Chapter 2 RRR PDF

Because learning changes everything.® Chapter 2 The Nature of Molecules and the Properties of Water Understanding Biology Fourth Edition Kenneth A. Mason, Tod Duncan Jonathan B. Losos © McGraw Hill LL...

Because learning changes everything.® Chapter 2 The Nature of Molecules and the Properties of Water Understanding Biology Fourth Edition Kenneth A. Mason, Tod Duncan Jonathan B. Losos © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.  The Nature of Molecules and the Properties of Water Fuse/Getty Images © McGraw Hill, LLC 2  All Matter is Composed of Atoms Matter has mass and occupies space Matter is defined as any substance in the universe that has mass and occupies space. Because you have mass, you MATTER! All matter is composed of atoms Atoms are composed of subatomic particles © McGraw Hill, LLC 3  Atomic Structure Atoms are composed of three types of subatomic particles Protons Positively charged particles Located in the nucleus Neutrons Neutral particles Located in the nucleus Electrons Negatively charged particles Found in orbitals surrounding the nucleus © McGraw Hill, LLC 4  Figure 2.2 Access the text alternative for these images © McGraw Hill, LLC 5  Atomic number defines elements Number of protons equals number of electrons Atoms are electrically neutral Atomic number = number of protons Every atom of a particular element has the same number of protons Element Any substance that cannot be broken down to any other substance by ordinary chemical means © McGraw Hill, LLC 6  Atomic mass Mass or weight? Mass – refers to amount of substance Weight – refers to the force gravity exerts on a substance Sum of protons and neutrons is the atom’s atomic mass Each proton and neutron has a mass of approximately 1 Dalton © McGraw Hill, LLC 7  Electrons Negatively charged particles located in orbitals Neutral atoms have same number of electrons and protons Ions are charged particles – unbalanced Cation – more protons than electrons = net positive charge Anion – fewer protons than electrons = net negative charge Ex. Na+Cl- © McGraw Hill, LLC 8  Isotopes Atoms of a single element that possess different numbers of neutrons Note – atom will still have same # of protons. Radioactive isotopes are unstable and emit radiation as the nucleus breaks up Half-life – time it takes for one-half of the atoms in a sample to decay Ex. Carbon-14 Can be used to date fossils as it has 5730 year half-life. So after 5730 years, one gram of carbon-14 would now be 0.5g. © McGraw Hill, LLC 9  Figure 2.3 Access the text alternative for these images © McGraw Hill, LLC 10  Electron arrangement Key to the chemical behavior of an atom lies in the number and arrangement of its electrons in their orbitals Bohr model – electrons in discrete circular orbits Modern physics defines orbital as area around a nucleus where an electron is most likely to be found We can not pinpoint exact position of any electron at any given time. No orbital can contain more than two electrons © McGraw Hill, LLC 11  Figure 2.4 Access the text alternative for these images © McGraw Hill, LLC 12  Atomic energy levels Electrons have potential energy related to their position Electrons farther from nucleus have more energy Be careful not to confuse these two: Energy levels – drawn as rings to indicate an electron’s energy Orbitals – have a variety of three-dimensional shapes; indicate an electron’s most likely location © McGraw Hill, LLC 13  Figure 2.5 Access the text alternative for these images © McGraw Hill, LLC 14  Redox During some chemical reactions, electrons can be transferred from one atom to another Still retain the energy of their position in the atom Oxidation = loss of an electron Reduction = gain of an electron © McGraw Hill, LLC 15  Elements Periodic table displays elements according to valence electrons Valence electrons – number of electrons in outermost energy level Inert (nonreactive) elements have all eight electrons Octet rule – atoms tend to establish completely full outer energy levels © McGraw Hill, LLC 16  Periodic Table of the Elements Access the text alternative for these images © McGraw Hill, LLC 17  Figure 2.6b There are 90 naturally occurring elements Only 12 elements are found in living organisms in substantial amounts Four elements make up 96.3% of human body weight: C, H, O, N Organic molecules contain primarily C, H, O, N Some trace elements are very important Ex. iodine Access the text alternative for these images © McGraw Hill, LLC 18  Electron energy levels for helium and nitrogen Access the text alternative for these images © McGraw Hill, LLC 19  Chemical Bonds Molecules – groups of atoms held together in a stable association Compounds – molecules containing more than one type of element Atoms are held together in molecules or compounds by chemical bonds © McGraw Hill, LLC 20  Ionic bonds Formed by the attraction of oppositely charged ions by electrostatic force Ions form when the atom has a gain or loss of electrons Na atom loses an electron to become Cl atom gains an electron to become Opposite charges attract so that remain associated as an ionic compound Electrical attraction of water molecules can disrupt forces holding ions together © McGraw Hill, LLC 21  Figure 2.9 Access the text alternative for these images © McGraw Hill, LLC 22  Covalent bonds 1 Form when atoms share 2 or more valence electrons Results in no net charge, satisfies octet rule, no unpaired electrons Strength of covalent bond depends on the number of shared electrons Many biological compounds are composed of