Transcript atom
THE PROCESS OF SCIENCE – What is science? – The word science is derived from a Latin verb meaning “to know.” Discovery Science • Science seeks natural causes for natural phenomena. – This limits the scope of science to the study of structures and processes that we can observe and measure. Hypothesis-Driven Science • As a formal process of inquiry, consists of a series of steps. – The key element of the scientific method is hypothesis-driven science. Hypothesis-Driven Science – As a formal process of inquiry, the scientific method consists of a series of steps. • The key element of the scientific method is hypothesis-driven science. Revise and repeat Observation Question Hypothesis Prediction Experiment Hypothesis-Driven Science Observation: My flashlight doesn’t work. Question: What’s wrong with my flashlight? Hypothesis: The flashlight’s batteries are dead. Prediction: If I replace the batteries, the flashlight will work. Experiment: I replace the batteries with new ones. Experiment supports hypothesis; make additional predictions and test them. Theories in Science – What is a scientific theory, and how is it different from a hypothesis? • A theory is much broader in scope than a hypothesis. • Theories only become widely accepted in science if they are supported by an accumulation of extensive and varied evidence. Chemistry of Life – Matter is anything that occupies space and has mass. – Matter is found on the Earth in three physical states: • Solid • Liquid • Gas Atoms – Each element consists of one kind of atom. • An atom is the smallest unit of matter that still retains the properties of an element. 2 Protons 2 Neutrons 2 Electrons Nucleus Nucleus Cloud of negative charge 2 electrons Chemistry of Life – Matter is composed of chemical elements. • Elements are substances that cannot be broken down into other substances. Change the number of PROTONS in the nucleus and you change the ELEMENT Chemistry of Life – Elements differ in the number of subatomic particles in their atoms. • The number of protons, the atomic number, determines which element it is. • An atom’s mass number is the sum of the number of protons and neutrons. • Mass is a measure of the amount of matter in an object. Periodic Table of the Elements Legend Solid Liquid Gas Synthetic Alkali metals Alkali earth metals Transition metals Rare earth metals Other metals Noble gases Halogens Other nonmetals Atomic number = number of protons within the nucleus Chemistry of Life – Twenty-five elements are essential to life. – Four elements make up about 96% of the weight of Carbon C: 18.5% the human body: • Oxygen Calcium Ca: 1.5% Phosphorus P: 1.0% Oxygen O: • Carbon 65.0% Potassium K: 0.4% Sulfur S: 0.3% • Hydrogen Sodium Na: 0.2% Chlorine Cl: 0.2% • Nitrogen Magnesium Mg: 0.1% Hydrogen H: 9.5% Nitrogen N: 3.3% Trace elements: less than 0.01% Boron B Chromium Cr Cobalt Co Copper Cu Fluorine F Iodine I Iron Fe Manganese Mn Molybdenum Mo Selenium Se Silicon Si Tin Sn Vanadium V Zinc Zn Chemical Properties of Atoms – Electrons determine how an atom behaves when it encounters other atoms. First electron shell can hold 2 electrons Electron Outer electron shell can hold 8 electrons Hydrogen H Carbon C Atomic number = 1 Atomic number = 6 © 2010 Pearson Education, Inc. Nitrogen N Atomic number = 7 Oxygen O Atomic number = 8 Covalent Bonds – A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. – Atoms held together by covalent bonds form a molecule. Name Electron configuration molecular formula Hydrogen gas H2 Structural formula Space-filling model Single bond a pair of shared electrons Oxygen gas O2 Double bond two pairs of shared electrons Methane CH4 Ball-and-stick model Ionic Bonds – When an atom loses or gains electrons, it becomes electrically charged. • Charged atoms are called ions. • Ionic bonds are formed between oppositely charged ions. Outer shell has 1 electron The outer electron is stripped from sodium and completes the chlorine atom’s outer shell Complete outer shells Outer shell has 7 electrons Na Sodium atom Cl Chlorine atom Na Sodium ion Cl Chlorine ion Sodium chloride (NaCl) The attraction between the ions—an ionic bond—holds them together Hydrogen Bonds – Water is a compound in which the electrons in its covalent bonds are shared unequally. • This causes water to be a polar molecule, one with opposite charges on opposite ends. slightly slightly H H O slightly – Hydrogen bonding • Weak bonds formed between hydrogen and another atom – Surface tension of water • Important as intramolecular bonds, giving shape to proteins and other biomolecules WATER AND LIFE – Life on Earth began in water and evolved there for 3 billion years. • Modern life remains tied to water. • Your cells are composed of 70%–95% water. Properties of Water • Numerous properties due to the hydrogen bonding Properties of Water – Water molecules stick together as a result of hydrogen bonding. Evaporation from the leaves • This is called cohesion. Microscopic tubes SEM Cohesion due to hydrogen bonds between