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Biological Science Seventh Edition Chapter 2 Water and Carbon: The Chemical Basis of Life Copyright © 2020, 2017, 2014 Pearson...

Biological Science Seventh Edition Chapter 2 Water and Carbon: The Chemical Basis of Life Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Chapter 2 Opening Roadmap Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved © 2017 Pearson Education, Inc. 2.1 Atoms, Ions, and Molecules: The Building Blocks of Chemical Evolution – Atoms are made up of protons, neutrons and electrons. – Nucleus made up of protons and neutrons: ▪ Protons—positive charge (+1) ▪ Neutrons—neutral charge – Electrons are in orbitals outside the nucleus ▪ Negative charge (-1) – Atom with equal number of protons and electrons are electrically neutral Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Basic Atomic Structure (2 of 8) Elements: – Consist entirely of a single type of atom Atomic number: – Characteristic number of protons in nucleus of any atom – Written as subscript left of its symbol Mass number: – Sum of protons and neutrons in atom Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Basic Atomic Structure (3 of 8) Dalton (Da): – Each proton and each neutron has a mass of one dalton (Da) Mass of electron so small that it can be ignored Therefore, mass of atom is equal to its mass number Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Basic Atomic Structure (4 of 8) Number of protons in element does not vary: – Neutrons in element may vary – Forms element with different numbers of neutrons (isotope): ▪ Isotopes of element have different masses Example: All carbon atoms have 6 protons: – Carbon-12 has 6 neutrons; atomic mass 12 Da – Carbon-13 has 7 neutrons; atomic mass 13 Da – Carbon 14 has 8 neutrons; atomic mass 14 Da Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.3 The Atomic Structure of the First 18 Elements C, H, N, O, P and S make up over 99% of the atoms in the body Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Basic Atomic Structure Outermost shells of elements: – Atom’s valence shell is outermost shell – Electrons in this shell called valence electrons – Number of unpaired valence electrons is called the valence of an atom Different atoms have different numbers of unpaired electrons Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved How Does Covalent Bonding Hold Molecules Together? Atoms become more stable by making covalent bonds Example: Hydrogen does not have full valence shell: ▪ Two hydrogen atoms share electrons ▪ Outer shell of both atoms is filled—more stable Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Nonpolar and Polar Covalent Bonds Compounds: – Electrons in covalent bond not always shared equally – Compounds are molecules in which atoms of different elements are bonded together – Pull shared electrons toward their nuclei with varying strengths (electronegativity) Electronegativity: – Strength with which atoms pull electrons toward themselves – For the biologically abundant elements, O > N > S,C,H,P Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.5 Electron Sharing and Bond Polarity Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Ionic Bonding, Ions, and the Electron- Sharing Continuum (1 of 2) Unlike in a covalent bond, electron is not shared; it is completely transferred from one atom to another: – Transfer gives each atom a full valence shell Ions—atom or molecule that carries charge: – Cation—Atom loses electron and becomes positively charged – Anion—Atom gains an electron and becomes negatively charged Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.6 Ion Formation and Ionic Bonding Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.7 The Electron-Sharing Continuum Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved We will discuss later in the mitochondrion unit: the potential energy stored in nonpolar covalent bonds is higher than that stored in polar covalent bonds. Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved 2.2 Properties of Water and the Early Oceans Life is based on water: – 75% of cell is water Water is small and forms extensive hydrogen bonds with itself and with polar groups on nearby molecules. This leads to several properties which make it especially important in life’s chemistry. 1. Excellent solvent 2. Cohesive and adhesive properties 3. Solid (ice) is less dense than liquid 4. High thermal capacity (specific heat and heat of vaporization) Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.11 Water Is Polar and Participates in Hydrogen Bonds Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved 1. Water Is an Efficient Solvent Hydrogen bonds can also form between water molecules and polar solutes Hydrophilic (“water-loving”) molecules: ▪ Ions and polar molecules stay in solution due to their interactions with water’s partial charges Hydrogen bonding makes it possible for almost any charged or polar molecule to dissolve in water Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.12b Polar Molecules and Ionic Compounds Dissolve Readily in Water Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Water Is an Efficient Solvent (3 of 3) Hydrophobic (“water-fearing”) molecules: – Uncharged and nonpolar compounds – Do not dissolve in water Hydrophobic molecules interact with each other through hydrophobic interaction (energy cost of breaking water’s hydrogen bonds) van der Waals interactions increase stability of clustered hydrophobic molecules Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Cohesion, Adhesion, and Surface Tension (1 of 3) Cohesion and adhesion: – Attraction between like molecules is called cohesion – Attraction between unlike molecules is called adhesion Water is cohesive: ▪ Stays together because of hydrogen bonds ▪ Adheres to surfaces with polar or charged components Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Water Is Denser as a Liquid than as a Solid Most substances shrink as they solidify Water expands as it freezes: – Denser as a liquid than a solid – Forms relatively open crystal structure – This is why ice floats! – Ice forms an insulating “blanket” on water surfaces – Figure 2.15 Hydrogen Bonding in Ice and Water Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.15 Hydrogen Bonding in Ice and Water Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Water Has a High Capacity for Absorbing Energy (1 of 2) Water has high capacity for absorbing energy: – Specific heat—amount of energy needed to raise temperature of 1 gram of substance by 1°C: ▪ Water has very high specific heat ▪ Many hydrogen bonds must be broken for water molecules to move faster Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Water Has a High Capacity for Absorbing Energy (2 of 2) Large amount of energy needed to break hydrogen bonds in liquid water Water’s heat of vaporization: – Energy required to change 1 gram of a substance from liquid to gas: ▪ Water has very high heat of vaporization ▪ Water has to absorb great deal of energy to evaporate ▪ Explains why sweating is an effective way to cool off Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved The Role of Water in Acid–Base Chemical Reactions (3 of 3) Acids—substances that give up protons during chemical reactions and raise hydronium ion concentration (H3O+): – Adding acid to solution increases proton concentration of solution Bases—substances that acquire protons during chemical reactions and lower (H3O+): ‒ Adding base to solution decreases proton concentration Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved The pH of a Solution Reveals Whether It Is Acidic or Basic (1 of 2) Concentration of protons in neutral water is very low (1 × 10-7M) pH (power of hydrogen): – Logarithmic notation used to express concentration of protons in solution – One unit of pH represents change in concertation of hydrogen ions equal to factor of 10 Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved The pH of a Solution Reveals Whether It Is Acidic or Basic (2 of 2) Acids have a pH of less than 7 Bases have a pH of greater than 7 Neutral indicates neither acidic or basic: – Solution inside living cells is about pH 7 Buffers minimize changes in pH: – Buffers help maintain homeostasis, relatively constant conditions, in organisms Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved 2.5 Life is Carbon Based Carbon: – Except for water, almost all molecules found in organisms have this atom – Forms four covalent bonds due to its four valence electrons Organic compounds—molecules that contain carbon bonded to other elements: – Limitless array of molecular shapes – With different combinations of single and double bonds Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 2.22 The Shapes of Carbon- Containing Molecules Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Functional Groups Define the Chemical Behavior of Organic Molecules Know these six functional functional groups found in organic compounds: – Amino groups attract proton and act as bases – Carboxyl groups drop proton and act as acids – Carbonyl groups have sites that link molecules into more-complex compounds – Hydroxyl groups are polar and hydrophilic – Phosphate groups have two negative charges – Sulfhydryl groups link together via disulfide bonds Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Table 2.3 Six Functional Groups Commonly Attached to Carbon Atoms Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved