal atom loses electrons to leave a cation with a closed shellan octet, at the cost of the ionization energy (IE): Na° e Na+. A halogen atom will acquire an electron to form an anion with a closed shell, releasing energy, the electron affinity (EA): F + e F.

The attractive forces within the crystalline ionic structure are of the form M (q+ × q)/(r+ + r)2, where the value of M, the Madelung constant, depends on the pattern of packing of the ions. We can expect that the product (q+ × q) should give an indication of the cohesive energy of the solid. (See Table 2.)

A large value of the lattice energy indicates very strong bonding in the solid, hence a high melting point, and insolubility in water. The face-centered cubic structure adopted by the ionic compounds NaCl and MgO is shown in Figure 3. The small spheres represent the cations, and the large spheres represent the anions.

Covalent Bonding

This type of bonding is found between pairs of similar atoms, especially among those in the upper right hand corner of the periodic table. For example, CC in hydrocarbons, SO in sulfur dioxide, CF in Freons. The bonds can give rise to three-dimensional structures like diamond, and are found in simple molecules like H2S. These bonds are strong, and result in molecules with fixed geometry, such as methane, and give rise to optical activity in molecules such as lactic acid where the C atom is rigidly bonded to four different groups.

Pairs of electrons. Covalent bonding occurs between two atoms as a result of the sharing of a pair of electrons between the atoms. An example is provided in Figure 4.

Octets and Lewis Structures When bonded, atoms of the elements C, N, O, and F always tend to be associated with eight electrons in the valence shellthe "octet." The simultaneous attaining of a pair of electrons per covalent bond and an octet around the heavy atom is a powerful bookkeeping method of accounting for the bonding in molecules of the lighter main group elements in the periodic table. The diagrams are termed Lewis structures. The three-dimensional network structures are built around atoms with four bonds in a tetrahedron. For example, in diamond each carbon atom shares electrons with four neighbors to give four covalent bonds in a tetrahedral array. (See Figure 5.)

The diamond crystal can thus be imagined as a huge carbon molecule (Cx). If the pairs of electrons in the diagrams are replaced by lines to represent the covalent bonds, ammonia becomes

and methane becomes

Each straight line represents a localized two-center two-electron bond. In the ammonia molecule, one pair of electrons on the nitrogen atom is not involved in directly bonding to the H atoms; this is termed a lone pair. Unfortunately these Lewis diagrams can say nothing about the shape of the molecule. This comes much later by the Sidgwick-Powell/Gillespie/Nyholm-VSEPR approach to molecular geometry.

If we apply the Lewis formalism to the diatomic molecules of nitrogen, oxygen, and fluorine, we get

NN, a triple bond   O=O, a double bond   FF, a single bond

The three molecules obey the octet rule, and in each case all of the electrons are paired. The experimental facts show that for oxygen this bonding picture is wrong: Oxygen is paramagnetic; that is, the molecule has two unpaired electrons. This simplistic picture has failed, and a new approach to covalent bonding is required.

There are two other approaches to understanding covalent bonding: the molecular orbital (MO) theory and the valence bond (VB) theory. The VB approach is useful when considering molecular geometry. The MO approach is important when considering electronic spectra and other energy properties of the molecule. These topics are discussed separately.

Hybrid atomic orbitals and shapes of molecules. The valence electrons of the light elements lithium to fluorine are distributed in atomic orbitals 2s, 2px, 2py, and 2pz, whose shapes are given in Figure 6.

If they are close in energy, the s and p orbitals of an atom can interact to give combinations of different geometry, called hybrid atomic orbitals. This is nicely seen in the simple hydrocarbons, because the energy gap between the 2s and 2p orbitals in the carbon atom is relatively small, about 4 electron volts compared to 16 electron volts in the oxygen atom. The combination of one s plus three p orbitals gives four sp3 hybrid orbitals oriented in a tetrahedron, with an interorbital angle of 109½°. The combination of one s plus two p orbitals gives three sp2 hybrid orbitals arranged in a trigonal plane, with an interorbital angle of 120°. The combination one s plus one p orbital gives two collinear sp hybrid orbitals. (See Figure 7.)

