BIOLOGICAL SCIENCE. Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge. FIFTH EDITION Freeman Quillin Allison

Transcription

1 BIOLOGICAL SCIENCE FIFTH EDITION Freeman Quillin Allison 2 Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge

2 Roadmap 2 In this chapter you will learn that Chemistry is intimately linked to the evolution of life by reviewing How are atoms bonded together in molecules? and asking The structure of atoms, ions, and molecules 2.1 and asking How do chemical reactions occur? 2.3 then examining The unique properties of water 2.2 Current models for chemical evolution then examining Carbon: The most versatile atom on Earth

3 (a) Diagrams of atoms Electron Atoms are composed of positively charged particles neutral particles negatively charged particles Protons and neutrons are located in the Electrons are found in surrounding the nucleus Hydrogen Carbon Proton Neutron Nucleus (b) Most of an atom s volume is empty space. If an atom occupied the same volume as this stadium, the nucleus would be about the size of a pea

4 The Every different atom has a characteristic number of protons in the nucleus Atoms with the same atomic number Have the same chemical properties Belong to the same are Forms of an element with different numbers of neutrons The is The number of protons neutrons of the most common isotope

5 Figure 2.2 Mass number (number of protons + neutrons) Atomic number (number of protons)

6 Figure 2.3 Hydrogen Electron shell Nucleus The highlighted elements are the most abundant elements found in organisms Number of unpaired electrons = valence Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon Valence =

7 Unfilled electron orbitals allow formation of Are most stable when each electron orbital is filled Are substances held together by covalent bonds Each atom s unpaired valence electrons are shared by both nuclei to fill their orbitals Electrons are transferred from one atom to another

8 Electrons are not always shared equally An atom in a molecule with a high Holds electrons more tightly has a partial negative charge ( ) The other atom will have a partial positive charge ( Covalent bond ) Hydrogen atoms each have one unpaired electron H 2 molecule has two shared electrons

9 Differences in electronegativity dictate how electrons are distributed in covalent bonds Electrons are evenly shared between two atoms The bond is symmetrical Electrons are asymmetrically shared (a) Nonpolar covalent bond in hydrogen molecule Electrons are halfway between the two atoms, shared equally (b) Polar covalent bonds in water molecule Electrons are not shared equally (O is more electronegative than H), so partial charges exist on the O and H atoms

10 Ion -An atom or molecule that carries a charge Cation -An atom that loses an electron and becomes positively charged Anion -An atom that gains an electron and becomes negatively charged Ionic bond-the resulting attraction between oppositely charged ions (a) A sodium ion being formed Loss of electron (b) A chloride ion being formed Cation formation Sodium ion has positive charge (c) Table salt (NaCl) is a crystal composed of two ions. Cl Na + Gain of electron Anion formation Chloride ion has negative charge

11 Figure 2.8 (a) Single bonds Water H 2 O Ammonia NH 3 Methane CH 4 (b) Double bonds (c) Triple bonds Carbon dioxide CO 2 Molecular nitrogen N 2

12 occur when One substance is combined with another Atoms are rearranged in molecules Or small molecules combine to form larger molecules One substance is broken down into another substance Molecules are split into atoms or smaller molecules In most chemical reactions Chemical bonds are broken and new bonds form This event is called a coupled reaction

13 Life is based on water because water is a great The covalent bonds in water are polar, because oxygen has a greater electronegativity than hydrogen Oxygen has a partial negative charge ( ) Hydrogen has a partial positive charge ( )

14 atoms and molecules Are ions and polar molecules that stay in solution They stay in solution because of their interactions with water s partial charges makes it possible for almost any charged or polar molecule to dissolve in water molecules Are uncharged and nonpolar compounds They do not dissolve in water

15 is unique due to its structure Small size Bent shape Highly polar covalent bonds Overall polarity Binding between like molecules Binding to itself Results in high surface tension Binding between unlike molecules Binding to plastic or epithelial layers

16 Figure 2.15 (a) A meniscus forms where water meets a solid surface, as a result of two forces. Adhesion: Water molecules that adhere to the glass pull upward at the perimeter. Cohesion: Water molecules at the surface form hydrogen bonds with nearby water molecules and resist the upward pull of adhesion. (b) Water has high surface tension. Because of surface tension, light objects do not fall through the water s surface

17 Proton [hydrogen ion (H )] concentration is the basis of the ph scale ph expresses proton concentration in a solution The ph of pure water is 7 Acids have a ph of less than 7 Bases have a ph of greater than 7 In A proton donor (acid) transfers a proton to A proton acceptor (base) Neutral Basic Acidic Oven cleaner Household bleach Household ammonia Milk of magnesia Baking soda Seawater Human blood Pure water Milk Urine Black coffee Tomatoes Wine Vinegar, soft drinks, beer Lemon juice Stomach acid

18 The ph scale is logarithmic: Basic ph = log [H ] Greater H concentration more acidic Lower H concentration more basic/alkaline are compounds that minimize changes in ph Neutral Oven cleaner Household bleach Household ammonia Milk of magnesia Baking soda Seawater Human blood Pure water Milk Urine Black coffee Tomatoes Wine Vinegar, soft drinks, beer Lemon juice Stomach acid Acidic

19 have and For example: CO 2 (g) H 2 O(l) occurs H 2 CO 3 (aq) When the forward and reverse reactions proceed at the same rate The quantities of reactants and products remain constant must absorb heat to proceed release heat

20 is the capacity to do work or supply heat This capacity exists in one of two ways: As a stored potential As an active motion Stored energy An object s position determines its ability to store energy, for example Electrons in an outer shell (farther from the charged nucleus) have more potential energy than do electrons in an inner shell

21 The or Is energy of movement Is measured as temperature If an object has a low temperature: Its molecules are moving slowly We perceive this as cold If an object has a high temperature: Its molecules are moving rapidly We perceive this as hot

22 Heat is the thermal energy transferred between objects of different temperatures The first law of thermodynamics Energy is conserved It cannot be created or destroyed It can be transferred or transformed The second law of thermodynamics Entropy always increases Chemical reactions result in products with Entropy (S) Less ordered energy Less usable energy The amount of disorder in a group of molecules Physical and chemical processes proceed in the direction that results in lower potential energy and increased disorder

23 Figure 2.24 (a) Carbons linked in a chain (b) Carbons linked in a ring C 6 H 12 O 6 Glucose C 8 H 18 Octane