Chapter 2

1. Chapter 2 The Chemical Basis of Life

2. Basic Chemistry • Matter, Mass, and Weight • Matter: Anything that occupies space and has mass • Mass: The amount of matter in an object • Weight: The gravitational force acting on an object of a given mass • Elements and Atoms • Elements: The simplest type of matter with unique chemical properties • 112 known elements (92 naturally occurring) • Atoms: Smallest particle of an element that has chemical characteristics of that element

3. Atoms: composed of subatomic particles Neutrons: no electrical charge Protons: positive charge Electrons: negative charge Nucleus Formed by protons and neutrons Most of volume of atom occupied by electrons Relative size: gumball vs. stadium. Atomic Structure

4. Atomic Structure • Atomic Symbol • Atomic Number: Equal to the number of protons in an atom. • Mass Number: Number of protons and neutrons in an atom.

5. Atomic number • Equal to the number of protons in each atom • Mass number • Equal to the number of protons and neutrons in each atom • Electrons determine the chemical properties of the atom. • Electron shells - Electrons encircle the nucleus in electron shells or energy levels. • Orbital - an electron can occupy any position in a certain volume of space called an orbital • The innermost shell can hold up to two electrons. • The outermost shell, holding the valence electrons, can have eight electrons.

6. Atomic Configuration • Electrons with least amount of potential energy are located in K shell closest to nucleus; electrons having more potential energy are located in shells farther from the nucleus. • Inner shell contains up to two electrons; additional shells contain eight electrons. • Periodic table is arranged according to number of electrons in outer shell. • Electron arrangement is determined by total number of electrons and electron shell they occupy. (Bohr Model)

8. Atomic Structure of Isotopes • Isotopes have the same atomic number but a different mass. • same number of protons but differ in the number of neutrons • e.g., a carbon atoms has six protons but may have more or less than usual six neutrons.

9. Isotopes • Two or more forms of the same element that have the same number of protons and electrons but have a different number of neutrons.

10. Atomic Mass • Individual atoms have very little mass. • Hydrogen = 1.67 X 10 -24g. • Unified atomic mass units (u) or Dalton (D) • Proton or neutron has an atomic mass of 1 . • Atomic Mass = the average mass of its naturally occurring isotopes taking into account the relative abundance of each isotope. • Carbon has the isotopes 12C, 13C and 14C. • The atomic mass of Carbon is 12.01 D

11. Electrons and Chemical Bonding • The chemical behavior of an atom is determined largely by its outermost electrons (valence electrons). • Chemical bonding occurs when the outermost electrons are transferred or shared between atoms. • Chemical bonding can be grouped into categories: Ionic, covalent, metallic and hydrogen bonds

12. Ionic Bonding • Ions are charged particles. • cations -Positively charged ions ( have lost an electron) • anions - Negatively charged ions (have gained an electron) • Oppositely charged molecules are attracted to each other and tend to remain close to each other. • Ionic bonding occurs when one or more valence electrons from one atom are completely transferred to a second atom. • Common ions found in the body include: • Ca++, Na+, K+, H+, OH-, Cl- • Ionic compounds readily form crystals. • Ionic bonds tend to dissociate in water.

16. Covalent Bonding • Covalent bonding: atoms share one or more pairs of valence electrons to form stable valence shells. • Single covalent bond: One electron pair is shared between two atoms. • Double covalent bond: Two atoms share 4 electrons • Polar and non polar covalent bonds • Nonpolar covalent bond: Electrons are shared equally • Polar covalent bonds: Electrons are not shared equally

22. Intermolecular Forces • Result from weak electrostatic attractions between oppositely charged parts or molecules, or between ions and molecules • Weaker than forces producing chemical bonding

23. Hydrogen Bonding • Hydrogen bond: Weak attractive force between slightly positive hydrogen atom of one molecule and slightly negative atom in another molecule • Many hydrogen bonds taken together are relatively strong. • Hydrogen bonds between complex molecules of cells help maintain structure and function.

25. Intermolecular Forces • Solubility: Ability of one substance to dissolve in another • Example: Sugar dissolves in water • Dissociation or Separation • Ionic compounds • Cations are attracted to negative end and anions attracted to positive end of water molecules

26. Intermolecular Forces • Electrolytes: Cations (+) and anions (-) that dissociate in water • Capacity to conduct an electric current • Currents can be detected by electrodes • Nonelectrolytes: Molecules that do not dissociate form solutions that do not conduct electricity

27. Chemical Reactions • Chemical Reactions: Atoms, ions, molecules or compounds interact to form or break chemical bonds • Metabolism: All anabolic and catabolic reactions in the body • Catabolism: Decomposition reactions • Hydrolysis: Reactions that use water • Anabolism: Growth, maintenance, and repair of the body in synthesis reactions • Produce molecules characteristic of life: ATP, proteins, carbohydrates, lipids, and nucleic acids