The sp3 hybrids about the C atom are used to form the four bonds in diamond, methane, and all alkanes. The sp2 hybrids are used to form the double bond in all alkenes. The sp hybrids are used in the triple bond in acetylene. The shapes of the molecules of the simple gases ethane, ethylene, and acetylene are well described by the hybrid model. (See Table 3.)

PHYSICAL PROPERTIES OF THREE SIMPLE HYDROCARBONS
Ethane Ethylene Acetylene
Formula H3CCH3 H2C==CH2 HCCH
Molecular mass 30 28 26
Boiling point (˚C) 88.6 103.7 84.0
Shape 3H's, part of a tetrahedron about each C 4H's and 2C's coplanar, HCH angle = 120˚ H's and C's collinear
CC bond, orbitals Single, sigma Double, sigma + pi Triple, sigma + two pi

All three compounds burn in air. Acetylene is used for welding; ethylene is polymerized to give polyethylene, a plastic common in every kitchen.

Coordinate Bond

Molecules, such as ammonia, that have a lone pair of electrons are able to donate these two electrons to an empty orbital on a metal atom, to form a coordinate or dative bond. A typical example is the deep blue coordination complex of copper, [Cu(NH3)4]2+, which has four Cu(NH3) bonds in a square plane.

Similarly, a proton will attach itself to the lone pair of electrons on the ammonia molecule to give the tetrahedral NH4+ ammonium cation. The lone pair on the N atom in N(CH3)3 will bond to the empty orbital on the B atom in B(CH3)3 to give the compound (CH3)3NB(CH3)3.

The F anion will donate a pair of electrons to the B atom in the BF3 molecule to form the tetrahedral BF4 anion. This type of bonding where one atom, the donor, supplies both electrons to form the bond to the second atom, the acceptor, is termed Coordinate, or sometimes Dative.

Van der Waals Attractions

Materials held together by van der Waals attractions often have a smell at room temperature (e.g., camphor and menthol). This is caused by the molecules escaping from the solid and subliming directly into the gas phase . The attractive forces between the molecules are weak. These forces arise from distortions in the electron cloud around the molecule, which cause some parts to be relatively positively charged, while other parts are relatively negative.

Polar bonds. When a covalent (electron pair) bond is formed between two different atoms, the pair of electrons is concentrated nearer the atom with the larger power to attract electrons. This power is termed electronegativity. The charge asymmetry generates a bond moment. For example,

Depending on its shape, the molecule as a whole can have a dipole moment μ. For instance, for BF3, μ =0 because BF3 is trigonal planar, while for NF3, μ =0.23 D, because NF3 is pyramidal . The presence of a dipole moment in a molecule results in attractions between pairs of molecules, termed Keesom forces.

Polarizability. More interestingly, neutral molecules with a zero dipole moment are mutually attracted to give liquids (such as CCl4) and solids (such as naphthalene). These attractions, termed London forces or dispersion forces, arise from the ease of distortion of the electron cloud of the molecule as a whole. This is termed polarizability and is related to the volume of the molecule and the number of electrons in the valence shells of the atoms on the exposed surface of the molecule. The net effect (surprisingly, perhaps) is large and accounts for the relatively high melting points of iodine, CO2 (dry ice), and naphthalene. These London forces are important; they are the attractions between the long-chain polymeric molecules in solid polyvinyl chloride (PVC) and polyethylene.

Hydrogen bonding . The effect of polarity of a covalent bond is magnified in the case of a hydrogen atom bonded to an atom of either fluorine, oxygen, or nitrogen. In simple molecules, the distortion of the electron cloud is large, causing the hydrogen atoms to be slightly positively charged. For instance,

This results in a strong attraction between pairs of molecules:

These strong intermolecular attractions are termed hydrogen bonds and, unlike London forces, are directional. They would be represented in the cross-hatched area in Figure 2. It is this intermolecular hydrogen bonding that causes boiling points to be considerably higher than might be expected for molecules with low molecular masses, such as HF, H2O, and NH3. (See Table 4.)

