anatomy & physiology – chemical bonding chemical bonding

Anatomy & Physiology – Chemical BondingAnatomy & Physiology – Chemical Bonding

Chemical BondingChemical BondingChemical BondingChemical Bonding


ObjectivesObjectivesObjectivesObjectives

• Recognize that chemical reactions involve the Recognize that chemical reactions involve the interaction of electrons.interaction of electrons.

• Differentiate between ionic, covalent, and Differentiate between ionic, covalent, and hydrogen bonds.hydrogen bonds.

• Contrast synthesis, decomposition, and Contrast synthesis, decomposition, and exchange reactions.exchange reactions.

At the end of this section you should At the end of this section you should be able to:be able to:


Chemical Bonds and Chemical Bonds and Chemical ReactionsChemical ReactionsChemical Bonds and Chemical Bonds and Chemical ReactionsChemical Reactions

• Chemical reactions occur whenever atoms combine Chemical reactions occur whenever atoms combine with, or dissociate from, other atomswith, or dissociate from, other atoms. .

• When atoms unite chemically, chemical bonds are When atoms unite chemically, chemical bonds are formedformed..


Bond FormationBond FormationBond FormationBond Formation

• A chemical bond is not an actual physical structure, A chemical bond is not an actual physical structure, like a pair of handcuffs linking two people together. like a pair of handcuffs linking two people together.

• It is an energy relationship that involves It is an energy relationship that involves interactions between the electrons of the reacting interactions between the electrons of the reacting atoms. atoms.


Role of ElectronsRole of ElectronsRole of ElectronsRole of Electrons

• Electrons occupy generally fixed regions of space Electrons occupy generally fixed regions of space around the nucleusaround the nucleus..

• These regions are called energy levels or electron These regions are called energy levels or electron shellsshells. .

• The maximum number of energy levels in any The maximum number of energy levels in any atom known so far is 7atom known so far is 7, and these are numbered 1 , and these are numbered 1 to 7 from the nucleus outward.to 7 from the nucleus outward.


• The electrons closest to the The electrons closest to the nucleus are those most nucleus are those most strongly attracted to its strongly attracted to its positive chargepositive charge, and those , and those farther away are less farther away are less securely held. securely held.

• As a result, the more As a result, the more distant electrons are likely distant electrons are likely to interact with other to interact with other atoms.atoms.

• There is an upper limit to There is an upper limit to the number of electrons the number of electrons that each electron shell can that each electron shell can holdhold..

Role of ElectronsRole of ElectronsRole of ElectronsRole of Electrons


Energy Levels Energy Levels Energy Levels Energy Levels

• Shell 1, closest to the Shell 1, closest to the nucleus, is small and can nucleus, is small and can accommodate only 2 accommodate only 2 electronselectrons..

• Shell 2 holds a maximum of Shell 2 holds a maximum of 88. .

• Shell 3 can accommodate Shell 3 can accommodate up to 18 electronsup to 18 electrons. .

• Subsequent shells hold Subsequent shells hold larger and larger numbers larger and larger numbers of electrons.of electrons.


Energy LevelsEnergy LevelsEnergy LevelsEnergy Levels

• The only electrons that are important when The only electrons that are important when considering bonding are those in the atom's considering bonding are those in the atom's outermost shelloutermost shell. .

• This shell is called the valence shell, and its This shell is called the valence shell, and its electrons determine the chemical behavior electrons determine the chemical behavior of the atomof the atom. .

• As a general rule, the electrons of inner As a general rule, the electrons of inner shells do not take part in bonding.shells do not take part in bonding.


Energy LevelsEnergy LevelsEnergy LevelsEnergy Levels

• When the valence shell of an atom contains When the valence shell of an atom contains 8 electrons, the atom is completely stable 8 electrons, the atom is completely stable and is chemically inactiveand is chemically inactive. .

• When the valence shell contains fewer than When the valence shell contains fewer than 8 electrons, an atom will tend to gain, lose, 8 electrons, an atom will tend to gain, lose, or share electrons with other atoms to or share electrons with other atoms to reach the stable statereach the stable state. .


Types of Chemical BondsTypes of Chemical BondsTypes of Chemical BondsTypes of Chemical Bonds


Ionic Bonds Ionic Bonds Ionic Bonds Ionic Bonds

• Ionic bonds form when electrons are Ionic bonds form when electrons are completely transferred from one atom to completely transferred from one atom to anotheranother. .

• Atoms are electrically neutral.Atoms are electrically neutral.

• When they gain or lose electrons during When they gain or lose electrons during bonding, their positive and negative bonding, their positive and negative charges are no longer balanced, and charges are no longer balanced, and charged particles, called ions, resultcharged particles, called ions, result..


• When an atom gains an electron, it acquires When an atom gains an electron, it acquires a net negative chargea net negative charge because it now has because it now has more electrons than protons. more electrons than protons.

• Negatively charged ions are called anionsNegatively charged ions are called anions. .

• When an atom loses an electron, it When an atom loses an electron, it becomes a positively chargedbecomes a positively charged ion because it ion because it now possesses more protons than electrons.now possesses more protons than electrons.

• Positively charged ions are called cationsPositively charged ions are called cations..



Covalent BondsCovalent BondsCovalent BondsCovalent Bonds

• Electrons do not have to be completely lost Electrons do not have to be completely lost or gained for atoms to become stable. or gained for atoms to become stable.