more than 2 atoms – may share electrons with 2 or more atoms © McGraw Hill, LLC 23  Covalent bonds 2 Access the text alternative for these images © McGraw Hill, LLC 24  Electronegativity Atom’s affinity for electrons Differences in electronegativity dictate how electrons are distributed in covalent bonds Nonpolar covalent bonds – equal sharing of electrons Polar covalent bonds – unequal sharing of electrons © McGraw Hill, LLC 25  Hydrogen bonds Electropositive hydrogen from one polar molecule is attracted to an electronegative atom that is often oxygen Attraction produces hydrogen bonds Each individual bond is weak and transitory Cumulative effects are enormous Responsible for many of water’s important physical properties © McGraw Hill, LLC 26  van de Waals Attraction Weak bond Non-directional attractive force called van der Waals forces Form when two atoms are very close to one another Antibodies recognize the shape of an invading organism with this bond © McGraw Hill, LLC 27  Chemical reactions 1 Chemical reactions involve the formation or breaking of chemical bonds Atoms shift from one molecule to another without any change in number or identity of atoms Reactants – original molecules Products – molecules resulting from reaction © McGraw Hill, LLC 28  Chemical reactions 2 Extent of chemical reaction influenced by Temperature Concentration of reactants and products Catalysts Many reactions are reversible © McGraw Hill, LLC 29  Water Life is inextricably tied to water Single most outstanding chemical property of water is its ability to form hydrogen bonds Weak chemical associations that form between the partially negative O atoms and the partially positive H atoms of two water molecules © McGraw Hill, LLC 30  Figure 2.10 Access the text alternative for these images © McGraw Hill, LLC 31  Polarity of water Within a water molecule, the bonds between oxygen and hydrogen are highly polar Oxygen is much more electronegative than Hydrogen Partial electrical charges develop Oxygen is partially negative Hydrogen is partially positive © McGraw Hill, LLC 32  Figure 2.11 Access the text alternative for these images © McGraw Hill, LLC 33  Figure 2.12 Hermann Eisenbeiss/Science Source Cohesion – water molecules stick to other water molecules by hydrogen bonding Surface tension due to hydrogen bonds © McGraw Hill, LLC 34  Figure 2.13 Adhesion – water molecules stick to other polar molecules by hydrogen bonding Access the text alternative for these images © McGraw Hill, LLC 35  Properties of water 1 TABLE 2.3 The Properties of Water Property Explanation Example of Benefit to Life Cohesion/Adhesion Hydrogen bonds cause water molecules to Leaves pull water upward from the be attracted to other polar or charged roots; seeds swell and germinate. species. High specific heat Hydrogen bonds absorb heat when they Water stabilizes the temperature of break and release heat when they form, organisms and the environment. minimizing temperature changes. High heat of Many hydrogen bonds must be broken for Evaporation of water cools body vaporization water to evaporate. surfaces. Lower density of ice Water molecules in an ice crystal are Because ice is less dense than water, spaced relatively far apart because of lakes do not freeze solid, allowing fish hydrogen bonding. and other life in lakes to survive the winter. Solubility Polar water molecules are attracted to Many kinds of molecules can move ions and polar compounds, making these freely in cells, permitting a diverse compounds soluble. array of chemical reactions. Hydrophobic Water repels hydrophobic compounds, Biological membranes have bilayer exclusion forcing them to associate together. structure with hydrophobic interior. © McGraw Hill, LLC 36  Properties of water 2 Water has a high specific heat A large amount of energy is required to change the temperature of water Water has a high heat of vaporization The evaporation of water from a surface causes cooling of that surface Solid water is less dense than liquid water Bodies of water freeze from the top down Because hydrogen bonds in ice are farther apart © McGraw Hill, LLC 37  Figure 2.14 Access the text alternative for these images © McGraw Hill, LLC 38  Properties of water 3 Water is a good solvent Water dissolves polar molecules and ions Water organizes nonpolar molecules Hydrophilic “water-loving” Hydrophobic “water-fearing” Water causes hydrophobic molecules to aggregate or assume specific shapes © McGraw Hill, LLC 39  Acids and bases Water can form ions (ionization) Pure water Considered to be neutral Neither acidic nor basic pH is the negative logarithm of hydrogen ion concentration of solution © McGraw Hill, LLC 40  Acids and Bases - pH Acid Any substance that dissociates in water to increase the (and lowers the pH) The stronger an acid is, the more hydrogen ions it produces and the lower its pH Base Substance that combines with dissolved in water, and thus lowers the (and raises the pH) © McGraw Hill, LLC 41  Figure 2.15 Access the text alternative for these images © McGraw Hill, LLC 42  Buffers Substance that resists changes in pH Act by Releasing hydrogen ions when a base is added Absorbing hydrogen ions when acid is added Overall effect of keeping relatively constant © McGraw Hill, LLC 43  Figure 2.16 Access the text alternative for these images © McGraw Hill, LLC 44  Biological buffers Most biological buffers consist of a pair of molecules, one an acid and one a base Access the text alternative for these images © McGraw Hill, LLC 45 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.