- WELCOME TO THE ELECTRONEGATIVITY
AND MOLECULAR POLARITY TUTORIAL.
THIS WILL BE A CLOSER LOOK AT COVALENT COMPOUNDS.
THIS IS A VERY IMPORTANT TOPIC.
SO LET'S GET STARTED, RIGHT?
SO WHEN WE TALK ABOUT COVALENT COMPOUNDS,
WE TALK ABOUT ELECTRON SHARING.
HOWEVER, IF WE THINK ABOUT IT,
DO WE THINK THAT ELECTRONS ARE ALL GOING TO BE SHARED EQUALLY?
NO, RIGHT?
BUT IT DEPENDS ON WHO IS SHARING. OKAY.
AND I KNOW I TEND TO PERSONIFY THE ELEMENTS AND THE MORE
YOU GET TO KNOW THEM, YOU PROBABLY WILL TOO.
I MEAN, WHEN I THINK ABOUT ELECTRONS SHARING,
THERE ARE SOME PEOPLE IN MY LIFE I WOULD SHARE EVERYTHING WITH
AND THERE'S OTHER PEOPLE I'M NOT GOING TO BE SO GENEROUS WITH.
AND ELEMENTS ARE LIKE THAT TOO.
SO THIS IDEA OF ELECTRONEGATIVITY,
ON A REALLY SIMPLE LEVEL,
WE COULD THINK OF IT AS ELECTRON GREED.
SOME ELEMENTS ARE VERY GREEDY
AND THEY REALLY DON'T WANT TO SHARE THE ELECTRONS.
IT'S LIKE THEY BECOME COVALENT COMPOUNDS BEGRUDGINGLY.
IF YOU LOOK IN YOUR TEXTBOOK,
THEY WILL DEFINE ELECTRONEGATIVITY AS THE ABILITY
OF AN ELEMENT TO ATTRACT SHARED ELECTRONS TO ITSELF.
- JUST CENTER THE PAGE A LITTLE BIT.
- OH, JUST... - THAT IS PERFECT.
- OKAY. OKAY.
SO REMEMBER WHEN WE SEE SHARED ELECTRONS--
RIGHT, SO SHARED ELECTRONS,
THAT'S A COVALENT BOND.
ALL RIGHT.
SO HERE ARE THE TRENDS.
SO I HAVE SHOWN YOU THE NUMERICAL VALUES.
SOME STUDENTS REALLY LIKE THE NUMERICAL VALUES
BUT YOU REALLY DON'T HAVE TO KNOW THEM THAT WELL.
WE CAN JUST GO WITH THE TREND.
IF WE LOOK AT THE PERIODIC TABLE, RIGHT?
AND THESE TRENDS--
THESE TRENDS TEND TO FOCUS ON THE MAIN GROUP.
THEY'RE REPRESENTATIVE ELEMENTS,
THE ELEMENTS WHERE WE'RE FILLING THE S AND P SUBSHELLS.
AND IF WE LOOK AT ELECTRONEGATIVITY
WHICH IS WAY TOO LONG TO SAY,
SO WE WILL ABBREVIATE IT EN AND WE CAN SEE FROM THESE VALUES
THAT FLUORINE IN THIS CORNER IS THE MOST ELECTRONEGATIVE.
IT'S THE GREEDIEST.
AND THEN IF WE LOOK OVER HERE
IN THIS CORNER IN THE CESIUM-FRANCIUM AREA,
WE SEE THAT THESE ARE THE LEAST
ELECTRONEGATIVE AND THAT MAKES SENSE
WITH WHAT WE KNOW ABOUT THE ELEMENTS, RIGHT?
BECAUSE HERE'S OUR STAIR-STEP LINE AND SO
WE KNOW TO THE LEFT ARE THE METALS AND METALS
LIKE TO LOSE ELECTRONS.
AND THEN TO THE RIGHT OF THE STAIR-STEP,
WE HAVE THE NON-METALS AND NON-METALS
LIKE TO GAIN ELECTRONS.
SO THESE TRENDS
IN ELECTRONEGATIVITY MAKE PERFECT SENSE.
ELECTRONEGATIVITY INCREASES AS WE MOVE UP THE PERIODIC TABLE
AND ELECTRONEGATIVITY INCREASES AS WE MOVE FROM LEFT TO RIGHT.
SO WE DON'T NEED TO MEMORIZE
ALL OF THESE ELECTRONEGATIVITY VALUES.
