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2-1 The Nature of Matter Atoms The study of chemistry begins with the basic unit of matter, the atom. Placed side by side, 100 million atoms would make a row only about 1 centimeter long. Atoms contain subatomic particles that are even smaller. The subatomic particles that make up atoms are a. protons b. neutrons c. electrons The subatomic particles in a helium atom. Elements and Isotopes A chemical element is a pure substance that consists entirely of one type of atom. – C stands for carbon. – Na stands for sodium. The number of protons in an atom of an element is the element's atomic number. Commonly found in living organisms: Isotopes Atoms of the same element that differ in the number of neutrons they contain are known as isotopes. Because they have the same number of electrons, all isotopes of an element have the same chemical properties. Radioactive Isotopes Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time Radioactive isotopes can be used: a. to determine the ages of rocks and fossils. b. to treat cancer. c. to kill bacteria that cause food to spoil. d. as labels or “tracers” to follow the movement of substances within an organism. Chemical Compounds A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. Chemical Formula Water H2O Table Salt NaCl Hydrochloric Acid HCl Glucose C6H12O6 Chemical Bonds The atoms in compounds are held together by chemical bonds. The electrons that are available to form bonds are called valence electrons. The main types of chemical bonds are: a. ionic bonds b. covalent bonds Ionic Bonds An ionic bond is formed when one or more electrons are transferred from one atom to another. These positively and negatively charged atoms are known as ions. Sodium atom (Na) Chlorine ion (Cl-) Sodium ion (Na+) Chlorine atom (Cl) Protons Electrons +11 - 11 10 Protons Electrons +17 18 - 17 Charge +10 Charge -10 Covalent Bonds Sometimes electrons are shared by atoms instead of being transferred. A covalent bond forms when electrons are shared between atoms. a. single covalent bond b. double bond c. triple bond The structure that results when atoms are joined together by covalent bonds is called a molecule. Van der Waals Forces When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby d molecules. d+ d- d+ Quiz 2-1 The particles that move around the nucleus of an atom are called a. neutrons. b. protons. c. electrons. d. isotopes. The atomic number of a carbon atom is 6. How many neutrons does the isotope carbon-14 have? a. 6 b. 8 c. 12 d. 14 Which of the following statements about the three isotopes of carbon is true? a. They are all radioactive. b. They have different numbers of electrons. c. They have the same chemical properties but differ in atomic mass. d. They have the same number of protons and neutrons. A chemical compound consists of a. Electrons mixed with neutrons. b. two or more elements combined in a definite proportion. c. two or more protons combined in any proportion. d. at least three elements combined by ionic or covalent bonds. Van der Waals forces are the result of a. unequal sharing of electrons. b. ionic bonds. c. the bonding of different isotopes. d. the chemical combination of sodium and chlorine. 2-2 Properties of Water A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. d+ d- Hydrogen Bonds Because of their partial positive and negative charges, polar molecules can attract each other. Cohesion is an attraction between molecules of the same substance. Because of hydrogen bonding, water is extremely cohesive. Adhesion is an attraction between molecules of different substances. Solutions and Suspensions A mixture is a material composed of two or more elements or compounds that are physically mixed but not chemically combined. Two types of mixtures can be made with water – solutions – suspensions Solutions All the components of a solution are evenly distributed throughout the solution. solute—the substance that is dissolved. solvent—the substance in which the solute dissolves. When a crystal of table salt is placed in warm water, sodium and chloride ions are attracted to the polar water molecules. Suspensions Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out easily. Acids, Bases, and pH A water molecule is neutral, but can react to form hydrogen and hydroxide ions. H2O H+ + OH- The pH scale Chemists devised a measurement system called the pH scale to indicate the concentration of H+ ions in solution. The pH scale ranges from 0 to 14. The pH Scale At a pH of 7, the concentration of H+ ions and OHions is equal. Acids An acid is any compound that forms H+ ions in solution. Bases A base is a compound that produces hydroxide ions (OH- ions) in solution. Buffers The pH of the fluids within most cells in the human body must generally be kept between 6.5 and 7.5. Controlling pH is important for maintaining homeostasis. Quiz 2-2 A molecule in which the charges are unevenly distributed is called a a. polar molecule. b. cohesive molecule. c. hydrogen molecule. d. covalent molecule. A dissolved substance is called a a. solvent. b. solution. c. solute. d. suspension. A compound that produces hydroxide ions in solution is called a(an) a. base. b. buffer. c. acid. d. salt. Hydrogen bonds between water molecules result from a. adhesion between water molecules. b. magnetic attractions between water molecules. c. uneven electron distribution in each water molecule. d. ionic bonds in the water molecule. On a pH scale, a value of 2 means that the solution has a. equal concentrations of H+ and