Chapter 2: The Chemical Basis of Life PDF

9/19/2023 Because learning changes everything. ® Chapter 2 The Chemical Basis of Life Essentials of Biology SEVENTH EDITION Sylvia S. Mader Michael...

9/19/2023 Because learning changes everything. ® Chapter 2 The Chemical Basis of Life Essentials of Biology SEVENTH EDITION Sylvia S. Mader Michael Windelspecht © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 2.1 Atoms and Atomic Bonds Matter: Refers to anything that takes up space and has mass Can exist as a solid, liquid, or gas, or plasma Composed of elements Element—substance that cannot be broken down into another substance by ordinary chemical means Only 92 naturally occurring elements Four elements make up about 96% of the body weight of most living organisms—carbon, hydrogen, oxygen, and nitrogen What are some other elements? © McGraw Hill LLC 2 1  9/19/2023 Where Do Elements Come from? Normal chemical reactions do not produce elements. The majority of heavier elements such as iron are produced when a star explodes, producing a supernova. Supernovas scatter heavier elements into space, which then become parts of planets. We came from the primordial goo, from Earth. Therefore, we are made of stars. The iron in blood was formed from the explosion of stars. “After all, what nobler thought can one cherish than that the universe lives within us all?” Neil deGrasse Tyson © McGraw Hill LLC 3 Figure 2.1 Elements in Living Organisms including zinc and chromium Access the text alternative for slide images. © McGraw Hill LLC (photo): PNC/Getty Images 4 2  9/19/2023 Atomic Structure 1 Atomic theory states that elements consist of atoms. Atom: a tiny particle that cannot be subdivided into smaller substances without losing its properties Properties of atoms (subatomic particles): Protons (p+): positively charged, found in the nucleus Neutrons (n0): no charge, also found in the nucleus Electrons (e-): negatively charged, found outside of nucleus moving in orbitals What are orbitals? © McGraw Hill LLC 5 Models of Atomic Structure © McGraw Hill LLC 3  9/19/2023 Figure 2.2 Two Models of Helium (He) Access the text alternative for slide images. © McGraw Hill LLC 7 Atomic Structure 2 Atomic symbol—name of the atom or element H for hydrogen or Na for sodium Mass number is equal to sum of protons and neutrons— electrons have about zero mass. © McGraw Hill LLC 8 4  9/19/2023 Atomic Number All atoms of an element have this same number of protons. Also gives number of electrons if an atom is electrically neutral Note: The How many protons does Nitrogen have? Atomic Number Phosphorus? tells you the number of How many neutrons does protons in an Oxygen have? atom. How many electrons does Calcium have? © McGraw Hill LLC 9 Periodic Table Elements’ chemical and physical characteristics recur in a predictable manner. Atoms are arranged in periods (rows) and groups (columns). © McGraw Hill LLC 10 5  9/19/2023 Access the text alternative for slide images. © McGraw Hill LLC 11 Isotopes 1 Isotopes: Atoms of the same element that differ in the number of neutrons. Isotopes have the same number of protons but a different number of neutrons (different mass numbers). Unstable and may decay, emitting radiation. Radioactive isotope behavior is essentially the same as a stable isotope of same element. Can be used as tracer—PET scan What is an example of an Can cause damage to cells, leading to cancer isotope? Can be used to sterilize medical equipment © McGraw Hill LLC 12 6  9/19/2023 Isotopes 2 Carbon isotopes come in three forms. By far the most common isotope of carbon is carbon-12 (12C), which contains six neutrons in addition to its six protons. The next heaviest carbon isotope, carbon-13 (13C), has seven neutrons. Both 12C and 13C are called stable isotopes since they do not decay into other forms or elements over time. The rare carbon-14 (14C) isotope contains eight neutrons in its nucleus. Unlike 12C and 13C, this isotope is unstable, or radioactive. Over time, a 14C atom will decay into a stable product. Carbon-14 dating: a scientific method that can accurately determine the age of organic materials as old as approximately 60,000 years. Living organisms—like trees, plants, people, and animals—absorb carbon-14 into their tissue. When they die, the carbon-14 starts to change into other atoms over time. Scientists can estimate how long the organism has