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BU BIOL 118 - Lecture 150130

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Lecture 150130Electronegativity- a measure of the ability of an atom to attract electrons from an atom it is bonded to determined based on 1. Number of protons2. Distance between nucleus and the valence shell3. O and N are more electronegative than C and HAtoms with a high electronegativity will hold the electrons more tightly than that with a lower electronegativity and have a partial negative charge whereas the other atom in the molecule will have a partial positive chargeThe upper left corner has the highest electronegativity fluorine is the most likely to bond with anything but oxygen bonds a lot too bottom left corner of periodic table has lowest electronegativityChemical bonds- differences in electronegativity dictate how electrons are distributed in covalentbonds1. Nonpolar covalent bond- electrons are evenly shared between two atoms and the bond is symmetrical2. Polar covalent bond- electrons are asymmetrically shared waterr-O-H -> H-O is a covalent bond r-H is a radical bond; could be anything or nothing the electron in the OH bond will stay with the O so the H will be positive a little bit δ+ the partial charges are why water has the bend in the molecule: electrons hate each other and want to be as far away as possible and there’s 3 pairs on the outer electron shell and the angle where there’s maximum distance between all electrons is 120 the δ+ and δ- can make very weak bonds called hydrogen bondsoxygen gas molecules are non-polar because the electronegativity of oxygen is in fact the same as the electronegativity of oxygen so the atoms have even pull and the electrons are shared evenlysome pictures of bonding from the bookIonic bonds- an atom or molecule that carries a charge is called an ion 1. Cation- loses electron gains positive charge2. Anion- gains electron becomes negatively chargedThey form bonds like the way magnets do negative attracts positiveSome pictures of a salt crystalElectron sharing continuum- the degree to which electrons are shared in chemical bonds forms a continuum from equal sharing in nonpolar covalent bonds to unequal sharing in polar covalent bonds to the transfer of electrons in ionic bondsPicture from the bookProperties of water- called the universal solvent life is based on water because water is a great solvent the covalent bonds in water are polarIons and polar molecules dissolve in water because of the partial charges they are hydrophilic water won’t dissolve lipids or non-polar stuff because they don’t interact with water. LIKES DISSOLVE LIKES which is why you need soap because it is both polar and non-polar and can dissolve anything including your skin if given enough timeStructure and properties- Water is unique due to its small size bent shape highly polar covalent bonds and overall polarity1. Cohesive- it sticks to itself- why water makes spherical droplets2. Adhesive- it sticks to other stuff3. Denser as a liquid than a solid- ice floats due to its open crystal structure4. Able to absorb large amounts of energy- it takes a ~4 calories to raise a gram of water onedegree- it has a high specific heatCarbon- carbon is the most versatile atom on earth. Because it has a valence of four carbon can form many covalent bonds- Carbon containing molecules can form an almost limitless array of molecular shapes withdifferent combinations of single and double bonds- The formation of carbon carbon bonds was an important event in chemical evolution because we are carbon based life forms- Things usually get named after their number of carbons –octane -> C8H18 hexane -> C6H14Functional groups- the carbon atoms in an organic molecule furnish the skeleton that gives the molecule its overall shape- Amino groups- negative charge; attract protons/protium NH3+- Carbonyl- link molecules into larger compounds C=O- Carboxyl- releases a proton; negative charge COOH/COO-- Hydroxyl groups- polar group and act as weak acids OH- Phosphate groups- have two negative charges PO4- Sulfhydryl groups- link together via disulfide bonds SHQUESTION: why do most polar covalent bonds involve nitrogen or oxygen? Because they are the most electronegative so any bond with them will probably not have equal sharing of electronsQUESTION predict what part of water molecules would interact with amino carboxyl and hydroxyl groups-> amino: the oxygen part is negative NH3+ is positive carboxyl: the H parts are positive and COOH is kinda negative hydroxyl: negative charge will like the H parts that are


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BU BIOL 118 - Lecture 150130

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