PHYSICAL PROPERTIES OF SIMPLE COMPOUNDS
Compound CH4 NH3 H2O HF SiH4 PH3 H2S HCl
Molecular mass 16 17 18 20 32 34 34 36
Boiling Point (˚C) 161 33 +100 +20 111 88 60 85
μ(D) 0 1.46 1.84 1.82 0 0.58 0.97 1.08

Figure 8 compares the boiling points of the series CH4, SiH4, GeH4, and SnH4 with those of H2O, H2S, H2Se, H2Te, and the inert gases, and it shows the very high boiling point of water. It is these same OH···O hydrogen bonds

that hold water on a cotton facecloth and that are the forces between the base pairs in the DNA in our bodies.

Intermediate Cases

There are many homogeneous materials in which the bonding cannot be described simply as one of the four extreme types. The bonding in these materials is intermediate in character. For example, tin at room temperature is metallic in nature, but on cooling, it totally changes its electronic structure and adopts the diamond structure. A small change in energy nudges the tin atoms over the edge as the bonding teeters on the brink between metallic and covalent. It was this change that caused the tin buttons on the great coats of the soldiers of Napoleon's Grande Armée to crumble, during the terrible retreat from Moscow in the winter of 1812.

The element gallium is not truly metallic. In the solid, each gallium atom has one short bond of covalent character, and six other much longer contacts to neighboring atoms, intermediate in character between metallic and van der Waals, similar to the structure of crystalline iodine. The six intermediate types of bonding are not easy to describe, but in fact they are often the most important and certainly are very interesting.

Alloys. Many alloys have structures in which the atoms of the different metals are ordered. Hence they behave like compounds (e.g., AuCu3 and Cu5Zn8). CsAu has the NaCl structure (see Figure 3) and behaves almost as if it were ionic, Cs+ Au. This corresponds with the low ionization energy of Cs, 376 kilojoules per mole, and the favorable electron affinity of Au, 223 kilojoules per mole. CsAu's bonding would lie along the metal/ionic edge of the tetrahedron of bonding types.

Semiconductors. Semiconducting materials are of great practical importance in electronics. Ge, GaAs, ZnSe, and CuBr, are examples and they have bonding that can be described as intermediate between ideal covalent and ideal ionic. Each atom is bonded to four others in a tetrahedron, the zinc blende structure.

Silicate minerals. The bonding within a solid is always reflected in its physical properties, and this relationship to its internal structure is beautifully displayed in the morphology of the series of silicate minerals: quartz, mica, and asbestos. In quartz there is a three-dimensional network of SiO bonds. In mica there are negatively charged infinite sheets consisting of a two-dimensional network of SiO4 units, with the sheets linked by cations. In asbestos, there are infinite negatively charged chains of tetrahedral SiO4 units with strong covalent SiOSi bonds. The chains are attached to each other via cations. These latter two solids are each held together by two types of bonds, and the difference between the very strong covalent bonding and the other weaker attractions is evident. Mica is easily split into sheets, whereas asbestos consists of fibers.

Glass. Ordinary glass is an amorphous solid, constructed of negatively charged fragments of nets of SiO4 units that are linked by Na+ and Ca2+ cations. There is no internal order. As a result, glass shatters to give curved surfaces; and it gradually softens on heating and does not have a sharp melting point. The bonding in ceramic materials (such as bricks, tiles, pottery, and insulators) is similar, predominantly ionic.

Conclusion

It is important to remember that bonding is always accompanied by a reduction in energy, and that all bonding theory is but an intellectual model, a mental scaffolding on an atomic scale, on which to hang our ideas in hopes of giving a self-consistent explanation of observed reality.

see also Molecular Orbital Theory; Valence Bond Theory.

Michael Laing

Bibliography

Adams, D. M. (1974). Inorganic Solids. London: John Wiley & Sons.

Brady, James E.; Russell, Joel W.; and Holum, John R. (2000). Chemistry, 3rd edition. New York: John Wiley & Sons.

Brown, Theodore L.; Le May, H. Eugene; and Bursten, Bruce E. (2000). Chemistry, 8th edition. New Jersey: Prentice Hall.

de Kock, Roger L., and Gray, Harry B. (1980). Chemical Structure and Bonding. Menlo Park, CA: Benjamin/Cummings Publishing Co.