OH- ions. b. the same concentration of H+ ions as pure water. c. higher concentration of H+ than in pure water. d. lower concentration of H+ than in pure water. The Chemistry of Carbon Organic chemistry is the study of all compounds that contain bonds between carbon atoms. Copyright Pearson Prentice Hall Macromolecules Macromolecules are formed by a process known as polymerization. Monomers Polymers Four groups of organic compounds found in living things are: a.carbohydrates b.lipids c.nucleic acids d.proteins Macromolecules! What is the function of carbohydrates? Source of Energy Structure Carbohydrates Carbohydrates are compounds made up of carbon, hydrogen, and oxygen atoms, usually in a ratio of 1 : 2 : 1. Different sizes of carbohydrates: •Monosaccharides • Glucose •Disaccharides • Sucrose •Polysaccharides • Starch Starches and sugars are examples of carbohydrates that are used by living things as a source of energy. Examples: Cellulose Starch Glycogen Starch Glucose Lipids Lipids are generally not soluble in water. The common categories of lipids are: fats oils waxes steroids Lipids can be used to store energy. Some lipids are important parts of biological membranes and waterproof coverings. Nucleic Acids Nucleic acids are polymers assembled from individual monomers known as nucleotides. Nucleotides consist of three parts: a.a 5-carbon sugar b.a phosphate group c.a nitrogenous base Nucleic acids store and transmit hereditary, or genetic, information. ribonucleic acid (RNA) deoxyribonucleic acid (DNA) Proteins Proteins are macromolecules that contain nitrogen, carbon, hydrogen, and oxygen. – polymers of molecules called amino acids. The portion of each amino acid that is different is a side chain called an R-group. The instructions for arranging amino acids into many different proteins are stored in DNA. Protein Molecule Amino Acids Some functions of proteins: –Control rate of reactions – Enzymes –Used to form bones and muscles –Transport substances into or out of cells –Help to fight disease - antibodies Quiz 2-3 Large carbohydrate molecules such as starch are known as a. lipids. b. monosaccharides. c. proteins. d. polysaccharides. Many lipids are formed from glycerol and a. fatty acids. b. monosaccharides. c. amino acids. d. nucleic acids. Proteins are among the most diverse macromolecules because a. they contain both amino groups and carboxyl groups. b. they can twist and fold into many different and complex structures. c. they contain nitrogen as well as carbon, hydrogen, and oxygen. d. their R groups can be either acidic or basic. Which of the following statements about cellulose is true? a. Animals make it and use it to store energy. b. Plants make it and use it to store energy. c. Animals make it and use it as part of the skeleton. d. Plants make it and use it to give structural support to cells. A major difference between polysaccharides and proteins is that a. plants make polysaccharides, while animals make proteins. b. proteins are made of monomers, while polysaccharides are not. c. polysaccharides are made of monosaccharides, while proteins are made of amino acids. d. proteins carry genetic information, while polysaccharides do not. Chemical Reactions A chemical reaction is a process that changes one set of chemicals into another set of chemicals. Copyright Pearson Prentice Hall The elements or compounds that enter into a chemical reaction are known as reactants. The elements or compounds produced by a chemical reaction are known as products. Energy Changes Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will not occur without a source of energy. When hydrogen gas reacts with oxygen to produce water vapor, it is an energyreleasing reaction in which energy is given off as heat. 2H2 + O2 2H2O How would you reverse this reaction? Activation Energy Chemists call the energy that is needed to get a reaction started the activation energy. Enzymes Some chemical reactions that make life possible are too slow or have activation energies that are too high. These chemical reactions are made possible by catalysts. Enzymes are Biological Catalysts. Enzymes speed up chemical reactions that take place in cells. The Enzyme-Substrate Complex Enzymes provide a site where reactants can be brought together to react, reducing the energy needed for reaction. The reactants of enzyme-catalyzed reactions are known as substrates. An Enzyme-Catalyzed Reaction Regulation of Enzyme Activity Enzymes can be affected by any variable that influences a chemical reaction. – pH values – Changes in temperature – Enzyme or substrate concentrations Quiz 2-4 The elements or compounds produced by a chemical reaction are known as a. reactants. b. enzymes. c. products. d. waste. Chemical reactions always involve a. changes in energy. b. enzymes. c. catalysts. d. changes in the atomic number of the reactants. The factor that prevents many energy-releasing reactions from occurring at relatively low temperatures is called a. catalytic energy. b. chemical bond energy. c. enzyme energy. d. activation energy. Which of the following statements is true? a. All proteins are enzymes. b. All catalysts are enzymes. c. All enzymes are catalysts. d. All catalysts are proteins. What happens to an enzyme after the reaction it catalyzes has taken place? a. The enzyme is destroyed, and the cell must make another. b. The enzyme holds on to the product until another enzyme removes it. c. The enzyme is unchanged and ready to accept substrate molecules. d. The enzyme changes shape so it can accept a different kind of substrate.