been dead by counting the remaining carbon-14 atoms. © McGraw Hill LLC 13 Arrangement of Electrons in an Atom 1 Electrons are constantly moving. Useful to construct models of atoms with energy levels or electron shells Each shell contains a certain number of electrons. Orbitals: Pathways in which electrons rotate around the nucleus Represent volumes of space in which an electron is likely to be found © McGraw Hill LLC 14 7  9/19/2023 Arrangement of Electrons in an Atom 2 For atoms up through number 20 Two electrons fill first shell, Eight electrons fill each additional shell Octet rule for valence shell Valence shell—outermost shell Valence: The number of electrons in the outermost shell of an element Determines the degree of reactivity and the type of bonds an element can make If an atom has more than two shells, the outer shell is most stable with eight electrons Atoms can give up, accept, or share electrons to have eight. Chemical properties of atoms are largely determined by the arrangement of their electrons. © McGraw Hill LLC 15 Bonds and Molecules Molecule: A chemical substance that results from the combination of two or more atoms O2, N2 Compound: A molecule composed of two or more different elements H2O, C6H12O6, NaCl, CO2, MgCl2 © McGraw Hill LLC 16 8  9/19/2023 Types of Chemical Bonds Chemical bonds: Result when two or more atoms share, donate (lose), or accept (gain) electrons Types of chemical bonds: Ionic—attraction (lose/gain) between opposite charges Covalent—sharing electrons to complete outer shell Hydrogen—attraction between two atoms that already participate in other chemical bonds. One of the atoms is hydrogen, while the other may be any electronegative atom, such as oxygen, chlorine, or fluorine. © McGraw Hill LLC 17 Three Types of Bonding © McGraw Hill LLC 9  9/19/2023 Types of Chemical Bonds: Ionic 1 Ionic bonding: Forms when two atoms are held together by the attraction between opposite charges Electrons are transferred completely from one atom to another and are not shared Lose of electron / gain of electron © McGraw Hill LLC 19 Types of Chemical Bonds: Ionic 2 Sodium has one electron in valence shell. Usually gives up an electron Chlorine has seven electrons in valence shell. Usually accepts an electron from another atom Ions—charged atoms from gaining or losing electrons Sodium has one more proton than electrons: now Na+. Chlorine has one more electron than protons: now Cl-. Ionic compounds often called salts. © McGraw Hill LLC 20 10  9/19/2023 Types of Chemical Bonds: Covalent Covalent bonding Two atoms share pair of electrons Two hydrogen atoms can share electrons to fill their outer shell—orbitals overlap. Structural formula—uses straight lines H-H One line indicates one pair of shared electrons. Molecular formula—simply shows number of atoms involved H2 © McGraw Hill LLC 21 Double Covalent Bonds Double covalent bonding: Two atoms share four electrons Double bonds are stronger than single bonds Access the text alternative for slide images. © McGraw Hill LLC 22 11  9/19/2023 Figure 2.8 Shapes of Covalently Bonded Molecules Access the text alternative for slide images. © McGraw Hill LLC 23 Chemical Formulas and Reactions 1 Reactants—molecules that participate in reactions at start Shown to the left of the arrow Products—molecules formed by reactions Shown to the right of the arrow S + O 2 → SO 2 2H 2O 2 → 2H 2O + O 2 Reactants Products © McGraw Hill LLC 24 12  9/19/2023 Chemical Formulas and Reactions 2 Equation is balanced if the same number of each type of atom occurs on both sides of the arrow. An overall equation for photosynthesis 6CO2 6H2O C6H12 O6 6O2 + → + carbon dioxide water glucose oxygen Molecular formula for glucose © McGraw Hill LLC 25 2.2 Water’s Importance to Life Life began in water. Single most important molecule on Earth All organisms are 70–90% water Water has unique properties that make it a life-supporting substance. Properties stem from the structure of the molecule. © McGraw Hill LLC 26 13  9/19/2023 Water’s Importance to Life: Structure Polar covalent bond Atoms do not share electrons equally. Oxygen is more electronegative than hydrogen. Electrons spend more time around the oxygen nucleus than the hydrogen nuclei. Oxygen end becomes slightly negative/hydrogens become slightly positive—NOT an ionic bond or ions Hydrogen bond—slightly positive hydrogen of one water molecule