Exam 1 Chapter 2 The Chemical Context of Life The structure of an atom The atomic nucleus this contains our neutrons and our protons The electron cloud surrounds the nucleus and contains our electrons o Atomic number this is the number of protons This number NEVER changes meaning the number of protons in every element is constant o Atomic mass atomic weight the sum of the mass of our neutrons and our protons We measure this in DALTONS o Isotopes two atoms of the same element with different numbers of neutrons in the nucleus An example we covered in class was Carbon 12 vs the isotope Carbon 14 Arrangement of electron shells o Valence electrons o Relative potential energy of electrons Types of bonds and reasoning why Electronegativity electrons are not always shared equally between two atoms of a covalent bond o High E negative atoms have a stronger attraction to electrons and pull shared electrons closer to their nucleus o This is an atoms PULL on electrons o I e Hydrogen is low and Oxygen Nitrogen are high Covalent bonds o Which atoms form covalent bonds with each other Atoms that share pairs of their valence electrons and then can gain stability This is between a non metal and a non metal o Polar vs Non polar Polar Covalent electrons are shared unequally Partial charges are created in the molecule b c one atom is much more electronegative than the other Non Polar Covalent electrons are shared equally Similar electronegativity o Single vs Double covalent bonds Single two electrons are shared between two atoms depicted as a single line between two atoms This is the most stable because there is a lower level of reactivity Double when two atoms share four electrons two pairs depicted as two Ionic bonds lines between the atoms o Which atoms form ionic bonds with each other Exam 1 o Atoms that have opposite charges so one ion loses an electron known as a positively charged cation and one atom gains an electron known as a negatively charged anion Weak interactions o Hydrogen bonds forms when a Hydrogen atom covalently bonded to one electronegative atoms is also attracted to another electronegative atoms Chemical Equilibrium This state is reached when the forward and reverse reactions occur at the SAME Rate The relative concentrations of reactants and products do not change Designated by a double sided arrow Ex H2 O2 2H2O Exam 1 Chapter 3 Water and Life Hydrogen Bonds between Water atoms this is caused because water is a polar molecule with TWO polar covalent bonds within it therefore the opposite ends have opposite charges This leads to molecules being held together by hydrogen bonds Hydrogen Bonds are responsible for the characteristics of water Cohesion Temperature moderation Lower density as a solid and Properties and versatility as a Solvent These properties arise because of the Resistance to change in temperature o Storage and Release of Heat Energy Water absorbs heat from warmer air and releases stored heat to cooler air Water can absorb or release a large amount of heat with only a slight change in its own temperature Attributed to a HIGH Specific Heat o Nature of Specific Heat and Calories Definitions Calorie cal amount of heat required to raise the temperature of 1g of water by 1 C Calories on food packages are actually kilocalories kcal where 1kcal 1 000 cal Specific Heat of a substance is the amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1 C o Specific heat of water 1 cal g C o This is why water resists changing it s temperature b c of a high specific heat Heat of Vaporization the heat a liquid must absorb for 1g to be Evaporative Cooling as a liquid evaporates it s remaining surface converted to gas cools Colloid a stable suspension of fine particles in a liquid Individual molecules are too large to go into full suspension Reaction Rate this is dependent on concentration of each molecule solute Hydrogen Bonds Heat is absorbed when hydrogen bonds BREAK Breaking H bonds requires energy An increased Temperature leads to an increased distance between water molecules This leads to LESS H bonds Heat is released when hydrogen bonds FORM Forming H bonds releases Energy A decreased temperature decreases the distance between water molecules This leads to MORE H bonds Therefore it s logical to assume that more heat is req d to raise the temperature of water because of these hydrogen bonds Ability of Polarized Hydrophillic molecules to dissolve in water o Hydrophillic water loving o We can have hydrophilic molecules dissolve in water through hydrogen bonds Inability of non polar Hydrophobic molecules to dissolve in water Exam 1 o Hydrophobic water fearing o i e oil molecules because they have relatively non polar bonds Molarity and its relation to Molecular Mass Molecular mass the sum of all mass of all atoms in a molecule 1 mol 6 02 1023 molecules 6 02 1023 daltons 1g Molarity M moles L of solution Chemical basis for acids and bases Concentration of H and OH ions o Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed o In pure water these concentrations are equal What molecules can change either the H or OH concentration of a solution o Solutes called acids and bases modify the concentrations of H and OH o Acid any substance increasing the H o Base any substance reducing the OH The pH Scale Potential of Hydrogen The nature of a logarithmic scale H OH 10 14 pH log H i e H 10 7 so pH 7 7 Exam 1 Chapter 4 Carbon Molecular Diversity of Life Understand the basic properties of the carbon atom and why it makes the perfect basis for large complex biological molecules With it s electron configuration Carbon is able to form 4 covalent bonds and share all of its electrons this provides the backbone for a diverse array of molecules Living organisms consist mostly of Carbon based compounds No other atom can form as large complex and diverse molecules Proteins Nucleic Acids Carbs and Lipids Two definitions discussed in class o Vitalism the idea that organic compounds are distinct and can only arise from within a living organism outside and inside cell processes are different o Mechanism the view that all natural phenomena are governed by physical and chemical laws outside and inside cell processes are the same Stanley Miller designed an experiment to address this and discovered Abiotic Synthesis of Formaldehyde Hydrogen Cyanide AAs and HCs So organic molecules can be
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