Chapter 2

1. Chapter 2 The Chemical Level of Organization Lecture Outline

2. INTRODUCTION • Since chemicals compose your body and all body activities are chemical in nature, it is important to become familiar with the language and fundamental concepts of chemistry. Principles of Human Anatomy and Physiology, 11e

3. Chapter 2 The Chemical Level of Organization • Matter • elements • atoms and molecules • Chemical bonds • Chemical energy • Chemical reactions • Inorganic compounds • Organic compounds Principles of Human Anatomy and Physiology, 11e

4. Basic Principles • Chemistry is the science of the structure and interactions of matter. • Matter is anything that occupies space and has mass. • Mass is the amount of matter a substance contains • weight is the force of gravity acting on a mass. • Describe two ways that you could change your weight. Principles of Human Anatomy and Physiology, 11e

5. HOW MATTER IS ORGANIZED • Chemical Elements • All forms of matter are composed of chemical elements which are substances that cannot be split into simpler substances by ordinary chemical means. • Elements are given letter abbreviations called chemical symbols. • Oxygen (O), carbon (C), hydrogen (H), and nitrogen (N) make up 96% of body weight. • These elements, together with calcium (Ca) and phosphorus (P) make up 98.5% of total body weight. • Trace elements are present in tiny amounts • copper, tin, selenium & zinc Principles of Human Anatomy and Physiology, 11e

6. Review • Table 2.1 lists the major and trace elements of the human body. Principles of Human Anatomy and Physiology, 11e

7. Structure of Atoms • Units of matter of all chemical elements are called atoms. An element is a quantity of matter composed of atoms of the same type. • Atoms consist of a nucleus, which contains positively charged protons and neutral (uncharged) neutrons, and negatively charged electrons that move about the nucleus in energy levels (Figure 2.1). Principles of Human Anatomy and Physiology, 11e

8. Structure of Atoms • Atoms are the smallest units of matter that retain the properties of an element • 3 types of subatomic particles • protons, neutrons and electrons • Nucleus: protons (p+) & neutrons (neutral charge) • Electrons (e-) surround the nucleus as a cloud (electron shells are designated regions of the cloud) Principles of Human Anatomy and Physiology, 11e

9. Electron Shells • Most likely region of the electroncloud in which to find electrons • Each electron shell can hold onlya limited number of electrons • first shell can hold only 2 electrons • 2nd shell can hold 8 electrons • 3rd shell can hold 18 electrons • higher shells (up to 7) hold many more electrons • Number of electrons = number of protons • Each atom is electrically neutral; charge = 0 Principles of Human Anatomy and Physiology, 11e

10. Structure of Atoms • Electrons revolve around the nucleus of an atom tending to spend most of the time in specific atomic regions, called shells (Figure 2.1a). • Each shell can hold a certain maximum number of electrons. • The first shell, the one nearest the nucleus, can hold a maximum of 2 electrons; the second shell, 8; the third shell;18,the fourth shell, 18; and so on (Figure 2.1b). • The number of electrons in an atom of a neutral element always equals the number of protons. Principles of Human Anatomy and Physiology, 11e

11. Atomic Number and Mass Number • Atomic Number • The number of protons in the nucleus of an atom • The number of protons in the nucleus makes the atoms of one element different from those of another as illustrated in Figure 2.2. • Since all atoms are electrically neutral, the atomic number also equals the number of electrons in each atom. Principles of Human Anatomy and Physiology, 11e

12. Atomic Number & Mass Number • Atomic number is number of protons in the nucleus. . • Mass number is the sum of its protons and neutrons. Principles of Human Anatomy and Physiology, 11e

13. Atomic Number and Mass Number • The mass number of an atom is the sum of the numbers of protons and neutrons. • Different atoms of an element that have the same number of protons but different numbers of neutrons are called isotopes. • Isotopes • Stable isotopes do not change their nuclear structure over time. • Certain isotopes called radioactive isotopes are unstable because their nuclei decay to form a simpler and thus more stable configuration. • Radioactive isotopes can be used to study both the structure and function of particular tissues. Principles of Human Anatomy and Physiology, 11e

14. Atomic Mass • Mass is measured as dalton (atomic mass unit) • neutron has mass of 1.008 daltons • proton has mass of 1.007 daltons • electron has mass of 0.0005 dalton • Atomic mass (atomic weight) is close to the mass number of its most abundant isotope. Principles of Human Anatomy and Physiology, 11e