water molecules Properties of Water – Heat and temperature are related, but different. • Heat is the amount of energy associated with the movement of the atoms and molecules in a body of matter. • Temperature measures the intensity of heat. – Water can absorb and store large amounts of heat while only changing a few degrees in temperature. – Water can moderate temperatures. Properties of Water – Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid. • Hydrogen bonds give water an unusually high surface tension. Water is the solvent of life *solution *solvent *solute *aqueous solution Acids, Bases and pH Oven cleaner Increasingly basic lower H concentration Basic solution 14 Neutral solution Acidic solution Increasingly acidic greater H concentration Neutral [H+] [OH–] 13 Household 12 bleach Household ammonia 11 Milk of magnesia 10 9 Seawater 8 Human blood 7 Pure water 6 Urine 5 4 Tomato juice 3 Grapefruit juice, soft drink 2 Lemon juice, gastric juice 1 0 pH scale Carbon and Organic Chemistry – Carbon is a versatile atom. – Carbon forms large, complex, and diverse molecules necessary for life’s functions. – Organic compounds are carbon-based molecules. Structural formula Ball-and-stick model Space-filling model Carbon and Organic Chemistry • Variations in Carbon skeletons Carbon skeletons vary in length Carbon skeletons may be unbranched or branched Carbon skeletons may have double bonds, which can vary in location Carbon skeletons may be arranged in rings Hydrocarbons – Larger hydrocarbons form fuels for engines. – Hydrocarbons of fat molecules fuel our bodies. Carbon and Organic Chemistry • The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton – These atoms are called functional groups – Some common functional groups include: Hydroxyl group Carbonyl group Amino group Carboxyl group Found in alcohols and sugars Found in sugars Found in amino acids and urea in urine (from protein breakdown) Found in amino acids, fatty acids, and some vitamins Macromolecules – On a molecular scale, many of life’s molecules are gigantic, earning the name macromolecules. – Three categories of macromolecules are • Carbohydrates • Proteins • Nucleic acids Macromolecules *most macromolecules are polymers polymer monomer The making and breaking of polymers: Dehydration reaction: Hydrolysis: Carbohydrates • Carbohydrates include – Small sugar molecules in soft drinks • Monosaccharides & Disaccharides – Long starch molecules in pasta and potatoes • Polysaccharides Monosaccharides • Monosaccharides are simple sugars – Glucose, found in sports drinks – Fructose, found in fruit • Honey contains both glucose and fructose Glucose Fructose Isomers Monosaccharides • In aqueous solutions, monosaccharides form rings (b) Abbreviated ring structure (a) Linear and ring structures Disaccharides • A disaccharide is a double sugar • Disaccharides are joined by the process of dehydration synthesis Glucose Glucose Maltose Disaccharides • The most common disaccharide is sucrose, common table sugar – It consists of a glucose linked to a fructose – Sucrose is extracted from sugar cane and the roots of sugar beets Polysaccharides – They are long chains of sugar units – They are polymers of monosaccharides Glucose monomer Starch granules in potato tuber cells (a) Starch Glycogen Granules In muscle tissue (b) Glycogen Cellulose fibril in a plant cell wall Cellulose molecules (c) Cellulose Polysaccharides • Most animals cannot derive nutrition from fiber – How do grazing animals survive on a diet of cellulose? Proteins • Proteins perform most of the tasks the body needs to function – They are the most elaborate of life’s molecules MAJOR TYPES OF PROTEINS Structural Proteins Storage Proteins Contractile Proteins Transport Proteins Enzymes The Monomers: Amino Acids • All proteins are constructed from a common set of 20 kinds of amino acids Amino Carboxyl group group Side group Proteins as Polymers • Cells link amino acids together by dehydration synthesis – The resulting bond between them is called a peptide bond Carboxyl group Amino group Side group Side group Amino acid Amino acid Dehydration synthesis Side group Side group Peptide bond Protein Structure – The arrangement of amino acids makes each protein different • Primary structure – The specific sequence of amino acids in a protein 5 1 15 10 30 35 20 25 45 40 50 55 65 60 70 85 80 75 95 90 100 110 105 115 120 125 129 Amino acid Protein Structure • A slight change in the primary structure of a protein affects its ability to function – The substitution of one amino acid for another in hemoglobin causes sickle-cell disease 1 2 (b) Sickled red blood cell 6 7. . . 146 4 5 Normal hemoglobin (a) Normal red blood cell 1 3 2 3 6 7. . . 146 4 5 Sickle-cell hemoglobin Protein Structure • Proteins have four levels of structure Hydrogen bond Pleated sheet Polypeptide (single subunit) Amino acid (a) Primary structure Complete protein, with four polypeptide subunits Hydrogen bond Alpha helix (b) Secondary structure (c) Tertiary structure (d) Quaternary structure