• Electrons can be shared in such a way that Electrons can be shared in such a way that each atom is able to fill its valence shell at each atom is able to fill its valence shell at least part of the time.least part of the time.

• Molecules in which atoms share electrons Molecules in which atoms share electrons are called covalent molecules, and their are called covalent molecules, and their bonds are covalent bondsbonds are covalent bonds..


• Because the shared electrons orbit and Because the shared electrons orbit and "belong to" the whole molecule, each atom "belong to" the whole molecule, each atom has a full valence shell enough of the time has a full valence shell enough of the time to satisfy its stability needs.to satisfy its stability needs.

• Electrons that are shared equally between Electrons that are shared equally between the atoms of the molecule are called non-the atoms of the molecule are called non-polar covalently bonded moleculespolar covalently bonded molecules. .



Hydrogen BondsHydrogen BondsHydrogen BondsHydrogen Bonds

Hydrogen bonds are Hydrogen bonds are extremely weak extremely weak

bonds formed when a bonds formed when a hydrogen atom bound hydrogen atom bound

to one to one electronelectron‑‑hungry hungry

nitrogen or oxygen nitrogen or oxygen atom is attracted by atom is attracted by

another another electronelectron‑‑hungry atom, hungry atom,

and the hydrogen and the hydrogen atom forms a "bridge" atom forms a "bridge"

between thembetween them..


Chemical ReactionsChemical ReactionsChemical ReactionsChemical Reactions

• Chemical reactions involve interactions Chemical reactions involve interactions between atoms and molecules that involve between atoms and molecules that involve the formation or breaking of chemical the formation or breaking of chemical bondsbonds. .

• Three basic types of chemical reactions are:Three basic types of chemical reactions are:– Synthesis reactionsSynthesis reactions

– Decomposition reactions Decomposition reactions

– Exchange reactionsExchange reactions


Synthesis ReactionsSynthesis ReactionsSynthesis ReactionsSynthesis Reactions

• In synthesis reactions, two or more substances In synthesis reactions, two or more substances called reactants combine to form a different called reactants combine to form a different more complex substance called a productmore complex substance called a product. .

• Synthesis reactions result in the formation of Synthesis reactions result in the formation of new bonds, and energy is requirednew bonds, and energy is required for the for the reaction to occur and the new product to form. reaction to occur and the new product to form.

• The ability of the body to synthesize new The ability of the body to synthesize new tissue in wound repair is a good example of tissue in wound repair is a good example of this type of reaction.this type of reaction.

• Example: 6COExample: 6CO22 + 6H + 6H22O CO C66HH1212OO66 + + 6O6O22


Decomposition ReactionsDecomposition ReactionsDecomposition ReactionsDecomposition Reactions

• Decomposition reactions result in breakdown Decomposition reactions result in breakdown of a complex substance into two or more of a complex substance into two or more simpler substancessimpler substances. .

• In this type of reaction, chemical bonds are In this type of reaction, chemical bonds are broken and energy is releasedbroken and energy is released. .

• Energy can be released in the form of heat, or Energy can be released in the form of heat, or it can be captured for storage and future use.it can be captured for storage and future use.

• Decomposition reactions occur when a Decomposition reactions occur when a complex nutrient is broken down in a cell to complex nutrient is broken down in a cell to release energy for other cellular functions.release energy for other cellular functions.


Decomposition ReactionsDecomposition ReactionsDecomposition ReactionsDecomposition Reactions

• Example: NaCl NaExample: NaCl Na++ + Cl + Cl--

• The products of such a reaction are The products of such a reaction are ultimately waste products. ultimately waste products.

• Decomposition and synthesis are opposites.Decomposition and synthesis are opposites.


Exchange Reactions Exchange Reactions Exchange Reactions Exchange Reactions

• The nature of exchange reactions permits The nature of exchange reactions permits two different reactants to exchange two different reactants to exchange components and form two new productscomponents and form two new products. .

• Exchange reactions break down or Exchange reactions break down or decompose two compounds and, in decompose two compounds and, in exchange, synthesize two new compoundsexchange, synthesize two new compounds. .

• Certain exchange reactions take place in Certain exchange reactions take place in the blood.the blood.

• Example: HCl + NaOH NaCl + HExample: HCl + NaOH NaCl + H22OO


Chemical Composition of Living Chemical Composition of Living MatterMatter

Chemical Composition of Living Chemical Composition of Living MatterMatter

• All chemicals found in the body fall into one All chemicals found in the body fall into one of two major classes of molecules; they are of two major classes of molecules; they are either organic or inorganic compoundseither organic or inorganic compounds. .

• The class of the compound is determined by The class of the compound is determined by the presence or absence of carbonthe presence or absence of carbon. .

• Organic compounds are carbonOrganic compounds are carbon‑‑containing containing compoundscompounds..


BiochemistryBiochemistryBiochemistryBiochemistry

• The important organic compounds in the The important organic compounds in the body are carbohydrates, lipids, proteins, body are carbohydrates, lipids, proteins, and nucleic acidsand nucleic acids. .

• All organic compounds are fairly large All organic compounds are fairly large covalently bonded molecules. covalently bonded molecules.

• With a few exceptions inorganic compounds With a few exceptions inorganic compounds lack carbon and tend to be simpler, smaller lack carbon and tend to be simpler, smaller moleculesmolecules..

anatomy & physiology – chemical bonding chemical bonding

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