Huheey, James E.; Keiter, Ellen A.; and Keiter, Richard L. (1993). Inorganic Chemistry, 4th edition. New York: Harper Collins.

Ketelaar, J. A. A. (1958). Chemical Constitution, 2nd edition. Amsterdam, Netherlands: Elsevier.

Olmsted, John, and Williams, Gregory M. (2002). Chemistry, 3rd edition. New York: John Wiley & Sons.

Pauling, Linus (1960). The Nature of the Chemical Bond. Ithaca, NY: Cornell University Press.

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Bonding

Bonding

Definition

Bonding is the formation of a mutual emotional and psychological closeness between parents (or primary caregivers) and their newborn child. Babies usually bond with their parents in the minutes, hours, or days following birth.

Description

Bonding is essential for survival. The biological capacity to bond and form attachments is genetically determined. The drive to survive is basic in all species. Infants are defenseless and must depend on a caring adult for survival. The baby's primary dependence and the maternal response to this dependence causes bonding to develop.

Bonding and attachment are terms that describe the affectional relationships between parents and the infants. An increased awareness of the importance of bonding has led to significant improvements in routine birthing procedures and postpartum parent-infant contact. Bonding begins rapidly, shortly after birth, and reflects the feelings of parents toward the newborn; attachment involves reciprocal feelings between parent and infant and develops gradually over the first year. The focus of this entry is bonding in the newborn period. Attachment develops over the larger period of infancy and is treated in a separate entry.

Many parents, mothers in particular, begin bonding with their child before birth. The physical dependency the fetus has with the mother creates a basis for emotional and psychological bonding after birth. This attachment provides the foundation that allows babies to thrive in the world. When the umbilical cord is cut at birth, physical attachment to the mother ceases, and emotional and psychological bonding begins. A firm bond between mother and child affects all later development, and it influences how well children will react to new experiences, situations, and stresses.

Bonding research

American pediatricians John Kennell and Marshall Klaus pioneered scientific research on bonding in the 1970s. Working with infants in a neonatal intensive care unit, they noted that infants were taken away from their mothers immediately after birth for emergency medical procedures. These babies remained in the nursery for several weeks before being allowed to go home with their families. Although the babies did well in the hospital, a troubling percentage of them seemed not to prosper at home and were even victims of battering and abuse. Kennell and Klaus also noted the mothers of these babies were often uncomfortable with them, sometimes not believing that their babies had survived birth. Even mothers who had successfully raised previous infants have special difficulties when their children had been in the intensive care nursery. Kennell and Klaus surmised the separation immediately after birth interrupted a fundamental relationship between the mother and the new baby. They experimented with giving mothers of both premature and healthy full-term babies extra contact with their infants immediately after birth and in the few days following birth. Mothers with more access to their babies in the hospital developed better rapport with their infants, held them more comfortably, and smiled at and talked to them more often.

Gradually bonding research brought about widespread changes in hospital obstetrical practice in the United States. Fathers and family members often remain with the mother during labor and delivery. Mothers hold their infants immediately after birth, and babies often remain with their mothers throughout their hospital stay. Bonding research has also led to increased awareness of the natural capabilities of the infant at birth, and so it has encouraged many others to deliver their babies without anesthesia (which depresses mother and infant responsiveness).

Infancy

Emotionally and physically healthy mothers and fathers are attracted to their infant. They naturally feel a physical longing to smell, cuddle, and rock their infant. They look at their baby and communicate to the baby. In turn the infant responds with snuggling, babbling, smiling, sucking, and clinging. Usually, the parents' behaviors bring pleasure and nourishment to the infant, and the infant's behaviors bring pleasures and satisfaction to the parents. This reciprocal positive maternal and paternal-infant interaction initiates attachment.

One important part in the parents' ability to bond with the infant after birth is the healthy, drug-free newborn is in a "quiet alert" state for 45 to 60 minutes after birth. Immediately after birth the newborn can see, can hear, will turn his head toward a spoken voice, and will move in rhythm to his mother's voice. Mothers and fathers who have the opportunity to interact with their newborns within an hour after birth bond with their baby quickly. The act of holding, rocking, laughing, singing, feeding, gazing, kissing, and other nurturing behaviors involved in caring for infants (and young children) are bonding experiences. The most important ways to create attachment is positive physical contact such as hugging, holding, and rocking. It should be no surprise that nurturing behaviors cause specific neurochemical actions in the brain. These actions lead to organization of brain systems responsible for attachment.