15. Atomic Number and Mass Number • Atomic Mass • The atomic mass, also called the atomic weight, of an element is the average mass of all its naturally occurring isotopes and reflects the relative abundance of isotopes with different mass numbers. • The mass of a single atom is slightly less than the sum of the masses of its neutrons, protons, and electrons because some mass (less than1%) was lost when the atom’s components came together to form an atom. Principles of Human Anatomy and Physiology, 11e

16. Ions, Molecules, & Compounds • Ions are formed by ionization • an atom that gave up or gained an electron • written with its chemical symbol and (+) or (-) • Molecule • atoms share electrons • written as molecular formula showing the number of atoms of each element (H2O) Principles of Human Anatomy and Physiology, 11e

17. Ions, Molecules, Free Radicals, and Compounds • If an atom either gives up or gains electrons, it becomes an ion - an atom that has a positive or negative charge due to having unequal numbers of protons and electrons. • When two or more atoms share electrons, the resulting combination is called a molecule (Figure 2.3a). Principles of Human Anatomy and Physiology, 11e

18. Free Radicals • A free radical is an electrically charged atom or group of atoms with an unpaired electron in its outermost shell (Figure 2.3b). • Unstable and highly reactive; can become stable • by giving up an electron • taking an electron from another molecule (example: breaking apart important body molecules) • Antioxidants are substances that inactivate oxygen-derived free radicals Principles of Human Anatomy and Physiology, 11e

19. Free Radicals & Your Health • Produced in your body by absorption of energy in ultraviolet light in sunlight, x-rays, by breakdown of harmful substances, & during normal metabolic reactions • Linked to many diseases -- cancer, diabetes, Alzheimer, atherosclerosis and arthritis • Damage may be slowed with antioxidants such as vitamins C and E, selenium & beta-carotene (precursor to vitamin A) Principles of Human Anatomy and Physiology, 11e

20. CHEMICAL BONDS • The atoms of a molecule are held together by forces of attraction called chemical bonds. • The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost shell, also called the valence shell. Principles of Human Anatomy and Physiology, 11e

21. CHEMICAL BONDS • An atom with a valence shell holding eight electrons (2 electrons for hydrogen and neon) is chemically stable, which means it is unlikely to form chemical bonds with other atoms. • To achieve stability, atoms that do not have eight electrons in their valence shell (or 2 in the case of H and He) tend to empty their valence shell or fill it to the maximum extent. • octet rule. • Atoms with incompletely filled outer shells tend to combine with each other in chemical reactions to produce a chemically stable arrangement of eight valence electrons for each atom. Principles of Human Anatomy and Physiology, 11e

22. Ionic Bonds • When an atom loses or gains a valence electron, ions are formed (Figure 2.4a). • Positively and negatively charged ions are attracted to one another. • Cations are positively charged ions that have given up one or more electrons (they are electron donors). • Anions are negatively charged ions that have picked up one or more electrons that another atom has lost (they are electron acceptors). Principles of Human Anatomy and Physiology, 11e

23. Ionic Bonds • When this force of attraction holds ions having opposite charges together, an ionic bond results. • Sodium chloride is formed by ionic bonds (Figure 2.4) • In general, ionic compounds exist as solids but some may dissociate into positive and negative ions in solution. Such a compound is called an electrolyte. • Table 2.2 lists the names and symbols of the most common ions and ionic compounds in the body. Principles of Human Anatomy and Physiology, 11e

24. The Ionic Bond in Sodium Chloride • Sodium loses an electron to become Na+ (cation) • Chlorine gains an electron to become Cl- (anion) • Na+ and Cl- are attracted to each other to form the compound sodium chloride (NaCl) -- table salt • Ionic compounds generally exist as solids Principles of Human Anatomy and Physiology, 11e

25. Covalent Bonds • Covalent bonds are formed by the atoms of molecules sharing one, two, or three pairs of their valence electrons. • Covalent bonds are common and are the strongest chemical bonds in the body. • Single, double, or triple covalent bonds are formed by sharing one,two, or three pairs of electrons, respectively (Figures 2.5a – d). • Covalent bonds may be nonpolar or polar. • In a nonpolar covalent bond, atoms share the electrons equally; one atom does not attract the shared electrons more strongly than the other atom (Figures 2.5a –.d). Principles of Human Anatomy and Physiology, 11e