attracted to the slightly negative oxygen in another water molecule © McGraw Hill LLC 27 Figure 2.9 The Structure of Water Access the text alternative for slide images. © McGraw Hill LLC (photo): annedehaas/E+/Getty Images 28 14  9/19/2023 Properties of Water: Overview Properties of water Solvency Cohesion and adhesion High surface tension High heat capacity High heat of vaporization Varying density © McGraw Hill LLC 29 Properties of Water: Solvency Water is a solvent. A dissolving medium Water is the most common solvent in natural systems. Due to polarity and H-bonding, water dissolves many substances Hydrophilic—molecules attracted to water Hydrophobic—molecules not attracted to water Water causes NaCl to dissociate; ex. sugar to dissolve in coffee Dissociation: a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into other things such as atoms, ions, or radicals, usually in a reversible manner. The salt NaCl dissociates in water. Access the text alternative for slide images. © McGraw Hill LLC 30 15  9/19/2023 Properties of Water: Cohesion and Adhesion Cohesion Ability of water molecules to cling to each other due to hydrogen bonding, like water moving up a 100-foot pine tree, from the roots to the leaves Adhesion Ability of water molecules to cling to other polar surfaces, like a wet glass slide sticking to laboratory counter Allows water to be excellent transport system both inside and outside of living organisms Contributes to water transport in plants © McGraw Hill LLC 31 Figure 2.10 Cohesion and Adhesion of Water Molecules Access the text alternative for slide images. © McGraw Hill LLC (tree): Paul Davies/Alamy Stock Photo; (man): Asiaselects/Getty Images 32 16  9/19/2023 Properties of Water: High Surface Tension Water has a high surface tension. Water molecules at the surface cling more tightly to each other than to the air above. Mainly due to hydrogen bonding © McGraw Hill LLC Jan Miko/Shutterstock 33 Properties of Water: Heat Capacity and Heat of Vaporization Water has a high heat capacity. The many hydrogen bonds linking water molecules allow water to absorb heat without greatly changing its temperature. Temperature of water rises and falls slowly. Heat of vaporization Takes a great deal of energy to break H bonds for evaporation. Heat is dispelled as water evaporates. © McGraw Hill LLC 34 17  9/19/2023 Figure 2.11 Heat Capacity and Heat of Vaporization © McGraw Hill LLC (a): Jill Braaten/McGraw Hill; (b): Cultura Creative RF/Alamy Stock Photo 35 Properties of Water: Varying Density Ice is less dense than water. Unlike other substances, water expands as it freezes. Ice floats rather than sinks. It makes life possible in water. Ice acts as an insulator. © McGraw Hill LLC Jeff Vanuga/Getty Images 36 18  9/19/2023 Figure 2.12 Properties of Ice Access the text alternative for slide images. © McGraw Hill LLC 37 2.3 Acids and Bases Water dissociates into an equal number of hydrogen ions (H+ ) and hydroxide ions (OH− ) H–O–H ⎯⎯ ⎯→ ⎯ H+ + OH− water hydrogen ion hydroxide ion © McGraw Hill LLC 38 19  9/19/2023 Acidic Solutions (High Concentration) Lemon juice, vinegar, and coffee Acids release hydrogen ions (H+ ) or take up hydroxide ions (OH− ) HCl ⎯⎯ → H+ + Cl− hydrochloric acid hydrogen ion chloride ion © McGraw Hill LLC 39 Basic Solutions (Low Concentration) Milk of magnesia and ammonia Either take up hydrogen ions (H+ ) or release hydroxide ions (OH− ) NaOH ⎯⎯ → Na + + OH− sodium hydroxide sodium ion hydroxide ion © McGraw Hill LLC 40 20  9/19/2023 pH and pH Scale pH: Mathematical way to indicate the number of hydrogen [H+] ions in solution pH scale ranges from 0 (acidic) to 14 (basic) pH below 7 is acidic—more [H+ ] than [OH− ] pH above 7 is basic—more [OH− ] than [H+ ] + − pH of 7 is neutral— [H ] equal to [OH ] © McGraw Hill LLC 41 Figure 2.13 The pH Scale Access the text alternative for slide images. © McGraw Hill LLC 42 21  9/19/2023 Buffers and pH Buffers: Chemical or combination of chemicals that keeps pH within normal limits + − Resists pH change by taking up excess H or OH pH of blood is about 7.35–7.45 and is maintained by buffer Diseases such as congestive heart failure and diabetes can result in acidosis (body can’t buffer extra H+ ions); left untreated death can result. © McGraw Hill LLC 43 Because learning changes everything. ® www.mheducation.com © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 22