28. Synthesis and Decomposition Reactions • Synthesis Reactions • Two or more reactants chemically combine to form a larger product • Anabolism: All body’s synthesis reactions • Decomposition Reactions • Reverse of synthesis reactions • Catabolism: Reactions of decomposition in body

30. Oxidation-Reduction Reactions • Oxidation • Loss of an electron by an atom • Reduction • Gain of an electron by an atom • Oxidation-Reduction Reactions • The complete or partial loss of an electron by one atom is accompanied by the gain of that electron by another atom

31. Rate of Chemical Reactions • Reactant type - differ in their ability to undergo chemical reactions. • Concentration - greater concentrations of reactants generally cause reactions to proceed faster. • Temperature - reaction speed increases with higher temps. • Catalysts - substance that increases the rate at which a chemical reaction proceeds. • Enzymes - are protein molecules that act as catalysts in the body.

32. Energy • Energy: The capacity to do work • Potential Energy: Stored energy • Kinetic Energy: Does work and moves matter • Mechanical Energy: Energy resulting from the position or movement of objects • Chemical Energy: Form of potential energy in the chemical bonds of a substance • Heat Energy: Energy that flows between objects of different temperatures

33. Energy and Chemical Reactions

34. Speed of Chemical Reactions • Activation Energy: Minimum energy reactants must have to start a chemical reaction • Catalysts: Substances that increase the rate of chemical reactions without being permanently changed or depleted • Enzymes: Increase the rate of chemical reactions by lowering the activation energy necessary for reaction to begin

35. Activation Energy and Enzymes

36. Properties of Water- functions in living organisms • Stabilizing body temperature • Water has a high specific heat and tends to resist large temperature fluctuations. • Evaporation (540 calories / gram of water). • Protection • Lubricant and Cushion • Chemical reactions • Water is an excellent solvent.

38. Mixing medium • solutions: any liquid that contains dissolved substances • suspensions: a liquid that contains non-dissolved materials that settle out of of the liquid unless it is continually shaken. • colloid: a liquid that contains non-dissolved materials that do not settle out of liquid. (Water and proteins inside the cell).

42. Solution Concentrations • Solutions = solvent (the liquid portion) + solutes (substances dissolved in the solvent). • Concentration - expressed in a number of different ways: • percent solution (10% solution = 10 g solute / 100 ml of solvent) • Osmolarity (1 osmole = 1 mole (Avegadro’s # of particles) in 1 kilogram of water). • Osmolarity is a reflection of the number of particles in a solution and not the type of particle in a solution. • The osmolarity of body fluids = 300 mOsm • important because it influences the movement of water in and out of cells. • Note: difference between molality and osmolality is that osmolality takes into acount the number of particles a molecule breaks into when it goes into solution.

43. Acids and Bases When water ionizes or dissociates, it releases a small (107 moles/liter) but equal number of H+ and OH ions; Thus its ph is neutral. Acid: a proton donor. Base: a proton acceptor. • Take up hydrogen ions or release hyroxide ions. • Stong vs Weak acids. -The more freely the acid or base dissociates the stronger it is. • Strong acid : HCl ºH+ Cl- dissociates almost completely • Weak Acid : Acetic acid CH3COOH º CH3COO- + H + • Some dissociates and some does not.

44. pH Scale • The pH scale indicates acidity and basicity (alkilinity) of a solution. • Measure of free hydrogen ions as a negative logarithm of the H+ concentration (-log [H+]). • logarithmic scale - a change of pH by one unit represents a 10 fold change in the concentration of H+.

45. pH Scale continued • pH values range from 0 (100 moles/liter; most acidic) to 14 (1014 moles/liter; most basic). • One mole of water has 107 moles/liter of hydrogen ions; therefore, has neutral pH of 7. • Acid has a pH less than 7 • Base has a pH greater than 7. • Normal Range in body = 7.35 - 7.45 • Acidosis - Nervous system depression, disorientation and coma. • Alkalosis - N. S. overexcited, convulsion - possibly fatal.

48. Buffers • Buffers keep pH steady and within normal limits in living organisms. • Buffers stabilize pH of a solution by taking up excess hydrogen or hydroxide ions. • Carbonic acid helps keep blood pH within normal limits: • H2CO3 H+ + HCO3-. • The chemical nature of many molecules changes as the pH of a solution in which they are dissolved changes. • Most enzymes work within a narrow pH range. • Survival of an organism depends on its ability to maintain it pH level within a narrow range.