GS106 Chemical Bonds and Chemistry of Water c wou gs106 sp2002 chem wpd I Introduction A Hierarchy of chemical substances 1 atoms of elements smallest particles of matter with unique physical and chemical properties that still retain the properties of matter a e g hydrogen oxygen 2 Isotopes of elements a isotopes of a given element are represented by atoms with the same atomic number but different numbers of neutrons b e g Oxygen Isotopes 18 1 O less common variety of oxygen 8 protons 10 neutrons 16 2 O most common variety of oxygen 8 protons 8 neutrons 3 Ion charged atomic particle a atoms that gain or lose electrons result in net positive or negative charge 1 the number of protons remains unchanged but the number of electrons changes to result in net charge b cation positively charged atoms that lose electrons 1 e g H 1 hydrogen that has lost 1 electron c anion negatively charged atoms that gain electrons 1 e g 16O 2 Oxygen 16 ion that has gained 2 electrons 8 protons d Complex cations and anions ions comprised of more than 1 element compound ions 1 e g HCO3 bicarbonate anion Common Dissolved Ions Found in Natural Waters Na Sr 2 Br sodium strontium bromide Mg 2 ClFe 2 iron magnesium Ca 2 calcium chloride SO4 2 sulfate Fe 3 iron K potassium HCO3 bicarbonate 4 molecules of 1 or more atoms of elements a e g water molecule H2O b e g 2 H 1 O 2 H20 5 compounds of elements bonded together a physical and chemical properties of compounds differ from that of the constituent atoms of elements b e g sodium chloride NaCl 6 mixtures of unbonded elements and compounds a e g mixture of salt and sugar 57 B Chemical Bonds 1 Atomic Forces that hold atoms together in molecules or ions in crystals a b c atoms form bonds with other atoms to form compounds all physical properties of chemical compounds are controlled by the atomic arrangement and bonding characteristics of the component atoms bonding between atoms is largely controlled by the electron configuration of the outermost valence electron shell 1 bond style is controlled by octet rule tendency for atoms to attain a stable 8 electron configuration in the outermost valence shell a exception to octet rule hydrogen tendency towards 2 electrons in outermost shell 2 Note for the Noble Gases on the far right column of the periodic chart the outmost valence shell is full thus the noble gases are intert non reactive example of chemical bonding and octet rule Na 1 Cl 1 NaCl e g NaCl Na has an atomic no of 11 and thus contains 11 electrons around the nucleus 2 in first energy level 8 in second energy level and 1 in valence or outer energy level Cl has an atomic no of 17 and thus 17 electrons about its nucleus 2 in first level 8 in second level 7 in outer level Thus Na needs to lose 1 electron from outer shell to obtain stable configuration and Cl needs to gain 1 electron in outer shell to obtain stable configuration tendancy for ionic bonding to form NaCl 2 Lewis Electron Dot Models of Atoms a electron dot models represent the configuration of the valence electron shell or outermost shell 1 outershell electrons are filled 1 by 1 around the nucleus and then paired to form a square dance set In Class Exercise Using the periodic chart write the lewis electron dot models for the following atoms K H C Si Ca 58 F O b representing chemical reactions with dot models In Class Exercise write the electron dot models for H and Cl show the dot model reaction that froms hydrochloric acid H Cl HCl Write the electron dot model reaction of Mg O to form MgO Write the electron dot model reaction for 2 K O to form K20 Write a chemical reaction calcium choride to form calcim chloride 3 C Bond Types a ionic bonds transfer of electrons between atoms b covalent bonds sharing of electrons between atoms c Metallic bonding extreme case of electron sharing in which electrons move freely from atom to atom Metallic bonding accounts fo the high electrical conductivity of metals and other special properties Aqueous Solutions 1 water based solutions homogeneous mixture of two or more substances a homogeneous mixing throughout with individual ions separated apart from others 2 solute the substance being dissolved 3 solvent the substance doing the dissolving a water is associated with a high degree of dissolving power 4 e g saline solution adding salt to water a water dipolar molecule with and ends to the molecule b a sheath of hydration surrounds the sodium and chlorine atoms to force them apart electrostatically 59 NaCl H2O Na Cl H2O D Measuring concentrations of solutes in aqueous solutions 1 concentration measurement of the quantity of solute in a given quantity of solvent or solution a Mass Percent mass solute total mass solution 100 E g if 5 g of NaCl is dissolved in 95 g of water what is the mass percent of sodium chloride in the solution conversion factors for mass 1 gram 1000 mg 1 kg 1000 g 1 gram 1 000 000 micrograms 1 b percent parts per hundred Parts per Thousand o oo grams of solute liter of water Determine the concentration in ppt for a solution of 200 gram dissolved in 2 liters of water Determine the concentration in ppt for a solution of 2000 mg dissolved in 1 liter of water c Parts per Million milligrams of solute liter of water Determine the concentration in ppm for a solution 20 mg of salt per liter of water What about 20 kg of salt per liter of water 60 d Parts per Billion micrograms of solute liter of water Determine the concentration in ppb for a solution of 200 micrograms of salt dissolved in 3 liters of water Determine the concentration in ppb for a solution 200 grams of salt dissolved in 4 liters of water e Molarity amount of solute in moles volume of solution in liters 1 Mole the amount of a substance that contains exactly the number of elementary entities as there are in carbon 12 atoms in exactly 12 g of carbon 12 a 1 mol 12C 6 022 x 1023 12 1 mol 16O 6 022 x 1023 16 Avagadro s number a constant the number of carbon 12 atoms contained in 12 g of carbon C atoms 12 0 gram the atomic mass of 1 atom of 12C O atoms 15 99 grams the atomic mass of 1 atom of 16O 1 mol of NaCl 6 022 x 1023 NaCl molecules atomic mass of Na atomic mass of Cl 23 35 58 grams the formula weight of 1 molecule of NaCl Question how many atoms are contained in 1 mole of chlorine 35 What is the mass of 1 mole of chlorine 35 Question if you had 24 grams of 12C how many moles would you have Question if you had 48 grams of 16O how many moles would …
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