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Biology Chapter 2/3 Notes

by: Allie Muro

Biology Chapter 2/3 Notes Biology 114

Allie Muro
Principles of Biology
Dr. Stevan Marcus

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week of 1/25 chapter two continued and start of chapter 3
Principles of Biology
Dr. Stevan Marcus
Class Notes
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This page Class Notes was uploaded by Allie Muro on Sunday January 31, 2016. The Class Notes belongs to Biology 114 at University of Alabama - Tuscaloosa taught by Dr. Stevan Marcus in Spring 2016. Since its upload, it has received 7 views. For similar materials see Principles of Biology in Biology at University of Alabama - Tuscaloosa.


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Date Created: 01/31/16
Chapter 2 Valence electrons and chemical bonds Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms These interactions usually result in atoms staying close together held by attractions called chemical bonds Atoms with the same number of electrons in their valence shell have similar chemical reactivity The fewer valence electrons an atom holds the less stable it becomes and the more likely it is to react eg Na and Mg Elements in the same columns on the periodic table have same number of valence electrons 0 Hydrogen lithium sodium 9 all have 1 valence electron 0 Oxygen sulfur 9 all have 6 valence electrons Chemical Bonds Covalent bonds are strong bonds resulting from sharing of valence electrons by atoms 0 Non polar valence electrons shared equally by bonded atoms H2 0 Polar valance electrons not shared equally by bonded atoms H20 Ionic bonds are bonds resulting from loss and gain of electrons by bonded atoms eg NaCl strong but weaker than covalent bonds Hydrogen bonds weak bond formed between a hydrogen atom in a polar compound and an electronegative atom in another polar compound Van der Waals Force very weak bonds resulting from transient shifting of charges created by the constant movement of electrons Electronegativity Atoms in a molecule attract electrons to varying degrees Electronegativity is an atoms attraction for the electrons in a chemical bond An atoms electronegativity is affected by both its atomic number number of protons in its atoms and the distance at which its valence electrons reside from the charged nucleus The more electronegative an atom the more strongly it pulls electrons toward itself including shared electrons in covalent bonds Covalent Bonds A covalent bond is the sharing of a pair of valence electrons by two atoms In a covalent bond the shared electrons count as part of each atoms valence electron sheH Two hydrogen atoms can form a covalent bond by sharing their single valence electrons A molecule consists of 2 or more atoms held together by covalent bonds 0 A single bond is the sharing of 1 pair of valence electrons o A double bond is the sharing of 2 pairs of valence electrons o A triple bond is the sharing of 3 pairs of valence electrons Nonpolar Covalent Bonds In a nonpolar covalent bond the atoms are equally electronegative and share valence electrons equally eg H2 and 02 Polar Covalent Bonds One atom sis more electronegative and the atoms do not share valence electrons equaHy Unequal sharing of electrons causes a partial positive or partial negative charge for each atom or molecule Water H20 is an example of a polar molecule 0 Oxygen is one of the most electronegative elements and attracts shared electrons much more strongly than hydrogen 0 Electrons in a water molecule spend more time near an oxygen atom than a hydrogen atom 0 As a result the oxygen atom has a partial negative charge and each hydrogen atom has a partial positive charge Ionic Bonds Involve loss and gain of electrons the more electronegative atom actually strips a valence electron completely away from its partner An example is the transfer of an electron from sodium Na to chlorineCl which require only one electron to fill its valence shell After the transfer of an electron both atoms have charges A charged atom or molecule is called an ion 0 Cation Positively charged ion 0 Anion negatively charged ion An ionic bond is an attraction between an anion and a cation Chemical Formulas The notation used to represent atoms and bonding is called a structuralformula o HH This can be abbreviated further with a molecular formula 0 H2 A Lewis dot diagram shows valence electron distribution in an atom or molecule 0 HH Chapter 2 Van de Waals ForceInteractions Weak electrostatic attractions between molecules resulting from transient shortlived slight shifting of charges created by the constant movement of electrons Dependent on how much surface one molecule exposes to its neighbors Van der Waals interactions are the reason some large nonpolar molecules such as petroleum jellies stick together and why certain species of geckos can climb on sheer surfaces or even upside