26. Covalent Bonds • Atoms share electrons to form covalent bonds • Electrons spend most of the time between the 2 atomic nuclei • single bond = share 1 pair • double bone = share 2 pair • triple bond = share 3 pair • Polar covalent bonds share electrons unequally between the atoms involved Principles of Human Anatomy and Physiology, 11e

27. Polar Covalent Bonds • Unequal sharing of electrons between atoms. (Figure 2.6). • In a water molecule, oxygen attracts the hydrogen electrons more strongly • Oxygen has greater electronegativity as indicated by the negative Greek delta sign. Principles of Human Anatomy and Physiology, 11e

28. Hydrogen Bonds • Approximately 5% as strong as covalent bonds • Useful in establishing links between molecules or between distant parts of a very large molecule • Large 3-D molecules areoften held together by a large number of hydrogen bonds. Principles of Human Anatomy and Physiology, 11e

29. Hydrogen Bonds Hydrogen bonds are weak intermolecular bonds; they serve as links between molecules (usually). • help determine three-dimensional shape (Figure 2.7) • give water considerable cohesion which creates a very high surface tension Principles of Human Anatomy and Physiology, 11e

30. Chemical Reactions • New bonds form and/or old bonds are broken. • Metabolism is “the sum of all the chemical reactions in the body.” • Law of conservation of mass • The total mass of reactants equals the total mass of the products. (Count the number of atoms of each element below.) Principles of Human Anatomy and Physiology, 11e

31. CHEMICAL REACTIONS • A chemical reaction occurs when new bonds are formed or old bonds break between atoms (Figure 2.8). • The starting substances of a chemical reaction are known as reactants. • The ending substances of a chemical reaction are the products. • Remember: In a chemical reaction, the total mass of the reactants equals the total mass of the products (law of conservation of mass). • Metabolism refers to all the chemical reactions occurring in an organism and involves links between chemical reactions in different parts of the body, or even different parts of a cell. Principles of Human Anatomy and Physiology, 11e

32. Forms of Energy and Chemical Reactions • Energy is the capacity to do work. • Kinetic energy is the energy associated with matter in motion. • Temperature is an indirect measure of molecular motion. • Potential energy is energy stored by matter due to its position. • Chemical energy is a form of potential energy stored in the bonds of compounds or molecules. • The total amount of energy present at the beginning and end of a chemical reaction is the same; energy can neither be created nor destroyed although it may be converted from one form to another (law of conservation of energy). Principles of Human Anatomy and Physiology, 11e

33. Energy and Chemical Reactions Example: Chemical reactions involve energy changes. • forms of energy • eg., bonds within sugar molecules • potential energy = stored energy • eg., molecular vibration measured as temperature • kinetic energy = energy of motion • If the chemical bonds within sugar are broken, energy of sugar can be used to heat the body or create movement. Principles of Human Anatomy and Physiology, 11e

34. Energy Transfer in Chemical Reactions • An exergonic reaction is one in which the bond being broken has more energy than the one formed so that extra energy is released, usually as heat (occurs during catabolism of food molecules). • An endergonic reaction is just the opposite and thus requires that energy be added, usually from a molecule called ATP, to form a bond, as in bonding amino acid molecules together to form proteins. Principles of Human Anatomy and Physiology, 11e

35. Energy Transfer in Chemical Reactions • Reactions in living systems usually involve both kinds of reactions occurring together. • exergonic reactions release energy • endergonic reactions absorb energy • You will learn of many examples in human metabolism that involve coupled exergonic and endergonic reactions; the energy released from one reaction will drive the other. • Glucose breakdown releases energy, which is used to build ATP molecules (that store the energy for later use in other reactions.) Principles of Human Anatomy and Physiology, 11e

36. Activation Energy • Atoms, ions & moleculesare continuously moving& colliding. • Activation energy is thecollision energy needed to break bonds & begin areaction. • Increases in concentration & temperature, increase the probability of collision • more particles are in a given space when the concentration is higher • particles move more rapidly when temperature is raised Principles of Human Anatomy and Physiology, 11e

37. Activation Energy • Example: Firewood does not spontaneously combust. Why? Give an example of an oxidation reaction that has a relatively low activation energy. Principles of Human Anatomy and Physiology, 11e

38. Factors that influence the chance that a collision will occur and cause a chemical reaction include: • Concentration • Temperature • Catalysts are chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur (Figure 2.10). • A catalyst does not alter the difference in potential energy between the reactants and products. It only lowers the amount of energy needed to get the reaction started. • A catalyst helps to properly orient the colliding particles of matter so that a reaction can occur at a lower collision speed. • The catalyst itself is unchanged at the end of the reaction; it is often re-used many times. Principles of Human Anatomy and Physiology, 11e

