BCHM 30700 1st Edition Lecture 2 Outline of Last Lecture I Syllabus Outline of Current Lecture I Basic Chemistry A Definition of Valence Electrons II Water and its Properties A Definition of Electronegativity III Chemical Bonds A Dipole Movements B Hydrogen Bonds C Covalent Bonds IV Functional Groups Current Lecture Valence electrons are electrons in the outermost orbital of the atom Carbon has 4 valence electrons and can form 4 bonds Nitrogen has 5 valence electrons and can form 3 bonds Oxygen has 6 valence electrons and can form 2 bonds Hydrogen has 1 electron and can form a single bond Many interactions of these elements take place in an aqueous environment Water is solvent with unique properties It can form hydrogen bonds and has hydrophobic interactions Water forms a dipole due to a difference in electronegativity between the hydrogen and oxygen atoms that it is made from Electronegativity refers to how much an atom wants to retain or give up its electrons Some common electronegativity values are Fluorine which has the highest at 4 0 Oxygen 3 5 Nitrogen 3 0 Carbon 2 5 and Hydrogen 2 1 Electronegativity trends in the periodic table are as follows electronegativity increases going upwards and towards the right The geometry of water which is a bent shape also creates the dipole movement The oxygen atom in the middle of water has a higher electronegativity that the surrounding oxygen This causes the oxygen to pull electrons forming the bonds more towards itself The oxygen has a negative dipole movement on it due to the influx of electrons The partial loss of electrons creates a positive dipole movement for each hydrogen atom The 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 electrons are both being pulled the same way which creates an overall net dipole movement as well The bonds that form water are covalent bonds A covalent bond shares the pairs of electrons amongst the atoms It is the strongest type of biological bond and requires an input of energy to break Water can also form hydrogen bonds with other water molecules as well as dissolved hydrophilic substances The hydrogen bonds allow water to have a high boiling point making it a good solvent for polar molecules Hydrogen bonds help to stabilize the structure of many three dimensional molecules in nature Hydrogen bonds are a weaker type of bond Covalent bonds have around 400 KJ mol of energy while hydrogen bonds only have around 20 KJ mol There are certain functional groups that must be memorized for biochemistry Below is a list of the functional group formulas their names and the geometry of the central carbon atom CH4 Methane Tetrahedral RCH4 Methyl Tetrahedral RCH2R Methylene Tetrahedral RCH CHR Methene Planar RCHR OH Alcohol Tetrahedral RCH O Aldehyde Planar RCR O Ketone Planar RCX O Carboxylic Acid Planar
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