WE SIMPLY NEED TO KNOW THE TREND.
AND THEN HOW THIS DIFFERENCES
IN ELECTRONEGATIVITY WORK IS THAT AT ONE EXTREME,
WE HAVE THE NON POLAR COMPOUNDS
AND THAT'S WHERE WE HAVE EQUAL SHARING OF ELECTRONS.
SO THERE'S NO DISTRIBUTION OF CHARGE.
AND THEN AS THE DIFFERENCE
IN ELECTRONEGATIVITY GETS LARGER AND LARGER AND LARGER,
WE ARBITRARILY SET A CUT-OFF
THAT IF THE DIFFERENCE GETS TOO LARGE,
WE CALL THEM IONIC COMPOUNDS
AND THAT'S WHERE WE HAVE A FULL POSITIVE CHARGE
AND A FULL NEGATIVE.
SO WHERE THINGS GET INTERESTING IS IN THIS GRAY REGION
RIGHT HERE WHERE WE HAVE THE UNEQUAL SHARING OF ELECTRONS
AND THIS CREATES POLES OF CHARGE
WHERE WE HAVE THE PARTIAL POSITIVE.
SO THIS SYMBOL HERE, THIS GREEK LOWERCASE DELTA,
THIS MEANS WE HAVE A PARTIAL POSITIVE CHARGE
AND WE HAVE A PARTIAL NEGATIVE CHARGE.
AND SO THIS IS WHERE WE WANT TO FOCUS OUR ATTENTION
IN THIS TUTORIAL WHERE WE HAVE A DIFFERENCE
IN ELECTRONEGATIVITY THAT IS IN THIS MIDDLE RANGE GREATER
THAN 0.4 IF WE USE THE NUMERICAL VALUES,
LESS THAN POINT--
THAN 1.8. OKAY.
SO WE'VE SEEN IT ON THE TABLE BUT LET'S LOOK--
IF WE'RE LOOKING AT COMPOUNDS, RIGHT?
IF WE'RE LOOKING AT COMPOUNDS,
NON POLAR COMPOUNDS MEANS THERE'S AN EQUAL SHARING
OF ELECTRONS.
SO THIS IS GOING TO BE ELEMENTS WHERE WE HAVE IDENTICAL ELEMENTS
LIKE TWO HYDROGEN ATOMS OR EVEN FLUORINE.
EVEN THOUGH FLUORINE IS THE MOST GREEDIEST
OF ALL OF THE ELEMENTS,
THE MOST ELECTRONEGATIVE.
IF WE HAVE TWO FLUORINE ATOMS
IN A TUG OF WAR FOR THOSE SHARED ELECTRONS,
THEY'RE GOING TO PULL WITH EQUAL FORCE,
SO THERE ARE NO POLES CREATED.
AND THEN A VERY IMPORTANT COMBINATION,
EVEN THOUGH CARBON AND HYDROGEN HAVE A SLIGHT DIFFERENCE
IN ELECTRONEGATIVITY,
WE CONSIDER THEM NON POLAR AS WELL.
AND EVEN IF WE HAD LIKE A DOUBLE OR A TRIPLE BOND,
NOTICE THAT POLARITY HAS NOTHING
TO DO WITH THE TYPES OF BONDS PRESENT.
ANYTIME WE HAVE A COMPOUND
THAT'S ALL CARBONS AND HYDROGEN'S,
IT'S GOING TO BE NON POLAR,
SO NON POLAR COMPOUNDS ARE KIND OF BORING.
THERE'S REALLY NOT TOO MUCH ELSE TO SAY THERE.
IT'S THE POLAR COMPOUNDS THAT ARE OF INTEREST.
SO THIS IS WHERE WE HAVE AN UNEQUAL SHARING OF ELECTRONS.
AND SO WE SAW THE SYMBOLS EARLIER.
SO WE COULD DESCRIBE IT ONE OF TWO WAYS.
THIS IS CALLED A DIPOLE MOMENT ARROW.
ALL RIGHT.
SO THE ARROW POINTS TO WHERE THE ELECTRONS WANT TO GO.
SO THAT'S WHERE THE PARTIAL NEGATIVE SHOWS UP
AND THEN THERE'S A CROSSHATCH
ON THE SHAFT OF THE ARROW TO LOOK LIKE A PLUS SIGN
AND THIS TELLS US WHERE THE ELECTRONS ARE MISSING.
SO WE COULD USE EITHER ONE OF THESE SYMBOLS.