Physical changes occur in the mother after birth, such as hormonal increases triggered by the infant licking or sucking her nipples and increased blood flow to her breasts when she hears the infant cry. Instinctive behaviors triggered in the mother in response to the infant immediately after birth promote her bonding with the infant and thus support the infant's survival.

Toddlerhood

Bonding experiences lead to healthy relations for children in the earliest years of life. During the first three years of life, the human brain develops to 90 percent of adult size. The brain puts in place most of the systems and structures that are responsible for future emotional, behavioral, social, and physiological functioning. Bonding experiences must be present at certain critical times for the brain parts responsible for attachment to develop normally. These critical periods appear in the first year of life and are related to the capacity of the infant and parent or caregiver to develop a positive interactive relation. Problems with bonding and attachment can lead to a fragile biological and emotional foundation for later experiences.

Common problems

Any problem with bonding experiences can interfere with attachment capacities. When the interactive, reciprocal "dance" between the parent and infant is disrupted or becomes difficult, bonding experiences are difficult to maintain. Disruptions can occur because of medical problems with the infant or the parent, the environment, or the fit between the infant and the parent.

The infant's personality or temperament influences bonding. If an infant is difficult to comfort, is irritable, or unresponsive, the baby may have more difficulty developing a secure bond. Moreover, the infant's ability to take part in the maternal-infant interaction may be compromised because of a medical condition, such as prematurity , birth defect, or illness.

The parent's or caregiver's behavior can also hinder bonding. Critical, rejecting, and interfering parents have children who may avoid emotional intimacy. Abusive parents have children who become uncomfortable with intimacy and withdraw. The child's mother may be unresponsive to the child because of maternal depression, substance abuse, or overwhelming personal problems that interfere with her ability to be consistent and nurturing for the child.

The environment is also a factor. A major impediment to healthy bonding is fear . If an infant is distressed because of pain , pervasive threat, or a chaotic environment, the baby may have a difficult time engaging in a sympathetic care-giving relationship. Infants or children living amid domestic violence, in refugee shelters, in areas besieged by community violence, or in war zones are at risk for developing attachment problems.

The fit between the infant's temperament and capabilities and those of the mother and father is important. Some parents can bond with a calm infant but are overwhelmed by an irritable infant. Understanding each other's nonverbal cues and responding appropriately is essential to preserving the bonding experiences that build healthy attachments. Sometimes a style of communication and response familiar to a mother from one of her other children may not fit her new infant. The mutual frustration of being "out of sync" can undermine bonding.

Since the first phase of bonding takes place in the womb, researchers believe difficult and unwanted pregnancies and planned adoptions interfere with mother and infant bonding. Teenagers and immature mothers often conceal and reject their pregnancies. This behavior and feeling may result in abandonment , neglect, and the absence of bonding at birth. Often there is also an emotional detachment from a fetus that causes emotional or physical pain to the mother during pregnancy. Mothers may have difficulty bonding with an infant if prenatal testing suggests the child will have a birth defect or is likely to be mentally retarded and malformed. And babies planned for adoption at birth may be "given up" emotionally by the birth mother during pregnancy. Any or all of these circumstances can interfere with the infant-parent bonding process.

Parental concerns

The birth of a premature infant is documented to be a time of stress and crisis for parents and infants. Among these stressors are perceived losses and grief from the early abrupt termination of pregnancy, feelings of guilt and failure in inability to carry the infant to term, uncertainty regarding the infant's future health and developmental potential, and immediate and long-term separation of the infant from the family.

Parental involvement in the care of sick or premature newborns is a major concern of many pediatricians and nursery staff. Touching, stroking, and talking, and, later, massaging are encouraged during frequent parental visits to the nursery. It is hoped that the emotional bonding of parents with low birth-weight infants will increase the baby's chance of doing well despite prematurity.

Because premature infants are sometimes seem fragile, parents may handle them less. Skin to skin contact is important to the growing infant, premature or full term. Lack of this contact may predispose the child to psychological problems as well as diminish opportunities for learning.

