BCHM 3050 001 Essential Elements of Biochemistry Spring 2015 Dr Srikripa Chandrasekaran Dr Sri Lecture 2 1 9 2015 Human nature is like water It takes the shape of its container Wallace Stevens I Molecular structure of water A Larger oxygen atom has partial negative charge and hydrogen atoms have partial positive charges B On the periodic table elements on the left bond with elements on the right electronegative on the right side and electropositive on the left side opposite charges attract C The charge on hydrogen and oxygen the fact that they share electrons covalent bond are the 2 things that hold water together Bonds A Certain properties make one atom more likely to form a bond with II B Unnatural compounds can be created by just understanding these another specific atom different characteristics C Electronegativity how well an atom can attract an electron D Polar covalent nonpolar covalent and ionic are the 3 types of bonds that you need to know well i ii iii Polar covalent the electrons shared by the atoms spend a greater amount of time closer to the oxygen nucleus than the hydrogen nucleus unequal sharing of electrons Nonpolar covalent two atoms share a pair of electrons with each other equally these shared electrons glue two or more atoms together to form a molecule equally share electrons Ionic involves the electrostatic attraction between oppositely charged ions these ions represent atoms that have lost one or more electrons known as cations and atoms that have gained one or more electrons known as anions 1 III IV Non polar covalent bond A Example methane 1 carbon atom and 4 hydrogen atoms B The electrons are being shared equally 50 50 both atoms are equally invested C The center of the bond the electron cloud is equidistant from each atom each atom is equally invested in the bond Polar covalent bond A Bond between oxygen and hydrogen is polar B Water is a dipole because the positive and negative charges are separate C Water is a polar covalent bond 1 oxygen and 2 hydrogens the oxygen is more invested in the bond has more pull on the electrons V Non partially covalent bonding A Three most important non covalent bonds i ii iii Hydrogen bonds Ionic interactions electrostatic interactions Van der Waals forces B The electrons are not shared between the atoms in non covalent bonds VI Hydrogen bond A An electron deficient hydrogen of one water is attracted to the unshared electrons of water forming a hydrogen bond i Has electrostatic i e opposite charges and covalent i e electron sharing characteristics B Partial negative charge on the oxygen and a partial positive charge on the hydrogen hydrogen bonding C The property of hydrogen bonding keeps water together D Hydrogen bonds are formed between 2 water molecules connecting the oxygen of molecule 1 to a hydrogen of molecule 2 i Hydrogen bond is an intermolecular bond E Polar covalent bonds are formed within a single water molecule connecting each hydrogen of molecule 1 to the oxygen of molecule 1 i Polar covalent bond is an intramolecular bond F 4 hydrogen bonds formed by 1 water molecule Ionic Bond A Na sodium and Cl chlorine form an ionic bond Na has 1 valence electron Cl has 7 valence electrons 8 electrons are needed to fill each outer shell i Na sodium contributes 1 electron leaving it with a closed shell Cl chlorine gains 1 electron leaving it with a closed shell ii VII 2 iii Na has only that 1 electron in its outer shell so it can either give away that 1 electron or gain 7 electrons in order to have a full outer shell it is easier to give away 1 electron rather than gain 7 electrons so it is more inclined to give away its 1 valence electron B Mg magnesium and O oxygen form an ionic bond Mg has 2 valence electrons and O has 6 valence electrons i ii Mg contributes 2 electrons leaving it with a closed shell O gains 2 electrons leaving it with a closed shell C Ca calcium Cl chlorine and Cl chlorine form ionic bonds Ca contributes 2 electrons leaving it with a closed shell Cl 1 gains 1 electron leaving it with a closed shell Cl 2 gains 1 electron leaving it with a closed shell i ii iii D Elements on the right side of the periodic table accept electrons Elements on the left side of the periodic table give electrons Van der Waals Forces A Occur between neutral permanent and or induced dipoles B Three types i ii iii Dipole dipole interactions Dipole induced dipole interactions Induced dipole induced dipole interactions C Oxygen attracts electrons towards itself D Van der Waals forces interaction between dipoles not a hard and fast interaction it is between different molecules but it is really generated between dipoles interaction between 2 different dipoles the positive and negative charged dipoles attract Water is the ideal biological solvent A Hydrophilic molecules cell water structuring and sol gel transitions i ii Water can dissolve ionic and polar substances Shells of water molecules form around ions forming solvation spheres B Hydrophobic molecules cannot dissolve in water anything that does not have a charge does not like to dissolve in water but water still plays a role in packaging the molecule C Hydrophilic molecules can dissolve in water D Water adapts to a certain shape Cohesion A Strong hydrogen bonds are what allow water droplets to form and B Cohesion keeps the water molecules of a water droplet together to keep the droplets together form the droplet Adhesion A Adhesion allows water droplets to stick to spider webs and other surfaces Surface Tension A Based on hydrogen bonding a property of water 3 VIII IX X XI XII ii i ii B Surface tension is the tension at the surface of a body of water C The pull on the surface water molecules is stronger downwards and weaker upwards and this creates surface tension XIII Ice floats on water A Maximum number of hydrogen bonds form when water has frozen into ice i Open less dense structure XIV Water has a high melting and boiling point A Water s melting and boiling points are exceptionally high due to hydrogen bonding i Each water molecule can form four hydrogen bonds with other water molecules Extended network of hydrogen bonds B Water boils at 100 degrees Centigrade that is how much energy needed to break the strong hydrogen bonds XV Hydrophobic effect A Amphipathic molecules Contain both polar and nonpolar groups Amphipathic molecules form micelles when mixed with water due to hydrophobic effect a Important feature for the formation of cellular compartments In aqueous
View Full Document
Unlocking...