CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 1 IN OUR PREVIOUS LECTURE WE WERE LOOKING AT HOW THINGS CHEMICALLY BOND NOW.

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1 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 1 CHM 105/106 Program 27: Unit 3 Lecture 10 IN OUR PREVIOUS LECTURE WE WERE LOOKING AT HOW THINGS CHEMICALLY BOND NOW. WE VE TALKED ABOUT THE ELECTRON STRUCTURE OF THE ATOM AND HOW THAT IS GOING TO BE USED AS A TOOL TO UNDERSTAND CHEMICAL BONDING AND WE NOTED THAT THE MOST NON-REACTIVE ELEMENTS ARE THOSE CALLED THE NOBLE GASSES WHICH ARE IN THE LAST COLUMN OF THE PERIODIC TABLE AND THEY HAVE THE UNIQUE STRUCTURE THAT THEY HAVE EIGHT ELECTRONS IN THEIR OUTERMOST ENERGY POSITION IN THE S AND P LEVEL. SO THE S AND P LEVEL OF THE HIGHEST QUANTUM NUMBER IS FILLED. REMEMBER THAT WE HAVE 1S ORBITAL AND 3P ORBITAL SO WE HAVE 4 ORBITALS IN THE S AND P AND EACH CAN HOLD TWO. THIS OCTET, THIS EIGHT ELECTRON SITUATION IS APPARENTLY A VERY ENERGY-STABLE CONDITION FOR THEN ELEMENTS FOR ATOMS TO ACHIEVE THEN IN CHEMICAL BONDING, AND SO WE SAID THAT THE DRIVING FORCE THEN IN CHEMICAL BONDING APPEARS TO BE THE TENDENCY TO ACHIEVE AN OCTET OF ELECTRONS. OR, IN OTHER WORDS, TO BECOME LIKE A NOBLE GAS OR WE SAY NOBLE GAS-LIKE ELECTRON STRUCTURE. WE FURTHER WENT ON AND SAID THAT WE CAN LOOK AT INDIVIDUAL ELECTRON DOT PICTURES FOR EACH OF THE ATOMS TO SEE HOW MANY VALENCE ELECTRONS THAT IT HAS AND THIS OF COURSE IS DETERMINES BY ITS LOCATION IN THE PERIODIC CHART. FOR INSTANCE, IF I WERE TO TAKE ELEMENT 15, PHOSPHORUS, AND I LOCATE IT IN THE PERIODIC TABLE I NOTE THAT IT IS UNDER THE COLUMN NUMBER FIVE IN THE P BLOCK, AND REMEMBER THAT ONLY S AND P ELECTRONS ARE VALENCE ELECTRONS. SO ELEMENTS IN THIS COLUMN HERE, THIS FAMILY OF NITROGEN, PHOSPHORUS, ARSENIC, ANTIMONY, AND BISMUTH ALL HAVE FIVE VALENCE ELECTRONS. THEY WOULD HAVE THE 2S AND THEN FOR PHOSPHORUS WE D BE 1, 2, 3 POSITIONS OVER 3P. SO IT HAS AN S 2 P 3 STRUCTURE. SO IT HAS FIVE VALENCE ELECTRONS, AND WE CAN SHOW THOSE FIVE VALENCE ELECTRONS THEN BY USING AN ELECTRON DOT PICTURE. SO WE WOULD SHOW TWO OF THEM AS PAIRED AND THREE SINGLES TO SHOW THE STRUCTURE THEN FOR THE PHOSPHORUS ATOM, AND WE SAID THEN THAT LOOKING AT THIS WE MIGHT SUSPECT THAT WHAT PHOSPHORUS WOULD WANT TO DO IS SOMEHOW GAIN THREE ADDITIONAL ELECTRONS. WE LL JUST USE X S

2 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 2 IT DOESN T MEAN THAT ELECTRONS ARE DIFFERENT, BUT TO GAIN THREE ELECTRONS, AND IT CAN DO THIS EITHER BY GIVE AND TAKE PROCESS. AND IF THIS OCCURS, IF IT S A GIVE AND TAKE, IN OTHER WORDS PHOSPHORUS IS GOING TO TAKE ELECTRONS, SOMETHING NEEDS TO GIVE ELECTRONS, THIS IS REFERRED TO AS IONIC BONDING BECAUSE WHAT HAPPENS WHEN THINGS GIVE OR TAKE ELECTRONS IS THEY NO LONGER REMAIN NEUTRAL ATOMS BUT BECOME IONS, AND IT S THE IONS THAT ARE THEN ATTRACTED TO EACH OTHER, OPPOSITE CHARGED PARTICLES THAT CREATES THE BONDING FORCE. THE BONDING FORCE IN IONIC BONDING IS ELECTROSTATIC THAT S WHAT S HOLDING THE PARTICLES TOGETHER, OPPOSITE ATTRACTION FORCES. BUT ALSO, IT MAY BE POSSIBLE THAT THE PHOSPHORUS OR WHATEVER ATOM IT IS THAT WE RE LOOKING AT MAY ACTUALLY OBTAIN THIS OCTET OF ELECTRONS THROUGH A SHARING PROCESS AND WE LL BE LOOKING AT THE SHARING PROCESS A LITTLE BIT LATER TODAY. SO EITHER BY GIVE AND TAKE OR BY SHARING PROCESS THEN AN ATOM TRIES TO ACHIEVE THIS OCTET, THIS NOBLE GAS-LIKE ELECTRON STRUCTURE. LET S FOCUS HERE QUICKLY FIRST OF ALL THEN ON A FEW EXAMPLES OF SOME IONIC BONDING AND WE LL START BY LOOKING AT THE REACTION BETWEEN CESIUM AND BROMINE. NOW, AGAIN IF WE LOOK AT THE PERIODIC TABLE AND LOCATE THE TWO ELEMENTS WE SEE THAT CESIUM, ELEMENT NUMBER 55 IS IN THE FIRST COLUMN INDICATING IT HAS ONE VALENCE ELECTRON. WE GO OVER HERE TO BROMINE AND WE SEE BROMINE IS IN THIS SEVENTH COLUMN SO THAT IT HAS SEVEN VALENCE ELECTRONS, AND SO THAT S WHAT WE VE SHOWN UP HERE IN THE DRAWING THEN CESIUM WITH ONE AND BROMINE WITH SEVEN. NOW, CESIUM, IN ORDER TO BECOME LIKE THEN LET S SAY RADON, WOULD HAVE TO GAIN SEVEN MORE VALENCE ELECTRONS, NOT LIKELY TO OCCUR. BUT IF CESIUM WERE TO LOSE ONE ELECTRON, IT HAS 55, IF IT LOSES ONE IT WILL HAVE 54 AND WHAT HAS AN ELECTRON STRUCTURE WITH 54 ELECTRONS? XENON HAS A STRUCTURE OF 54 ELECTRONS, MEANING THAT CESIUM NOW BECOMES LIKE XENON BY GIVING UP THAT ELECTRON. SO WE CAN SHOW HERE, WE HAVE, WELL AND THEN LOOKING AT BROMINE I GUESS WE SHOULD ALSO MENTION, BROMINE HAS SEVEN AND SO IN ORDER FOR IT TO BECOME LIKE A NOBLE GAS WHICH WOULD BE KRYPTON IT NEEDS TO GAIN ONE ELECTRON. SO CESIUM DONATES ITS ELECTRON, GIVES IT TO THE BROMINE. NOW WHEN THIS OCCURS,

3 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 3 WHAT WE ARE GOING TO PRODUCE THEN IS WE RE GOING TO PRODUCE A CESIUM WITH A +1 CHARGE, SO WE RE GOING TO PRODUCE A POSITIVE ION AND WE RE GOING TO PRODUCE A BROMINE WITH A 1 CHARGE AND THEREFORE THESE TWO ARE NOW HELD TOGETHER BY OPPOSITE CHARGES BY THE ELECTROSTATIC FORCE. THAT S WHAT WE RE TALKING ABOUT IN IONIC BONDING, ELECTROSTATIC ACTION IS WHAT S HOLDING THIS TOGETHER. ACTUALLY THEN IN MAKING UP A COMPOUND WHAT WE WOULD FIND IF WE LOOKED AT A LITTLE SOLID CHUNK OF CESIUM BROMIDE WE COULD SEE SOMETHING THAT LOOKED LIKE THIS, CESIUM AND THEN A BROMINE AND THEN A CESIUM AND THEN A BROMINE AND THEN A BROMINE AND A CESIUM AND A BROMINE AND A CESIUM AND CESIUM AND A BROMINE ET CETERA AS WE GO ALONG THEN MAKING UP THE SOLID. BUT WHAT I WANT TO STRESS HERE IS THAT THERE IS NO INDIVIDUAL MOLECULE. WE CAN T SAY THAT THESE TWO BELONG TOGETHER OR THAT THESE TWO BELONG TOGETHER. WE DON T KNOW WHICH TWO BELONG TOGETHER BUT WE DO KNOW THAT WE HAVE A 1 TO 1 COMBINATION. AS A MATTER OF FACT, YOU SEE WE TALKED ABOUT THE LAW OF DEFINITE COMPOSITION. THE REASON THAT CESIUM BROMIDE, THE COMPOUND INVOLVING CESIUM AND BROMINE WILL ALWAYS BE THE CHEMICAL FORMULA. AS A MATTER OF FACT, WE WOULD JUST WRITE IT IN CSBR. THE REASON THAT THAT CHEMICAL HAS A FORMULA CSBR IS THAT S THE ONLY WAY ELECTRONICALLY THOSE TWO CAN GET TOGETHER. IT CAN T GET TOGETHER 2 TO 1 OR 3 TO 1 OR 2 TO 2. IT S ONLY GOING TO COMBINE 1 TO 1 BECAUSE OF THE ELECTRON STRUCTURE. THAT S WHY WE LOOKED AT THE ELECTRON STRUCTURE. IT A LLOWS US THEN TO UNDERSTAND WHY WE HAVE THIS LAW OF DEFINITE COMPOSITION, WHY THERE S ONLY ONE WAY THAT THESE ELEMENTS COMBINE. IT S NOT A HAPHAZARD THING, IT IS BASED ON THEIR ELECTRON STRUCTURES. NOW, A COMMON COMPOUND THAT YOU RE ALSO FAMILIAR WITH IS TABLE SALT, SODIUM CHLORIDE. SODIUM CHLORIDE IS AN IONIC COMPOUND IN WHICH SODIUM HAS GIVEN UP AN ELECTRON TO A CHLORINE, AND WE MAKE A PLUS/MINUS ION, AND THEY WOULD MAKE UP A BLOCK OF SOLID MADE UP OF LITTLE IONS IN THAT SOLID, THAT PIECE OF SALT THAT WE RE LOOKING AT. AGAIN, SODIUM CHLORIDE, SODIUM S IN THE FIRST COLUMN, ONE ELECTRON. CHLORINE IN THE SEVENTH, SEVEN ELECTRONS, AND SO THE ONLY WAY SODIUM AND CHLORINE CAN COMBINE

4 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 4 ARE 1 TO 1 BECAUSE OF THE ELECTRON STRUCTURE. ALRIGHT, NOW WHAT TYPE OF COMPOUNDS, OR I SHOULDSAY WHAT TYPE OF ELEMENTS ARE INVOLVED IN IONIC BONDING? WELL TYPICALLY ANY OF THE METALS OF THIS SIDE OF THE CHART, THE 1A AND THE 2A ESPECIALLY COMBINING WITH ANY OF THE NON-METALS, REMEMBER THIS IS THE DIVIDING LINE HERE. ANY OF THE NON-METALS, METALS FROM THIS SIDE AND NON-METALS ARE GOING TO TYPICALLY COMBINE IN AN IONIC FASHION. SO WHEN I LOOK AT A CHEMICAL FORMULA I CAN MAKE SOME PREDICTION WHETHER OR NOT I WOULD EXPECT THIS TO BE AN IONIC BOND, AN IONIC COMPOUND OR THEN A COVALENT OR SHARING COMPOUND THAT WE LL TALK ABOUT IN A LITTLE BIT. LET S LOOK AT ANOTHER EXAMPLE HERE, LET S TAKE AN ELEMENT THIS TIME OUT OF THE SECOND COLUMN UNDER THE 2A UP THERE ON THE CHART, AND LET S USE STRONTIUM. AND SO STRONTIUM NOW HAS TWO VALENCE ELECTRONS. LET S COMBINE IT WITH THE NON-METAL, SULFUR, AND SULFUR IS OVER HERE UNDER THE SIXTH COLUMN AND SO IT WOULD HAVE THEN SIX VALENCE ELECTRONS. AND SO HOW DOES STRONTIUM AND SULFUR GET TOGETHER? WELL, AGAIN IF STRONTIUM WERE TO GIVE UP ITS ELECTRON TO THE SULFUR AND GIVE UP ANOTHER ONE TO THE SULFUR, SEE THE SULFUR HAS ONLY SIX SO IT CAN TAKE ON TWO MORE. WE WOULD END UP WITH STRONTIUM NOW WHICH IS ATOMIC NUMBER 38 TO START WITH. IF IT LOSES TWO ELECTRONS IT S GOING TO HAVE AN ELECTRON STRUCTURE WITH 36, AND KRYPTON IS ELEMENT NUMBER 36. SO THE STRONTIUM THEN AS IT BECOMES A POSITIVE TWO WILL HAVE A NOBLE GAS-LIKE STRUCTURE. SO WE CAN PUT DOWN STRONTIUM 2+, LOST TWO NEGATIVE CHARGES, AND THE SULFUR, S 2-, AND AGAIN THE ONLY WAY STRONTIUM AND SULFUR CAN COMBINE IS 1 TO 1 BECAUSE OF THEIR VALENCE ELECTRONS. YES, QUESTION? (STUDENT NOT AUDIBLE) WELL, WHEN WE DO IT AS FAR AS THE IONS WE WOULDN T PUT ANYTHING. THE QUESTION WAS DO I PUT DOTS HERE OR X S OR WHATEVER AND IT DOESN T MAKE ANY DIFFERENCE. WE RE JUST USING WHATEVER MANNER WE WANT TO TO IDENTIFY. IF WE WANTED TO SHOW THIS WE COULD WRITE SR AND THEN WE COULD WRITE S WHICH NOW WOULD HAVE THE DOTS AND I CAN PUT AN X FORT HE ONES THAT IT GAINED, DOTS BEING THE ONES IT HAD ITSELF AND THEN X THE ONE IT S GAINED, BUT AGAIN THIS IS WRITTEN THIS WAY, AND AGAIN THE CHEMICAL FORMULA IS SRS, IT S THE ONLY CHEMICAL

5 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 5 FORMULA WE CAN HAVE FOR STRONTIUM SULFIDE. NOW LET S LOOK AT SOMETHING THAT DOESN T COMBINE 1 TO 1. LET S TAKE ANOTHER METAL, THIS TIM E WE RE GOING TO TAKE A METAL FROM THIS THIRD COLUMN SO WE RE IN THE P BLOCK, THIS IS A METAL, GALLIUM. GALLIUM HAS THREE VALENCE ELECTRONS AND LET S REACT IT WITH SOME IODINE. IODINE HAS SEVEN VALENCE ELECTRONS. WELL, IF WE LOOKED AT THIS WE COULD SAY, ALRIGHT, I CAN SEE THAT GALLIUM COULD GIVE ONE OF ITS ELECTRONS TO IODINE AND IF WE DID THAT WE WOULD NOW PRODUCE THEN A GA +, BUT THE GA + STILL HAS TWO ELECTRONS AND WE WOULD PRODUCE AN I - ION WHICH NOW HAS8. SO THAT I - IS ALREADY LIKE THE NOBLE GAS. IT S NOT GOING TO TAKE ON ANY ADDITIONAL ELECTRONS. SO IF THE GALLIUM WHICH STILL HAS TWO ELECTRONS, YOU NOTICE THE GALLIUM HASN T BECOME LIKE A NOBLE GAS YET, IF THE GALLIUM NOW STILL HAS TWO ELECTRONS THEN IT MAY BE WANTING TO GET RID OF THOSE. WELL WE CAN GO DOWN HERE AND WE CAN SHOW THAT THE GALLIUM PLUS ION PRODUCED IN THE FIRST STEP NOW COULD GIVE AN ELECTRON TO A SECOND IODINE ATOM, PRODUCING NOW A GA 2+, STILL HAS ONE ELECTRON LEFT, DOESN T MAKE ANY DIFFERENCE WHERE WE PUT IT, PLUS ANOTHER IODIDE ION, AND THAT STILL HASN T ACHIEVED NOBLE GAS- LIKE STRUCTURE. SO FINALLY THE GALLIUM 2+ GIVES UP ITS THIRD ELECTRON AND WE VE BORN THEN NOW A GA 3+ AND ANOTHER I - ION. SO WHEN WE GET ALL DONE, THIS IS WHAT WE HAVE AS THE FINAL AND THIS IS WHAT WE HAVE AS THE FINAL AND SO THEREFORE WE COULD SEE THAT WHAT WE RE GOING TO END UP WITH IS GAI 3. THE WAY THAT GALLIUM AND IODINE COMBINE IS ONE GALLIUM REACTS WITH THREE IODINES. THAT S THE ONLY CHEMICAL FORMULA THAT WE RE GOING TO HAVE FOR THAT COMPOUND. SO IT DOESN T ALWAYS HAVE TO BE A 1 TO 1 GIVING PROCESS. IN THIS CASE WE HAVE THEN A 3 TO 1 GIVE AND TAKE PROCESS BUT AGAIN WE CAN SEE WHY THE CHEMICAL FORMULA GALLIUM IODIDE IS GAI 3, NOT GAI 2, NOT GA 2 I 3. GAI 3 IS THE ONLY WAY THAT GALLIUM AND IODINE CAN GET TOGETHER. NOW GALLIUM IS NOT WAY OVER THERE WHERE I MENTIONED BUT GALLIUM IS A METAL. REMEMBER ANYTHING BELOW THAT JAGGED LINE IS A METAL AND SO AS A METAL IT STILL HAS A TENDENCY TO WANT TO GIVE UP ELECTRONS. THE TRANSITION METALS ARE A LITTLE LESS SO. THE METALS IN THE D BLOCK AS WE MENTIONED ARE A LITTLE LESS ABLE TO GIVE UP

6 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 6 ELECTRONS AND SOMETIMES WE SEE THAT THEY DO, SOMETIMES WE FIND THAT THEY ACTUALLY DO A SHARING PROCESS. SO WE LL TALK ABOUT THAT A LITTLE BIT. ALRIGHT, ANY QUESTIONS ON THIS IDEA OF THE GIVE AND TAKE? OKAY, NOW LET S TURN TO THE SHARING PROCESS, AND THE SHARING PROCESS IS REFERRED TO AS COVALENT. OF COURSE WE KNOW THAT PREFIX CO, LIKE TO COLLABORATE. CO-OWNERS, WHATEVER THE CASE IS, TALKS ABOUT A SHARING OF SOMETHING. SO COVALENT MEANS A SHARING OF VALENCE ELECTRONS. SO IF TWO THINGS COME TOGETHER FOR INSTANCE AND THEY CANT BECOME INVOLVED IN A GIVE AND TAKE PROCESS THEN THEY MIGHT ACHIEVE A NOBLE GAS-LIKE STRUCTURE BY A SHARING PROCESS. ALRIGHT, NOW IF YOU RECALL WE TALKED ABOUT THE FACT THAT MOST OF TH ELEMENTS ARE MONOATOMIC THEY EXIST AS SINGLE ATOMS, BUT THERE ARE SOME ELEMENTS AT NORMAL CONDITIONS, ROOM CONDITIONS, THAT EXIST AS MOLECULES. REMEMBER HYDROGEN EXISTS AS H2. NITROGEN, OXYGEN BOTH EXIST AS DIATOMIC MOLECULES, N2 AND O2. THE HALOGENS, FLUORINE, CHLORINE, BROMINE, IODINE AND ASTATINE ARE ALL DIATOMIC MOLECULES IN NATURE. WELL THERE MUST BE SOME REASON THAT T HEY EXIST AS THOSE MOLECULES. THERE MUST BE SOMETHING THAT ENERGY STABILIZES THEM TO EXIST AS THAT FORM RATHER THAN BEING INDIVIDUAL ATOMS. WELL LET S LOOK AT HYDROGEN HERE FOR JUST A SECOND. HYDROGEN, ATOMIC NUMBER 1 HAS ONE ELECTRON AND WE LL HAVE ANOTHER HYDROGEN ATOM AND IT HAS ONE ELECTRON. NOW IF THESE TWO HYDROGENS WERE TO COME TOGETHER AND THEY MIGHT THEN SAY WELL, LISTEN, I M WILLING TO SHARE MY ELECTRON WITH YOU IF YOU RE WILLING TO SHARE YOUR ELECTRON WITH ME, AND IN THE PROCESS NOW YOU SEE THIS HYDROGEN OVER HERE WOULD SEE TWO ELECTRONS AROUND ITS NUCLEUS AND THIS HYDROGEN OVER HERE WOULD SEE TWO ELECTRONS AROUND ITS NUCLEUS. NOW WHAT ELEMENT HAS TWO ELECTRONS? HELIUM. SO BY SHARING THIS ELECTRON PAIR, BY EACH ONE DONATING ONE ELECTRON TO FORM THEN A SHARING PROCESS THEN WE HAVE FORMED A NOBLE GAS-LIKE ELECTRON STRUCTURE ONCE AGAIN. THE HYDROGEN MOLECULE, THE ATOMS IN THE HYDROGEN MOLECULE NOW HAVE THE SAME ELECTRON FEELING AS A HELIUM DOES. THEY HAVE A FILLED 1S ORBITAL. NOW WE CAN SHOW THIS IN SORT OF A PICTURE FORM AS WELL HERE, PUTTING TOGETHER HERE NOW WE RE

7 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 7 SAYING ALRIGHT WE HAD A HYDROGEN. IT HAD ONE ELECTRON IN THE 1S. REMEMBER, THE 1S ORBITAL IS JUST A SPHERICAL SPACE AND THE ELECTRON IS IN THERE AND IT CAN BE ANYWHERE. MATTER OF FACT, IT S THE PROBABILITY PLOT OF WHERE IT IS. SO THAT ELECTRON COULD BE ANYWHERE. WHAT WE RE GOING TO SHOW IS THAT THAT ELECTRON NOW TENDS TO MOVE OVER IN THIS AREA BECAUSE IT SEES THE OTHER POSITIVE NUCLEUS AND OF COURSE THE OTHER ELECTRON THAT WAS INVOLVED FROM THE OTHER HYDROGEN ALSO IS ATTRACTED AND SO WE END UP WITH THEN THE PAIR OF ELECTRONS NOW LOCATED BETWEEN THE TWO HYDROGENS. SO WE HAVE A PAIR OF SHARED ELECTRONS INVOLVED HERE THAT ACCOUNTS FOR THEN WHY THESE ARE HELD TOGETHER. THEY RE NOT HELD TOGETHER BECAUSE OF ELECTROSTATIC ATTRACTION. THEY RE HELD TOGETHER BECAUSE OF SIMULTANEOUS ATTRACTION FOR A PAIR OF SHARED ELECTRONS. THAT S A COVALENT BOND. THEY USUALLY SHOW THIS WHEN WE RE WRITING STRUCTURAL FORMULA AS A DASH (-). A DASH IN A FORMULA INDICATES A PAIR OF SHARED ELECTRONS, THAT S WHAT THAT DASH REPRESENTS. NOW I SAID ALSO THAT FLUORINE AND CHLORINE AND BROMINE AS THE HALOGEN FAMILY ALL EXIST AS DIATOMIC MOLECULES ALSO. BEFORE WE LOOK AT THE STRUCTURE WE LL JUST LOOK AT THE ELEMENTS HERE. WE HAVE CHLORINE, DIATOMIC, YES AT ROOM TEMPERATURE. WE HAVE BROMINE, A REDDISH-BROWN LIQUID. WE SEE A FAIR AMOUNT OF GAS ABOVE IT, BUT IT S PRIMARY STATE AT ROOM TEMPERATURE IS A LIQUID. AS A MATTER OF FACT, REMEMBER BROMINE IS THE ONLY NON-METAL THAT IS A LIQUID AT ROOM TEMPERATURE, AND MERCURY IS THE ONLY METAL THAT IS A LIQUID AT ROOM TEMPERATURE. AND FINALLY WE HAVE IODINE. IT S A LITTLE HARD TO SEE IN THIS PARTICULAR PICTURE, BUT ACTUALLY THE IODINE NOW IS SOME SOLID CRYSTALS LOCATED DOWN HERE IN THE BOTTOM OF THE FLASK. IODINE CRYSTALS ALMOST LOOK LIKE METALS, SHINY LITTLE GRAY FLAKES. BUT THERE IS ENOUGH MOLECULES OF IODINE THAT ESCAPE FROM THE SOLID THAT WE SEE SOME OF THE IODINE IN THE GASEOUS PHASE ABOVE IT HERE, AND IODINE IN THE GASEOUS PHASE HAS A PURPLE COLOR TO IT. BUT THE THREE THEN DIFFERENT HALOGENS, CHLORINE A GAS, BROMINE A LIQUID, AND IODINE A SOLID, AT ROOM TEMPERATURE, ALL ARE DIATOMIC MOLECULES ALONG WITH FLUORINE. WE DON T SHOW FLUORINE HERE, IT S JUST A COLORLESS

8 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 8 GAS, AND SO IT WOULD LOOK LIKE AN EMPTY FLASK ANYWAY, BUT IT IS IN THE GASEOUS STATE. WELL LET S SEE IF WE CAN UNDERSTAND THEN WHAT IT IS THAT ALLOWS FLUORINE NOW, WHICH WOULD ALSO REPRESENT CHLORINE, BROMINE, AND IODINE, BECAUSE THEY ALL HAVE EXACTLY THE SAME ELECTRON STRUCTURE, HOW DO THEY GET TOGETHER TO FORM DIATOMIC MOLECULES? WELL I VE DRAWN HERE THE PICTURE OF EACH OF THE FLUORINE ATOMS. I JUST PUT THEM IN SLIGHTLY DIFFERENT COLOR THEN SO WE D SEE THEN WHAT IS OCCURRING. EACH FLUORINE, CHLORINE, BROMINE, IODINE, EACH HALOGEN HAS SEVEN VALENCE ELECTRONS. SO WE SEE HERE NOW THAT WE HAVE FLUORINE WITH PAIR PAIR PAIR AND A SINGLE FOR ITS SEVEN, THE OTHER FLUORINE WITH ITS SEVEN. EACH ONE WOULD LIKE TO HAVE EIGHT, SO AGAIN WE RUN INTO THE SITUATION WHERE WE CAN SAY THIS FLUORINE SAYS I LL SHARE THIS ELECTRON WITH YOU, THIS FLUORINE SAYS ALRIGHT I LL SHARE THIS ELECTRON WITH YOU. WE NOW HAVE A PAIR OF SHARED ELECTRONS IN THERE. IF WE THEN PUT A CIRCLE AROUND HERE WE SEE THAT WE HAVE IN FACT EIGHT ELECTRONS NOW AVAILABLE TO THE FLUORINE NUCLEUS AND OVER HERE THIS ONE ALSO HAS EIGHT ELECTRONS AROUND IT. SO EACH HAS A NOBLE GAS-LIKE STRUCTURE. SO WE RE SHARING A PAIR OF ELECTRONS. TO SHOW THE MOLECULE THEN WE WRITE IT IN THIS FASHION WITH A DASH IN BETWEEN. SOMETIMES IN STRUCTURAL FORMULAS WE MERELY WRITE THE SYMBOL. SO WE COULD WRITE IT LIKE THIS. CHEMICALLY IN AN EQUATION WE WOULD WRITE IT LIKE THAT. IT ALL MEANS THE SAME THING. BUT WE WILL BE INTERESTED IN THESE OTHER ELECTRONS AS WELL AS WE GET IN TO TALKING ABOUT MOLECULAR GEOMETRY AND THAT IS THAT THESE ELECTRONS HERE ARE REFERRED TO AS NON-BONDING ELECTRONS. QUITE OBVIOUSLY THEY RE NOT INVOLVED IN THE SHARING PROCESS SO THEY RE CALLED NON- BONDING ELECTRONS. AND NON-BONDING ELECTRONS AS I SAY WILL BE IMPORTANT TO US WHEN WE CONSIDER MOLECULAR GEOMETRY. NOW, FROM A PHYSICAL STANDPOINT LET S SEE WHAT THIS LOOKS LIKE. NOW REMEMBER WE HAVE FOUR VALENCE ORBITALS, S AND THREE P S, AND REMEMBER THE P S WERE ALWAYS SLIGHTLY HIGHER IN ENERGY THAN THE S. SO PUTTING ELECTRONS IN NOW, WE RE GOING TO PUT A PAIR INTO THE S AND THEN A PAIR INTO THE P AND A PAIR INTO THE P AND ONE IN THE OTHER P. SO ONE OF THE P ORBITALS HAS ONLY

9 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 9 A SINGLE ELECTRON IN IT. SO IF WE LOOK AT THIS THEN WE RE SAYING HERE IS NOW THE FLUORINE ATOM. 2P ORBITAL, REMEMBER AN ORBITAL, P ORBITAL, IS A FIGURE EIGHT SHAPE STRUCTURE. THAT DOUBLE LOBE, THAT DOUBLE LOBE RIGHT THERE CONTAINS JUST ONE ELECTRON. IT COULD BE ON EITHER SIDE OF THE NUCLEUS BUT AS TWO FLUORINE ATOMS APPROACH EACH OTHER THEN THE ELECTRON FROM THIS ONE MIGHT BE ON THAT SIDE AND THE ELECTRON IN THIS ONE MIGHT BE ON THAT SIDE IT HAS EQUAL PROBABILITY WHEN THE ATOMS ARE ALL BY THEMSELVES OF BEING ON EITHER SIDE. BUT NOW AS THESE POSITIVE NUCLEI COME TOGETHER THESE ELECTRONS TENDS TO MOVE IN BETWEEN SO THAT THIS ONE NOW BECOMES ATTRACTED TO THAT NUCLEUS AND THIS ONE BECOMES ATTRACTED TO THAT NUCLEUS. WHEN WE GET ALL DONE NOW WE HAVE A PAIR OF ELECTRONS SITTING HERE IN BETWEEN THE TWO FLUORINES AND THAT S WHAT THEN ACCOUNTS FOR THE CHEMICAL BOND WE SHOW AS THE DASH. THAT S THAT PAIR OF SHARED ELECTRONS BETWEEN THE TWO. SO AS I SAY, BECAUSE THEY RE IN THE SAME FAMILY OF COURSE THIS EXPLAINS THE BEHAVIOR OF ALL OF THOSE, FLUORINE, CHLORINE, BROMINE, IODINE AND ASTATINE. BUT THERE ARE THE TWO OTHER DIATOMIC MOLECULES OXYGEN AND NITROGEN. LET S LOOK AT OXYGEN FIRST OF ALL. NOW OXYGEN IS IN THE SIXTH COLUMN, TELLING US IT HAS SIX VALENCE ELECTRONS. SO OF WE WERE TO BRING TWO OXYGENS TOGETHER AND AGAIN I VE COLORED THESE SO THAT WE CAN KIND OF FOLLOW WHAT S GOING ON. THIS OXYGEN HAS SIX VALENCE ELECTRONS, THIS HAS SIX VALENCE ELECTRONS. TO BE LIKE A NOBLE GAS WE HAVE TO EACH HAVE AN OCTET, OR EIGHT. WELL AGAIN, THIS OXYGEN UP HERE SAYS I LL SHARE THIS ELECTRON WITH YOU AND THIS ONE WITH YOU, PROVIDED THAT YOU WILL SHARE THIS ELECTRON WITH ME AND THIS ONE WITH ME, AND IF WE DO THAT THEN OF COURSE WE RE GONNA END UP WITH THE TWO OXYGENS NOW WITH ACTUALLY FOUR ELECTRONS BEING SHARED BETWEEN THE TWO AND THEN OF COURSE EACH ONE WOULD STILL HAVE ITS OWN NON-BONDING ELECTRONS THAT WEREN T SHARED. THESE TWO PAIRED HERE AND THESE TWO PAIRED HERE NOW ARE NOT BEING SHARED, THOSE ARE THE NON-BONDING ELECTRONS. NOW A CHEMICAL BOND REPRESENTS A PAIR OF SHARED ELECTRONS. IN THIS CASE WE HAVE TWO PAIRS OF SHARED ELECTRONS AND SO WE SHOW THIS THEN BY USING A DOUBLE DASH (--), WHICH IS CALLED A

10 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 10 DOUBLE BOND, WHICH IMPLIES THAT TWO PAIRS OF ELECTRONS, EACH DASH REPRESENTS A PAIR OF SHARED ELECTRONS. AND SO IF WE LOOK AT THIS OXYGEN HERE NOW YOU SEE IT HAS AROUND IT TWO, FOUR, SIX, EIGHT ELECTRONS. IF WE LOOK AT THIS OXYGEN HERE IT HAS TWO, FOUR, SIX, EIGHT ELECTRONS. BOTH SEE EIGHT ELECTRONS AROUND THE NUCLEUS AND IT S BECOME LIKE A NOBLE GAS. FINALLY NITROGEN, AND WE NOTICED NITROGEN ON THE PERIODIC TABLE IS ON THE FIFTH COLUMN MEANING THAT IT HAS FIVE VALENCE ELECTRONS. OBVIOUSLY TO GET AN OCTET IT HAS TO GAIN THREE. WELL IF WE LOOK AT THE ELECTRON ARRANGEMENT OF THE NITROGEN, AGAIN WE CAN SHOW THAT IT WOULD HAVE TO HAVE A PAIR AND THREE SINGLES IN ITS FIVE ELECTRON STRUCTURE AND THE OTHER NITROGEN WOULD HAVE A PAIR AND THREE SINGLES. SO THIS TIME THE NITROGEN S THEN ARE GOING TO SAY ALRIGHT, I LL DONATE THIS ONE, YOU DONATE ONE. I LL DONATE THIS ONE, YOU DONATE ONE, I LL DONATE ANOTHER ONE, YOU DONATE ANOTHER ONE, AND SO WE END UP THEN WITH NITROGEN NOW WITH ONE, TWO, THREE PAIRS OF ELECTRONS THAT THE TWO NITROGENS ARE SHARING. WE THEN OF COURSE EACH NITROGEN STILL HAS THIS PAIR OF ELECTRONS NON- BONDING PAIR OF ELECTRONS THAT WEREN T SHARED, BUT IF WE LOOK AT THIS NITROGEN HERE IT NOW SEES EIGHT ELECTRONS. IF WE LOOK AT THIS NITROGEN HERE IT IS NOW SEEING EIGHT ELECTRONS. THIS TIME WE HAVE SHARED THREE PAIRS OF ELECTRONS AND WE THEN SHOW THIS IN THE FORMULA BY THREE DASHES, CALLED A TRIPLE-BOND (---), THREE PAIRS OF ELECTRONS ARE BEING SHARED. NOW, THERE ARE ONLY A FEW ELEMENTS THAT REALLY CAN SHARE MORE THAN ONE PAIR OF ELECTRONS. CARBON CAN SHARE A SINGLE PAIR, TWO PAIR, OR THREE PAIR. NITROGEN CAN SHARE SINGLE, TWO PAIR OR THREE PAIR. THESE ARE THE ONLY TWO ELEMENTS UNDER NORMAL CHEMICAL REACTION CONDITIONS THAT CAN SHARE THREE ELECTRON PAIRS. ONLY CARBON AND NITROGEN CAN FORM A TRIPLE BOND OKAY. NOW, BOTH CARBON AND NITROGEN CAN FORM DOUBLE BONDS BUT THERE ARE A FEW OTHER THINGS THAT CAN FORM DOUBLE BONDS AS WELL. OXYGEN, SULFUR, PHOSPHORUS, SILICON, THAT S FOUR OTHER ELEMENTS THAT CAN FORM DOUBLE BONDS, SHARE TWO PAIR OF ELECTRONS. THE REST OF THE ELEMENTS, WHEN WE RE DOING COVALENT STRUCTURES, ARE ONLY GOING TO SHARE A SINGLE PAIR OF ELECTRONS. NOW, IT MAY SHARE A SINGLE PAIR OF

11 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 11 ELECTRONS WITH THREE DIFFERENT THINGS, BUT IT WILL ONLY SHARE ONE PAIR BETWEEN EACH INDIVIDUAL ATOM IN THE MOLECULE. SO THERE ARE ONLY A FEW THAT WE HAVE TO WORRY ABOUT THAT ARE INVOLVED THEN THESE SIC RIGHT HERE THAT ARE INVOLVED IN WHAT WE CALL MULTIPLE-BONDS, WHICH MEANS OF COURSE EXTRA PAIRS OF SHARED ELECTRONS. NOW ONE OF THE AREAS OF CHEMISTRY THAT WE HAVE BEEN TALKING ABOUT OF COURSE IS THE ORGANIC CHEMISTRY AND IF WE LOOK UP THERE I JUST MENTION THAT CARBON HAS THE ABILITY TO FORM SINGLE, DOUBLE, AND TRIPLE BONDS, AND SO WE FIND THAT FREQUENTLY IN ORGANIC COMPOUNDS, CARBON BASED CHEMISTRY THAT WE DO HAVE THIS MULTIPLE BONDING PROCESS. FOR INSTANCE, ONE THAT WE VE ALREADY LOOKED AT, WE LOOKED AT THE CARBOXYLIC ACIDS AND WE DREW THIS AS THE GENERAL STRUCTURE OF THE CARBOXYLIC ACID. WE DIDN T HAVE THE LITTLE X S ON THERE BEFORE, BUT THE STRUCTURE SHOWED US THAT THE CARBON HAD TWO BONDS TO THE OXYGEN. THAT MEANS THAT THE CARBON AND THE OXYGEN ARE SHARING TWO PAIRS OF ELECTRONS BETWEEN THE TWO. NOW ONE OTHER THING THAT WE HAVE SAID BEFORE, CARBON CAN ONLY FORM FOUR BONDS. THAT IS BECAUSE OF COURSE WE ONLY HAVE FOUR VALENCE ORBITALS. WHEN WE FILL THOSE WE CAN T THEN SHARE ANYTHING MORE. SO CARBON FORMS ONLY FOUR BONDS. IN THIS CASE WE SHOW THAT A SHARING A PAIR OF ELECTRONS OF WHATEVER THIS GROUP IS OUT HERE, A PAIR OF ELECTRONS TO THIS OXYGEN AND TWO PAIRS OF ELECTRONS WITH THIS OXYGEN. SO WE SEE THE CARBON HAS IN FACT FOUR COVALENT BONDS. AND THEN WE SEE THIS OXYGEN OF COURSE IS SHARING ONE PAIR WITH THE CARBON, ONE PAIR WITH THE HYDROGEN, SO AS FAR AS THE OXYGEN IS CONCERNED IT HAS EIGHT ELECTRONS, AND AS FAR AS THIS CARBON IS CONCERNED IT HAS EIGHT ELECTRONS TWO, FOUR, SIX, EIGHT. THIS OXYGEN HAS EIGHT ELECTRONS TWO, FOUR, AND THEN FOUR NON-BONDING ELECTRONS. THE HYDROGEN HAS TWO ELECTRONS, AND OF COURSE THAT S ALL HYDROGEN WANTS BECAUSE THAT MAKES IT LIKE HELIUM. SO EVERYTHING IN THAT CARBOXYLIC ACID HAS SATISFIED THEN THE OCTET THROUGH EITHER A SINGLE BOND, A SINGLE SHARING PROCESS OR A DOUBLE SHARING PROCESS. NOW THERE IS A GROUP OF HYDROCARBONS, WE VE TALKED ABOUT HYDROCARBONS BEFORE. HYDROCARBONS ARE THOSE ORGANIC COMPOUNDS CONTAINING

12 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 12 ONLY CARBON AND HYDROGEN. THE FIRST ONES WE TALKED ABOUT WE CALLED SATURATED HYDROCARBONS. NOW WE RE GOING TO LOOK AT THE GROUP THAT WE CALL UNSATURATED. UNSATURATED HYDROCARBONS MEANS THAT THEY HAVE AT LEAST ONE CARBON-CARBON DOUBLE OR TRIPLE BOND IN THE STRUCTURE. HYDROCARBONS THAT CONTAIN ONLY CARBON- CARBON SINGLE BONDS ARE CALLED SATURATED HYDROCARBONS. WE ALREADY LOOKED AT THOSE SEVERAL TIMES. LET S JUST TAKE THE FIRST GROUP OF THESE. WE VE ALREADY TALKED ABOUT THE TWO-CARBON SATURATED. THIS IS THE SATURATED ONE, THIS IS THE ONE THAT WE TALKED ABOUT BEFORE OKAY. THIS IS THE AS I SAY SATURATED AND WE CALLED IT ETHANE. THE ENDING ANE INDICATED ONLY CARBON-CARBON SINGLE BONDS. IF I PUT A DOUBLE BOND BETWEEN THE CARBONS IT S STILL LIKE AN ETHANE BUT WE CHANGE THE ENDING AND THE NAME TO ENE, AND THAT ENDING ENE, WHEN I SEE IT IN THE NAME OF AN ORGANIC COMPOUND IMPLIES A CARBON-CARBON DOUBLE BOND IN THE STRUCTURE. AND FINALLY, WHEN WE PUT THE TWO CARBONS TOGETHER BUT WE SHARE THREE PAIRS OF ELECTRONS AND IF WE LOOKED AT THESE AND EVERY CARBON STILL IS ACHIEVING AN OCTET WE CALL THIS A (NOT AUDIBLE) STRUCTURE. THE YNE, WHEN I SEE THAT IN AN ORGANIC COMPOUND NAME IT INDICATES THE PRESENCE OF A CARBON-CARBON TRIPLE BOND, THREE PAIRS OF SHARED ELECTRONS. NOW, THIS CONTINUES ON. JUST LIKE WE DID, WE HAD ETHANE, PROPANE, BUTANE, PENTANE, HEXANE AND SO ON. WE HAVE THE SAME TYPE OF THING THAT WOULD OCCUR AS WE WENT ON TO THE OTHERS. IF WE GO TO THE THREE CARBON SATURATED IT S PROPANE. THE THREE CARBON WITH THE DOUBLE BOND IN IT IS PROPENE. THE THREE CARBON WITH THE TRIPLE BOND IN IT PROPYNE, AND SO WE CAN CONTINUE ON USING THAT NOMENCLATURE SYSTEM. BUT IF YOU RECALL IN THE SATURATED HYDROCARBONS WE DID SEE THAT WE CAN HAVE THE SAME CHEMICAL FORMULA BUT PUT IT TOGETHER IN MORE THAN ONE WAY, AND THESE WE CALLED ISOMERS, AND SO YES WE HAVE ISOMERS WHEN WE RE INVOLVING UNSATURATED HYDROCARBONS. AS A MATTER OF FACT, WE CAN HAVE MORE ISOMERS WHEN WE HAVE UNSATURATED HYDROCARBON BECAUSE NOT ONLY CAN WE HATCH LITTLE SIDE GROUPS LIKE WE DID, PUT IN A CH3 GROUP, METHYL GROUP OR A C2H5 GROUP, METHYL GROUP, HANG IN DIFFERENT PLACES. NOT ONLY CAN WE DO THAT, BUT W CAN MOVE

13 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 13 THE DOUBLE BOND OR TRIPLE BOND AROUND AND THAT MAKE A NEW COMPOUND. NOW, DON T BOTHER WRITING ANY OF THESE DOWN. YOU RE NOT RESPONSIBLE FOR THIS, BUT I JUST WANTED TO SHOW YOU HERE QUICKLY WHAT WE MEAN BY THE ISOMERS INVOLVING THE UNSATURATED. THESE ARE ALL FIVE CARBON STRUCTURES. FIVE IN A ROW WOULD BE PENTANE, BUT IF WE HAVE THE DOUBLE BOND IT S PENTENE, BUT THERE ARE TWO WAYS WE AN PUT THE DOUBLE BOND. WE CAN PUT IT STARTING ON THE FIRST CARBON OR WE CAN START IT ON THE SECOND CARBON AND THOSE ARE TWO UNIQUE MOLECULES. THE WAY WE IDENTIFY THE DIFFERENCE NOTICE THE BASE NAME IS STILL PENT, MEANING FIVE, BOTH ARE ENE, MEANING A DOUBLE BOND, BUT WE PUT THE NUMBER ONE OR TWO IN FROM \NT WITH A DASH TO INDICATE WHERE THAT DOUBLE BOND IS STARTING. WELL NOT ONLY THEN, DOWN HERE, THE NEXT ISOMER, WE RE GOING TO PUT FOUR IN A ROW. SO WE RE GOING TO MAKE IT BUTENE, AND THEN WE RE GOING TO HANG A GROUP UNDERNEATH, THE METHYL GROUP. SO WE CALL IT 2-METHYL, THE METHYL GROUP IS ON THE SECOND CARBON, AND THE BASE COMPOUND IS 1-BUTENE. IT S A FOUR CARBON WITH A DOUBLE BOND STARTING ON NUMBER ONE. OKAY, AND THEN THIS ONE, THE METHYL GROUP IS STILL ON THE NUMBER TWO, BUT NOW THE DOUBLE BOND HAS BEEN MOVED TO NUMBER TWO SO WE HAVE 2-METHYL 2-BUTENE. OKAY, AGAIN, DON T WORRY ABOUT THE NAMING OR DRAWING OF THESE, BUT WE JUST WANT TO SHOW. AND HERE THEN OF COURSE WE COULD HAVE THE DOUBLE BOND HERE AND MOVE THE METHYL GROUP AND WE HAVE ANOTHER NEW MOLECULE. SO YOU SEE THAT WE CAN REALLY GET A LOT OF ISOMERS ONCE WE BEGIN LOOKING AT UNSATURATED HYDROCARBONS. I DREW THIS ONE HERE JUST TO SHOW THAT WE COULD DRAW THIS AS A PROPENE WITH TWO METHYL GROUPS BUT I PUT AN X THROUGH IT AND WHY DID I PUT AN X THROUGH IT? (STUDENT RESPONSE NOT AUDIBLE) CARBON HAS FIVE BONDS. THE CENTER CARBON HERE WE HAVE ONE, TWO, THREE, FOUR, FIVE ELECTRON PAIRS BEING SHARED WHICH IS TEN WHICH IS NOT AN OCTET WHICH DOESN T MAKE SENSE THAT IT WOULD BE ENERGY STABLE, AND SO THAT ISOMER, EVER THOUGH WE COULD DRAW IT DOESN T FIT THAT CARBON FORM ONLY FOUR BONDS TOTAL. ALRIGHT, NOW WHAT IF WE HAVE MORE THAN ONE DOUBLE BOND IN A MOLECULE? WELL WE CALL THOSE THEN POLYUNSATURATED AND CERTAINLY THAT S A TERM