The practice of "kangaroo care," first introduced by two South American neonatologists, is a method of skin-to-skin contact to promote parent and infant bonding especially for premature infants. This method involves holding infants dressed only in a diaper and a hat between the mother's bare breasts or against the father's chest, similar to a kangaroo carrying their young. Through contact with their parents' skin, the babies are kept warm and allowed close interaction with their parents. This decreases some of the stressors associated with premature births and helps infants needing neonatal intensive care.

Parents who have experienced kangaroo care have expressed excitement and joy with the practice and many have felt like parents for the first time since their infant's birth. Infants have been observed in a restful sleep state while in the kangaroo position. As well, kangaroo care has been found to promote parent and infant bonding, breastfeeding, and early discharge for premature infants.

Kangaroo care is offered to stable babies who are less than 1,500 grams and are breathing on their own. Babies needing oxygen or nasal continuous positive airway pressure (CPAP) may also be eligible. Cardiopulmonary monitoring and oximetry may be continued during kangaroo care. The nurse remains nearby to monitor the infant as necessary.

KEY TERMS

Attachment A bond between an infant and a caregiver, usually its mother. Attachment is generally formed within the context of a family, providing the child with the necessary feelings of safety and nurturing at a time when the infant is growing and developing. This relationship between the infant and his caregiver serves as a model for all future relationships.

See also Attachment between infant and caregiver.

Resources

BOOKS

Rhatigan, Pamela. Soothe Your Baby the Natural Way: Bonding, Calming Rituals, Massage Techniques, Natural Remedies. London: Hamlyn, 2005.

WEB SITES

"Bonding Period." Birthing Naturally, October 2003. Available online at <www.birthingnaturally.net/barp/bonding.html> (accessed December 14, 2004).

Perry, Bruce D. "Bonding and Attachment in Maltreated Children: Consequences of Emotional Neglect in Childhood." Scholastic. Available online at <http://teacher.scholastic.com/professional/bruceperry/bonding.htm> (accessed December 14, 2004).

Aliene S. Linwood, RN, DPA, FACHE

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Bonding

Bonding

The process by which parents form a close personal relationship with their newborn child.

Bonding is the process by which parents form a close personal relationship with their newborn child. The term "bonding" is often used interchangeably with " attachment," a related phenomenon. For the purposes of this essay, bonding is confined to the newborn period. Attachment develops over the larger period of infancy and is treated in a separate entry.

The way parents feel about a new child is highly subjective and emotional, and can be very difficult to measure. Some researchers in the United States and elsewhere have attempted to show that there is a "sensitive period" soon after birth , in which the newborn is quietly alert and interested in engaging the mother, and the mother is able to attune to the new child. It is assumed, but not proven, that if mothers are given the opportunity to interact with their infants at this time, they are most likely to become bonded to the childto begin to respond to him, love him, and take care of him. Fathers who are with their partners at the birth also respond to the infant in characteristic ways immediately after birth.

American pediatricians John Kennell and Marshall Klaus pioneered scientific research on bonding in the 1970s. Working with infants in a neonatal intensive care unit, they often observed that infants were often taken away from their mothers immediately after birth for emergency medical procedures. These babies often remained in the nursery for several weeks before being allowed to go home with their families. Although the babies did well in the hospital, a troubling percentage of them seemed not to prosper at home, and were even victims of battering and abuse. Kennell and Klaus also noted that the mothers of these babies were often uncomfortable with them, and did not seem to believe that their babies had survived birth. Even mothers who had successfully raised previous infants seemed to have special difficulties with their children that had been treated in the intensive care nursery. Kennell and Klaus surmised that the separation immediately after birth interrupted some fundamental process between the mother and the new baby. They experimented with giving mothers of both premature and healthy full-term babies extra contact with their infants immediately after birth and in the few days following birth. Mothers who were allowed more access to their babies in the hospital seemed to develop better rapport with their infants, to hold them more comfortably, smile and talk to them more.