WE COULD EITHER USE THE DIPOLE MOMENT ARROW
OR WE COULD USE THE PARTIAL POSITIVE AND PARTIAL NEGATIVE
TO INDICATE WHEN WE HAVE A POLAR COVALENT BOND.
AND SO THIS IS WHERE WE HAVE, RIGHT,
THIS IS WHERE WE HAVE A DIFFERENCE
IN ELECTRONEGATIVITY.
SO WHEN WE LOOK AT THESE EXAMPLES, RIGHT,
THE FIRST THING WE WANT TO DO IS PRACTICE OUR TREND.
SO IF WE LOOK HERE,
IF WE HAVE CARBON AND OXYGEN--
I'LL JUST DRAW A PERIODIC TABLE RIGHT HERE. OKAY.
AND THEN HERE'S OUR BUDDY, HYDROGEN. OKAY.
SO IF WE HAVE CARBON AND OXYGEN, RIGHT?
BASED OFF OF ELECTRONEGATIVITY, RIGHT,
ELECTRONEGATIVITY INCREASES TO THE RIGHT.
SO WE WOULD WRITE OUR DIPOLE MOMENT ARROW POINTING
TOWARDS OXYGEN BECAUSE IT'S MORE ELECTRONEGATIVE.
OR WE COULD WRITE A PARTIAL PLUS ON THE CARBON
AND A PARTIAL MINUS ON THE OXYGEN.
ALL RIGHT.
SO THEN CHLORINE IS DOWN HERE,
SO IF WE HAD CARBON AND CHLORINE--
THIS ONE MIGHT FEEL A LITTLE TRICKY
BUT NOTICE WE'RE GOING THREE ELEMENTS
TO THE RIGHT AND WE'RE ONLY GOING ONE ELEMENT DOWN.
SO CHLORINE IS MORE ELECTRONEGATIVE THAN CARBON.
SO ONCE AGAIN, THE DIPOLE MOMENT ARROW IS POINTING TO THE RIGHT.
BUT THERE'S NO RULE HOW THE DIPOLE MOMENT ARROWS WILL POINT.
OXYGEN, RIGHT?
HYDROGEN ALWAYS LOSES.
HYDROGEN ONLY HAS ONE PROTON, SO IT DOESN'T HAVE A LOT
OF POWER TO ATTRACT THE SHARED ELECTRONS.
SO THE DIPOLE MOMENT ARROW IS GOING TO POINT
TOWARD THE OXYGEN,
LETTING US KNOW THAT THE--
BECAUSE OXYGEN IS MORE ELECTRONEGATIVE,
THE SHARED ELECTRONS SPEND MORE TIME WITH OXYGEN
AND LESS TIME WITH HYDROGEN,
CREATING THESE POLES OF ELECTROSTATIC CHARGE.
NOW, ONE THING THAT CAN BE A LITTLE BIT CONFUSING
ABOUT THESE DIPOLE MOMENT ARROWS AND THESE PARTIAL PLUS
AND MINUSES IS WE HAVEN'T PUT AN ACTUAL NUMERICAL VALUE.
BUT ALL POLAR BONDS, RIGHT,
WE SAW ON THE PAGE BEFORE THAT THERE
CAN BE A RANGE OF POLARITIES.
SO LET'S LOOK HERE AT THIS TYPE OF QUESTION.
ARRANGE THE FOLLOWING BONDS
IN THE ORDER OF DECREASING POLARITY.
NOW, THIS TYPE OF QUESTION IT'S ONLY REASONABLE
TO ASK IT IF WE KEEP ONE ATOM THE SAME, RIGHT?
SO HERE'S OUR BUDDY, CARBON.
AND THEN WE'RE LOOKING AT HOW CARBON IS BONDING TO NITROGEN,
OXYGEN, AND FLUORINE, RIGHT?
SO THE GREATER THE DISTANCE
BETWEEN TWO ELEMENTS IN THE PERIODIC TABLE,
THE GREATER THE DIFFERENCE IN THE ELECTRONEGATIVITY.
SO IF WE'RE GOING FOR DECREASING POLARITY,
WE WANT TO HAVE THE MOST POLAR.
AND THE MOST POLAR MEANS THE LARGEST, RIGHT,
DIFFERENCE IN ELECTRONEGATIVITY,
THE DELTA SYMBOL MEANS DIFFERENCE. OKAY.