down Can be strong as between molecules of the thousands of hairlike setae of a Tokay geckos toe hairs and the surface of a wall Molecular shape and function A molecules shape is usually important to its function A molecules shape is determined by the positions of its atoms electron orbitals In a covalent bond the s and p orbitals may hybridize creating specific molecular shapes Molecular shape is crucial in biology because it determines how biological molecules specifically recognize and respond to one another Molecules with similar shapes can have similar biological effects The pain medication morphine binds to receptors in brain cells for endorphin neuropeptides that relieve pain and induce euphoria during times of stress exercise or excitement Chemical Reactions Making and breaking of chemical bonds 0 Starting molecules are called reactants 0 Final molecules are called products Chemical reactions involving biological molecules are referred to as biochemical reactions Biochemistry study of the chemical processes in living organisms Chapter 3 Water supports all life on earth Biological medium solvent for life as we know it Only common substance to exist in the natural environment in all 3 physical state of matter liquid solid gas Structure of water molecule is highly polar because oxygen atoms have much higher electronegativity than hydrogen atoms High polarity of water molecules allows them to interact with other polar or charged molecules 0 Including large macromolecules eg carbohydrates nucleic acids and proteins Water is a polar molecule The electrons of its polar covalent bonds spend more time near the oxygen atom than the hydrogen atoms 0 This property makes water a polar molecule with regard to distribution of its overall charge I Oxygen has a partial negative charge I Hydrogens have a partial positive charge Polarity of water molecules allows them to form hydrogen bonds with each other and with other polar compounds 1 water molecule can form up to 4 hydrogen bonds with other water molecules and other polar compounds hydrogen bonds are weak constantly broken and reformed properties of water that contribute to earths sustainability for life 4 properties facilitate an environment for life 0 cohesion and adhesion o ability to moderate temperature 0 expands upon freezing o versatility as a solvent for other polar and ionic compounds cohesion and adhesion cohesion a chemical attraction between particles of the same substance 0 hydrogen bonds hold water molecules together adhesion chemical attraction between different substances 0 water will adhere to other polar or charged substances such as the cell walls of plants cohesion and adhesion make it possible for water to be transported against gravity in plants water has a high surface tension surface tension measure of how difficult it is to stretch or break the surface of a liquid directly related to cohesion higher surface tension than most because water molecule form hydrogen bonds with other water molecules examples of surface tension in action 0 water walking insects 0 water globe above rim of a glass or on a coin moderation of temperature by water water has high specific heat 0 it can absorb or release a large amount of heat with only a slight change in tis own temperature high specific heat can be traced to hydrogen bonding o absorbs heat when hydrogen bonds are broken in warmer air 0 water releases heat when it forms hydrogen bonds cooler air high specific heat of water minimizes temperature fluctuation to within limits that permit life on earth evaporative cooling evaporation transformation from liquid to gas heat of vaporization heat of a liquid must absorb lg to be converted to gas as liquid evaporates its remaining surface cools a process called evaporative cooling 0 helps stabilize temperature in organism and bodies of water 0 allows plants and animals to cool themselves 0 sweating and panting allow excess heat to escape the body because water absorbs heat due to high SH 0 high humidity on hot days increases the discomfort from heat because the high concentration of water vapor inhibits the evaporation of sweat from the body water can freeze and solidify in ice each molecule of water is hydrogenbonded to 4 other water molecules in a a3 dimensional crystal each crystal is spacious so ice has fewer molecules than an equal volume of water in which hydrogen bonds are constantly breaking and reforming water is the solvent of life solution liquid that is a completely homogeneous mixture of substances solvent dissolving agent of a solution solute substance dissolved in a solution aqueous solution one in which water is the solvent water is a versatile solvent due to its polarity which allows it to form hydrogen bonds easily when an ionic compound is dissolved in water each ion is surrounded by a sphere of water molecules called a hydration cell


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