Studies conducted in the 1970s making these claims have come under attack in the 1980s and 1990s. Much of

the earlier research has been difficult to duplicate, and many mitigating factors in parent-child relationships make the lasting effects of early bonding experience difficult to pin down with scientific rigor. Nevertheless, bonding research brought about widespread changes in hospital obstetrical practice in the United States. Fathers and family members were allowed to remain with the mother during labor and delivery in many cases. Mothers were allowed to hold their infants immediately after birth, and in many cases babies remained with their mothers throughout their hospital stay. Bonding research has also led to increased awareness of the natural capabilities of the infant at birth, and so has encouraged many others to deliver their babies without anesthesia (which depresses mother and infant responsiveness).

One important factor in the parents' ability to bond with the infant after birth is that the healthy, undrugged newborn is often in what is called a "quiet alert" state for 45 to 60 minutes after birth. Research has demonstrated that immediately after birth the newborn can see and has visual preferences, can hear and will turn his head toward a spoken voice, and will move in rhythm to his mother's voice. Mothers and fathers allowed to interact with their newborns in this time frame often exhibit characteristic behaviors, such as stroking the baby, first with fingertips, then with the palm, looking in the baby's eyes, and speaking to the baby in a high-pitched voice. Researchers have also found physical changes in the mother right after birth, such as hormonal increases triggered by the infant licking or sucking her nipples, and increased blood flow to her breasts when hearing the infant cry. Some scientists speculate that there are instinctual behaviors triggered in the mother in response to the infant immediately after birth that facilitate her bonding with the infant, and thus promote the infant's survival.

Research on the bonding process has been scrutinized. Detractors call attention to the often poor research design of early studies and reject bonding as a scientific fallacy thrust on women to make them feel that they must react to their infants in certain prescribed fashions. Some people have misinterpreted bonding to mean that if the early sensitive period is missed, they cannot become successful parents. Obviously, parents can form close attachments to infants they did not see at birth, either because of medical emergencies or because their children are adopted. Thus, early experience with the newborn is only one factor in the complex relations of parents to children.

Despite some problems with quantifying bonding as a scientific phenomenon, there is a wealth of anecdotal evidence on the positive effects of an after-birth bonding experience. Most hospitals are now much more sensitive to parents' desire to be with their newborn than in the past. Parents-to-be may wish to find out their hospital's policies regarding the period immediately after birth. Questions to ask may include: Will the mother be allowed to hold the baby immediately if there is no problem? If tests are needed, can they be delayed until after the first hour? What family members can be present at the birth? Can family members be present at a cesarean birth? Will the baby stay in the same room with the mother or be sent to a central nursery? Some hospitals reportedly score mothers on how well they seem to bond with their infants, allegedly to flag potential future child abuse . This in effect makes early and rapid bonding a test, with failure potentially criminal, and egregiously violates the spirit of the hospital reform that bonding research brought about. If a hospital admits to "testing" for bonding, parents may ask if they may decline the test, or if they can have access to the test results. Ideally, both the birth and the period immediately after should be handled according to the parents' wishes.

A. Woodward

Further Reading

Eyer, Diane E. Mother-Infant Bonding: A Scientific Fiction. New Haven, CT: Yale University Press, 1992.

Gaskin, Ina May. Babies, Breastfeeding and Bonding. South Hadley, MA: Bergin & Garvey, 1987.

Klaus, Marshall H., John H. Kennell, and Phyllis H. Klaus. Bonding: Building the Foundations of Secure Attachment and Independence. Reading, MA: Addison-Wesley, 1995.

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bonding

bonding (bond-ing) n.
1. (in psychology) the development of a close and selective relationship, such as that of attachment.

2. (in dentistry) the attachment of dental restorations, sealants, and orthodontic brackets to teeth.

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bonding

bonding A term referring to the mutual identification of mother and child and the circumstances in which this develops. Sometimes it is used to describe the formation of other close relationships.

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bonding

bonding Social behaviour that tends to keep individuals together as cohesive groups (e.g. as herds, flocks, or schools), or as pairs (as in parent-infant or mating pairs).

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bonding

bonding Social behaviour that tends to keep individuals together as cohesive groups (e.g. as herds, flocks, or schools) or as pairs (as in parent-infant or mating pairs).

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bonding

bonding: see insurance.

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