2. Anatomy & Physiology – Chemical Bonding Chemical Bonding

3. Anatomy & Physiology – Chemical Bonding ObjectivesObjectives Recognize that chemical reactions involve the interaction of electrons.Recognize that chemical reactions involve the interaction of electrons. Differentiate between ionic, covalent, and hydrogen bonds.Differentiate between ionic, covalent, and hydrogen bonds. Contrast synthesis, decomposition, and exchange reactions.Contrast synthesis, decomposition, and exchange reactions. At the end of this section you should be able to:

4. Anatomy & Physiology – Chemical Bonding Chemical Bonds and Chemical Reactions Chemical reactions occur whenever atoms combine with, or dissociate from, other atoms.Chemical reactions occur whenever atoms combine with, or dissociate from, other atoms. When atoms unite chemically, chemical bonds are formed.When atoms unite chemically, chemical bonds are formed.

5. Anatomy & Physiology – Chemical Bonding Bond Formation A chemical bond is not an actual physical structure, like a pair of handcuffs linking two people together.A chemical bond is not an actual physical structure, like a pair of handcuffs linking two people together. It is an energy relationship that involves interactions between the electrons of the reacting atoms.It is an energy relationship that involves interactions between the electrons of the reacting atoms.

6. Anatomy & Physiology – Chemical Bonding Role of Electrons Electrons occupy generally fixed regions of space around the nucleus.Electrons occupy generally fixed regions of space around the nucleus. These regions are called energy levels or electron shells.These regions are called energy levels or electron shells. The maximum number of energy levels in any atom known so far is 7, and these are numbered 1 to 7 from the nucleus outward.The maximum number of energy levels in any atom known so far is 7, and these are numbered 1 to 7 from the nucleus outward.

7. Anatomy & Physiology – Chemical Bonding The electrons closest to the nucleus are those most strongly attracted to its positive charge, and those farther away are less securely held.The electrons closest to the nucleus are those most strongly attracted to its positive charge, and those farther away are less securely held. As a result, the more distant electrons are likely to interact with other atoms.As a result, the more distant electrons are likely to interact with other atoms. There is an upper limit to the number of electrons that each electron shell can hold.There is an upper limit to the number of electrons that each electron shell can hold. Role of Electrons

8. Anatomy & Physiology – Chemical Bonding Energy Levels Shell 1, closest to the nucleus, is small and can accommodate only 2 electrons.Shell 1, closest to the nucleus, is small and can accommodate only 2 electrons. Shell 2 holds a maximum of 8.Shell 2 holds a maximum of 8. Shell 3 can accommodate up to 18 electrons.Shell 3 can accommodate up to 18 electrons. Subsequent shells hold larger and larger numbers of electrons.Subsequent shells hold larger and larger numbers of electrons.

9. Anatomy & Physiology – Chemical Bonding Energy Levels The only electrons that are important when considering bonding are those in the atom's outermost shell.The only electrons that are important when considering bonding are those in the atom's outermost shell. This shell is called the valence shell, and its electrons determine the chemical behavior of the atom.This shell is called the valence shell, and its electrons determine the chemical behavior of the atom. As a general rule, the electrons of inner shells do not take part in bonding.As a general rule, the electrons of inner shells do not take part in bonding.

10. Anatomy & Physiology – Chemical Bonding Energy Levels When the valence shell of an atom contains 8 electrons, the atom is completely stable and is chemically inactive.When the valence shell of an atom contains 8 electrons, the atom is completely stable and is chemically inactive. When the valence shell contains fewer than 8 electrons, an atom will tend to gain, lose, or share electrons with other atoms to reach the stable state.When the valence shell contains fewer than 8 electrons, an atom will tend to gain, lose, or share electrons with other atoms to reach the stable state.

11. Anatomy & Physiology – Chemical Bonding Types of Chemical Bonds

12. Anatomy & Physiology – Chemical Bonding Ionic Bonds Ionic bonds form when electrons are completely transferred from one atom to another.Ionic bonds form when electrons are completely transferred from one atom to another. Atoms are electrically neutral.Atoms are electrically neutral. When they gain or lose electrons during bonding, their positive and negative charges are no longer balanced, and charged particles, called ions, result.When they gain or lose electrons during bonding, their positive and negative charges are no longer balanced, and charged particles, called ions, result.

13. Ionic Bonds

14. Anatomy & Physiology – Chemical Bonding When an atom gains an electron, it acquires a net negative charge because it now has more electrons than protons.When an atom gains an electron, it acquires a net negative charge because it now has more electrons than protons. Negatively charged ions are called anions.Negatively charged ions are called anions. When an atom loses an electron, it becomes a positively charged ion because it now possesses more protons than electrons.When an atom loses an electron, it becomes a positively charged ion because it now possesses more protons than electrons. Positively charged ions are called cations.Positively charged ions are called cations. Ionic Bonds

15. Anatomy & Physiology – Chemical Bonding Covalent Bonds Electrons do not have to be completely lost or gained for atoms to become stable.Electrons do not have to be completely lost or gained for atoms to become stable. Electrons can be shared in such a way that each atom is able to fill its valence shell at least part of the time.Electrons can be shared in such a way that each atom is able to fill its valence shell at least part of the time. Molecules in which atoms share electrons are called covalent molecules, and their bonds are covalent bonds.Molecules in which atoms share electrons are called covalent molecules, and their bonds are covalent bonds.