14 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 14 THAT YOU VE HEARD. IF YOU VE HEARD ANY COMMERCIALS ON MARGARINE AND BUTTERS AND THINGS LIKE THIS AND COOKING OILS, ONE OF THE KEY WORDS IN THE ADVERTISEMENT IS POLYUNSATURATED. IF THEY CAN SAY THAT, IF THEY CAN SAY THAT THE OIL IS POLYUNSATURATED THAT MEANS THAT IT, WELL IT DOESN T REALLY MEAN IT, THAT IS TO IMPLY THAT IT IS HEALTHY FOR US. POLYUNSATURATED OILS CONTAIN THEN MOLECULES THAT HAVE DOUBLE BONDS IN THEM, WHICH SUPPOSEDLY IS EASIER FOR US TO DIGEST AND LESS LIKELY TO LEAD TO A CHOLESTEROL BUILDUP. AND SO WHEN WE RE LOOKING AT DIFFERENT TYPES OF COOKING MATERIALS. ANIMAL OILS USUALLY ARE SATURATED OILS, MEANING THEY HAVE ALL CARBON-CARBON SINGLE BONDS. OILS FROM VARIOUS GRAINS LIKE SAFFLOWER, SOYBEAN, CORN, THOSE ARE POLYUNSATURATED OILS, THEREFORE IF WE COOK WITH THOSE AND WE EAT SOME OFT HEM FROM THE COOKING PROCESS THEY SHOULD BE MORE EASILY DIGESTED AND LESS LIKELY TO LEAD TO CHOLESTEROL. ALRIGHT, THERE S STILL A LOT OF DEBATE ON THE TOTAL EFFECT OF BOTH, BUT THIS WOULD REPRESENT NOW A POLYUNSATURATED MOLECULE. NOTICE THAT I HAVE A TRIPLE BOND AND A DOUBLE, TWO DOUBLE BONDS IN THERE. SO IT HAS TWO OR MORE DOUBLE OR TRIPLE BONDS AND IS CALLED POLYUNSATURATED. NOW, ONE OTHER THING THAT WE TALKED ABOUT IN THE SATURATED OR SINGLE BONDS WERE THE CYCLIC COMPOUNDS, AND WE CAN HAVE CYCLIC COMPOUNDS THAT INVOLVE MULTIPLE BONDS AS WELL. THAT WAS CYCLOBUTANE, FOUR CARBONS HOOKED TOGETHER IN A LOOP. IF WE HOOK FOUR CARBONS TOGETHER IN A LOOP AND BUT ONE DOUBLE BOND IN IT IT BECOMES CYCLOBUTENE, AND THE ENE IS INCLUDED THERE AS TO THE NAME AND THE DOUBLE BOND. WE COULD ALSO HAVE POLYUNSATURATED CYCLO HYDROCARBONS. IF WE LOOK AT THIS ONE HERE, THIS IS SIX CARBONS WITH ALTERNATING SINGLE-DOUBLE-SINGLE-DOUBLE-SINGLE-DOUBLE BONDS SIX CARBONS. OKAY, SO THE BASE NAME WOULD BE CYCLOHEXENE, ENE TO SHOW DOUBLE BONDS, BUT THERE ARE THREE OF THEM IN THERE SO IT WOULD HAVE TO BE CYCLOHEXATRIENE TO SHOW THREE DOUBLE BONDS, AND AS A MATTER OF FACT, WE D HAVE TO TELL WHERE THEY WERE. IN OTHER WORDS THAT THEY WEREN T ADJACENT TO EACH OTHER. SO THE ACTUAL NAMING OF THIS IS 1,3,5 CYCLOHEXATRIENE. DON T WORRY ABOUT THAT. ALRIGHT, THIS IS USUALLY DRAWN IN THIS

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

16 CHM 105 & 106 MO1 UNIT THREE, LECTURE TEN 16 FACT THAT IF WE WERE TO SHOW THIS MOLECULE, AND THESE PAIR OF ELECTRONS IS ACTUALLY SPENDING MORE TIME OVER HERE BY THE CHLORINE, IT MEANS THAT THIS END OF THE MOLECULE IS GOING OT BE SLIGHTLY NEGATIVE AND THIS END OF THE MOLECULE IS GOING TO BE SLIGHTLY POSITIVE, OR THIS END OF THE BOND, I SHOULD SAY, WILL BE SLIGHTLY POSITIVE. SO WE HAVE A SLIGHTLY POSITIVE AND A SLIGHTLY NEGATIVE END, AND SO WE RE TALKING ABOUT POLAR COVALENT. BUT WHEN I PUT SODIUM AND CHLORINE TOGETHER, THAT PAIR OF ELECTRONS THAT WE HAVE BETWEEN, SODIUM ONLY HAS AN ATTRACTION OF ABOUT.9, CHLORINE 3.0. IT S DEFINITELY UNEQUAL, BUT IT S SO UNEQUAL THAT WE ACTUALLY CONSIDER THAT THE ELECTRON SPENDS ALL OF ITS TIME WITH THE CHLORINE. AS A MATTER OF FACT, THE GUIDELINE THAT WE USE IS IF THE ELECTRONEGATIVITY DIFFERENCE CALL IT DELTA EL ( EL), IF THE DIFFERENCE IN THE ELECTRONEGATIVITY OF THE TWO ATOMS IS GREATER THAN 1.6 WE SAY THAT IT IS IONIC IN ITS BONDING. IN OUR NEXT LECTURE THEN WE LL TAKE A LOOK AT THE ELECTRONEGATIVITY TABLE AND PREDICT SOME POLAR/NON- POLAR BONDS AND GO ON AND TALK ABOUT MOLECULAR GEOMETRY AND POLAR MOLECULES.