39. Effectiveness of Catalysts • Catalysts speed up chemical reactions by lowering the activation energy. Principles of Human Anatomy and Physiology, 11e

40. Catalysts or Enzymes Example: • Normal body temperatures and concentrations are low enough that many chemical reactions are effectively blocked by the activation energy barrier. • Lactose typically reacts very slowly with water to break down into two simple sugars called glucose and galactose. • Lactase, an enzyme (catalyst) orients the colliding particles (lactose and water) properly so that they touch at the spots that make the reaction happen. • Thousands of lactose/water reactions may be catalyzed by one lactase enzyme. • Without lactase, the lactose will remain undigested in the intestines and often causes diarrhea and cramping. Principles of Human Anatomy and Physiology, 11e

41. Types of Chemical Reactions • Synthesis reactions occur when two or more atoms, ions, or molecules combine to form new and larger molecules. These are anabolic reactions, meaning that bonds are formed. (Figure 2.8) • In a decomposition reaction, a molecule is broken down into smaller parts. These are catabolic reactions, meaning that chemical bonds are broken in the process. • Exchange reactions involve the replacement of one atom or atoms by another atom or atoms. • In reversible reactions, end products can revert to the original combining molecules. Principles of Human Anatomy and Physiology, 11e

42. Synthesis Reactions--Anabolism • Two or more atoms, ions or molecules combine to form new & larger molecules • All the synthesis reactions in the body together are called anabolism • Usually are endergonic because they absorb more energy than they release • Example • combining amino acids to form a protein molecule Principles of Human Anatomy and Physiology, 11e

43. Decomposition Reactions--Catabolism • Large molecules are split into smaller atoms, ions or molecules • All decomposition reactions occurring together in the body are known as catabolism • Usually are exergonic since they release more energy than they absorb Principles of Human Anatomy and Physiology, 11e

44. Exchange Reactions • Substances exchange atoms • consist of both synthesis and decomposition reactions • Example • HCl + NaHCO3 gives rise to H2CO3 + NaCl • ions have been exchanged between substances Principles of Human Anatomy and Physiology, 11e

45. Reversible Reactions • Chemical reactions can be reversible. • Reactants can become products or products can revert to the original reactants • Indicated by the 2 arrows pointing in opposite directions between the reactants and the products AB A + B Principles of Human Anatomy and Physiology, 11e

46. Oxidation-Reduction Reactions • Oxidation is the loss of electrons from a molecule (decreases its potential energy) • acceptor of the electron is often oxygen • commonly oxidation reactions involve removing a hydrogen ion (H+) and a hydride ion (H-) from a molecule • equivalent to removing 2 hydrogen atoms = 2H • Reduction is the gain of electrons by a molecule • increases its potential energy • In the body, oxidation-reduction reactions are coupled & occur simultaneously Principles of Human Anatomy and Physiology, 11e

47. INORGANIC COMPOUNDS AND SOLUTIONS • Inorganic compounds usually lack carbon and are simple molecules; whereas organic compounds always contain carbon and hydrogen, usually contain oxygen, and always have covalent bonds. Principles of Human Anatomy and Physiology, 11e

48. Water • Water is the most important and abundant inorganic compound in all living systems. • An important property of water is its polarity, the uneven sharing of valence electrons that confers a partial negative charge near the one oxygen atom and two partial positive charges near the two hydrogen atoms in the water molecule (Figure 2.6). • Water enables reactants to collide to form products Principles of Human Anatomy and Physiology, 11e

49. Water in Chemical Reactions • Water is the ideal medium for most chemical reactions in the body and participates as a reactant or product in certain reactions. • Hydrolysis breaks large molecules down into simpler ones by adding a molecule of water. • Dehydration synthesis occurs when two simple molecules join together, eliminating a molecule of water in the process. Principles of Human Anatomy and Physiology, 11e

50. Water as a solvent • In a solution the solvent dissolves the solute. • Substances which contain polar covalent bonds and dissolve in water are hydrophilic, while substances which contain non polar covalent bonds are hydrophobic. • The polarity of water and its bent shape allow it to interact with several neighboring ions or molecules. (Figure 2.11) • Water’s role as a solvent makes it essential for health and survival. Principles of Human Anatomy and Physiology, 11e