16. Anatomy & Physiology – Chemical Bonding Because the shared electrons orbit and "belong to" the whole molecule, each atom has a full valence shell enough of the time to satisfy its stability needs.Because the shared electrons orbit and "belong to" the whole molecule, each atom has a full valence shell enough of the time to satisfy its stability needs. Electrons that are shared equally between the atoms of the molecule are called non-polar covalently bonded molecules.Electrons that are shared equally between the atoms of the molecule are called non-polar covalently bonded molecules. Covalent Bonds

18. Anatomy & Physiology – Chemical Bonding Hydrogen Bonds Hydrogen bonds are extremely weak bonds formed when a hydrogen atom bound to one electron ‑ hungry nitrogen or oxygen atom is attracted by another electron ‑ hungry atom, and the hydrogen atom forms a "bridge" between them.

19. Anatomy & Physiology – Chemical Bonding Chemical Reactions Chemical reactions involve interactions between atoms and molecules that involve the formation or breaking of chemical bonds.Chemical reactions involve interactions between atoms and molecules that involve the formation or breaking of chemical bonds. Three basic types of chemical reactions are:Three basic types of chemical reactions are: –Synthesis reactions –Decomposition reactions –Exchange reactions

20. Anatomy & Physiology – Chemical Bonding Synthesis Reactions In synthesis reactions, two or more substances called reactants combine to form a different more complex substance called a product.In synthesis reactions, two or more substances called reactants combine to form a different more complex substance called a product. Synthesis reactions result in the formation of new bonds, and energy is required for the reaction to occur and the new product to form.Synthesis reactions result in the formation of new bonds, and energy is required for the reaction to occur and the new product to form. The ability of the body to synthesize new tissue in wound repair is a good example of this type of reaction.The ability of the body to synthesize new tissue in wound repair is a good example of this type of reaction. Example: 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2Example: 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

21. Anatomy & Physiology – Chemical Bonding Decomposition Reactions Decomposition reactions result in breakdown of a complex substance into two or more simpler substances.Decomposition reactions result in breakdown of a complex substance into two or more simpler substances. In this type of reaction, chemical bonds are broken and energy is released.In this type of reaction, chemical bonds are broken and energy is released. Energy can be released in the form of heat, or it can be captured for storage and future use.Energy can be released in the form of heat, or it can be captured for storage and future use. Decomposition reactions occur when a complex nutrient is broken down in a cell to release energy for other cellular functions.Decomposition reactions occur when a complex nutrient is broken down in a cell to release energy for other cellular functions.

22. Anatomy & Physiology – Chemical Bonding Decomposition Reactions Example: NaCl Na + + Cl -Example: NaCl Na + + Cl - The products of such a reaction are ultimately waste products.The products of such a reaction are ultimately waste products. Decomposition and synthesis are opposites.Decomposition and synthesis are opposites.

23. Anatomy & Physiology – Chemical Bonding Exchange Reactions The nature of exchange reactions permits two different reactants to exchange components and form two new products.The nature of exchange reactions permits two different reactants to exchange components and form two new products. Exchange reactions break down or decompose two compounds and, in exchange, synthesize two new compounds.Exchange reactions break down or decompose two compounds and, in exchange, synthesize two new compounds. Certain exchange reactions take place in the blood.Certain exchange reactions take place in the blood. Example: HCl + NaOH NaCl + H 2 OExample: HCl + NaOH NaCl + H 2 O

24. Anatomy & Physiology – Chemical Bonding Chemical Composition of Living Matter All chemicals found in the body fall into one of two major classes of molecules; they are either organic or inorganic compounds.All chemicals found in the body fall into one of two major classes of molecules; they are either organic or inorganic compounds. The class of the compound is determined by the presence or absence of carbon.The class of the compound is determined by the presence or absence of carbon. Organic compounds are carbon ‑ containing compounds.Organic compounds are carbon ‑ containing compounds.

25. Anatomy & Physiology – Chemical Bonding BiochemistryBiochemistry The important organic compounds in the body are carbohydrates, lipids, proteins, and nucleic acids.The important organic compounds in the body are carbohydrates, lipids, proteins, and nucleic acids. All organic compounds are fairly large covalently bonded molecules.All organic compounds are fairly large covalently bonded molecules. With a few exceptions inorganic compounds lack carbon and tend to be simpler, smaller molecules.With a few exceptions inorganic compounds lack carbon and tend to be simpler, smaller molecules.