BIOLOGY 111 1st Edition Lecture 3 Outline of Last Lecture I Methods II Reasonings III Experimentation IV Scientific Theory V Overview of Chemistry and Physics Outline of Current Lecture I Continue Chemistry Review II Bonds III Chemical Reactions IV Properties of water Current Lecture continue chemistry covalent bonds form when atoms share pairs of valence electrons equal pairing between two atoms single ex hydrogen one bond formed by sharing electrons between two atoms double ex oxygen two bonds formed by sharing electrons between two atoms triple ex nitrogen three bonds formed by sharing electrons between two atoms non polar covalent bonds equal sharing of electrons b c each atom have same electronegativity tug of war polar covalent bonds unequal sharing of electrons b c different electronegativity between the two atoms common in water between hydrogen and oxygen higher affinity therefore oxygen pulls the hydrogens more than hydrogen pulls Oxygen is one of the most electronegative of all the elements attracting shared electrons more strongly electronegativity affinity for electrons the differences dictate location of electrons electrons are not always shared evenly between atoms some attract shared electrons more readily than others These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute partial positive push electrons away and negative pull electrons towards extreme differences cause the gain and loss of electrons between atoms by pulling them forming ionic bonds Ion a charged atom or molecule anion the atom that gains an electron cation the atom that loses an electron also applies to entire molecules that are electrically charged Ionic bond attraction between oppositely charged cations and anions atoms or ions can be formed even if there is no electron transfer from one to the other Ionic bonds vs covalent bonds ionic very strong in air vacuum but weak in aqueous solution covalent very strong in general Ionic compounds salts compounds formed by ionic bonds salts often occur in nature as crystals does not consist of molecules unlike a covalent compound not all salts have equal number of cations and anions Hydrogen bonds non covalent attraction between a hydrogen and an electronegative atom between polar molecules these are weak but important between two partially charged atoms H being partial in living cells the electronegative atom is usually oxygen for water or nitrogen for ammonia atoms Van der Waals interactions are individually weak and occur only when atoms and molecules are very close together causing momentary electrical asymmetry in molecules although they are very weak interactions there are so many that they overall make a huge impact very temporary causing temporary connection b c of temporary imbalance of charges temporary partial positive negative charges that attract for temporary interactions ex gecko holding onto a wall or DNA and same concept as applied to Velcro depicting chemical bonds use structural formula or lewis dot structure body organizes new molecules if doesn t recognize it it gets rid of it so drugs natural and synthetic made to mimic compounds already in the body so body can recognize it binds it and produces the desirable effect Chemical reactions making and breaking of chemical bonds leading to changes in the composition of matter we are given starting materials known as reactants through a reaction our reactant starting material is converted into product Chemical equilibrium the exact point at which reactions offset one another when the forward and reverse reaction rates are equal this does not mean reactants and products are equal in concentration but that they have stabilized at a particular ratio Chapter 3 Water life depends on the unusual properties of liquid water everything in the body occurs in aqueous liquid form where there is water there may be life surface of mars and earth each have sediment and similar composition current conditions of mars don t suggest life but suggest there may have been waters unusual properties emerge from molecular characteristics There are FOUR emergent properties of water 1 Cohesive stick to itself to hold itself together this is due to hydrogen bonding surface tension measure of difficulty in stretching breaking the surface of a liquid 2 Adhesive sticks to other molecules clinging of one molecule to another water drop to a leaf or to a spider web 3 Moderation of temperature by water water moderates air temperature by absorbing heat from warmer air and releasing stored heat to cooler air water resists temperature change and is able to release and absorb a lot of heat without changing its own temperature A Heat form of energy total kinetic energy and based on the volume ex ocean holds more heat than glass of water B Temperature measure of heat or energy average kinetic energy and does not depend on volume ex ocean and glass of water have the same temperature a Specific heat water resists temperature change water absorbs releases heat with little change to actual temperature helps to moderate coastal environments b evaporative cooling heat of vaporization amount of energy to convert liquid to gas 580 cal 1 gram at room temperature to evaporate hydrogen bonds must break as evaporates heat is removed evaporative cooling will be burnt more by steam than hot water itself 4 Expansion upon freezing instead of solidifying like most other materials water expands allows ice to float water is one of few substances that is less dense as a solid than as a liquid at temperatures above 4 degrees Celsius water behaves like other liquids expanding as it warms contracting as it cools most dense at 4 degrees Celsius between 4 and 0 degrees Celsius water expands as it freezes rather than contracting as it would if above 4 degrees Celsius Ice Hydrogen bonds are stable holds it together firmly liquid water hydrogen bonds break and reform less stable Water as a Solvent Water molecules b c of polarity make a really good solvent solution mixture of two or more substances solvent the dissolving agent aqueous solution when water acts as the solvent hydration shell the sphere of water molecules around each dissolved ions working from the outside towards the inside water eventually dissolves all the ions structures due to Polar bonds are hydrophilic water loving Non Polar bonds are hydrophobic water hating elements don t occur in the same