AND THEN WE'RE GOING TO DECREASE
TO THE LEAST POLAR.
ALL RIGHT.
SO LOOKING AT THESE ELEMENTS,
CARBON AND FLUORINE ARE THE FARTHEST OF--
OOPS, THERE WE GO.
CARBON AND FLUORINE ARE THE FARTHEST APART,
SO THEY'RE GOING TO BE THE MOST POLAR.
THEN WOULD COME THE CARBON-OXYGEN BOND
AND THEN WOULD COME THE CARBON-NITROGEN.
SO THIS WOULD BE THE LEAST POLAR.
ALL RIGHTY.
NOW, THESE ARE IMPORTANT SKILLS,
RECOGNIZING POLARITY AND UNDERSTANDING ELECTRONEGATIVITY.
BUT THIS IS A TOOL TO HELP US UNDERSTAND MOLECULES BETTER.
SO NOW THAT WE RECOGNIZE THE TRENDS IN ELECTRONEGATIVITY,
LET'S APPLY THEM TO ENTIRE MOLECULES.
SO FOR MOLECULAR POLARITY,
THIS IS GOING TO DEPEND ON TWO FACTORS,
THE MOLECULAR SHAPE AND THE--
AND THEN THE BOND POLARITY.
OKAY. SO MOLECULAR SHAPE,
THIS WOULD BE THE THREE-DIMENSIONAL SHAPE
AND THERE'S A VIDEO TUTORIAL AVAILABLE ON MOLECULAR SHAPE
AND THIS USES THE VALENCE SHELL ELECTRON PAIR REPULSION THEORY.
SO IF YOU'RE FEELING UNCOMFORTABLE
WITH ME TALKING ABOUT MOLECULAR SHAPE AND VSEPR THEORY,
YOU'LL WANT TO GO AND REVIEW THE VIDEO TUTORIAL
ON THIS TOPIC.
AND THEN FOR BOND POLARITY, THIS WILL BE THE DIFFERENCES
IN ELECTRONEGATIVITY WHICH WE'VE TALKED--
BEEN TALKING ABOUT IN THE FIRST COUPLE PAGES.
SO, WE'RE GOING TO TAKE EVERYTHING
WE'VE JUST LEARNED ABOUT BONDS
AND NOW APPLY IT IN THREE DIMENSIONAL SPACE.
SO, A NON POLAR MOLECULE IS JUST LIKE A NON POLAR BOND,
THERE'S NO DISTRIBUTION OF CHARGE
OR IT'S SYMMETRICAL AND BALANCED VERSUS A POLAR MOLECULE,
RIGHT, ASYMMETRICAL MEANS
NOT SYMMETRICAL DISTRIBUTION OF CHARGE.
SO LET'S WORK OUR WAY THROUGH BIGGER AND BIGGER MOLECULES
TO SEE HOW THIS APPLIES.
TWO ATOM MOLECULES ARE VERY SIMPLE,
IT'S THE SAME AS BOND POLARITY, RIGHT.
SO EVEN IF WE HAVE TWO--
NOW I PUT THE VALENCE ELECTRONS
IN HERE OR THE LONE PAIRS, RIGHT?
SO EVEN IF YOU HAD TWO FLUORINES
WHICH ARE THE MOST ELECTRONEGATIVE,
THIS IS STILL NON POLAR AND IF WE HAVE--
IF WE REPLACE THIS WITH FOR EXAMPLE WITH HYDROGEN,
NOW WE CAN DRAW IN OUR DIPOLE MOMENT
OR THE DIPOLE MOMENT ARROW
OR WITH OUR PARTIAL PLUS AND OUR PARTIAL MINUS.
AND SO ANYTIME WE HAVE A MOLECULE WITH ONLY
ONE DIPOLE MOMENT ARROW,
WE RECOGNIZE THIS AS A POLAR MOLECULE.
ALL RIGHT.
SO NOW LET'S GETS TO SOME TRICKIER ONCE.
WHAT HAPPENS IF WE HAVE THREE ATOMS IN A MOLECULE?
WELL, LET'S LOOK AT CARBON DIOXIDE, RIGHT.
ON THE PREVIOUS PAGE,
WE NOTED THAT CARBON AND OXYGEN HAVE DIFFERENCES
IN ELECTRONEGATIVITY,
SO WE DO HAVE POLAR BONDS HERE.
HOWEVER, THIS DIPOLE MOMENT IS EQUAL
AND OPPOSITE TO THIS DIPOLE MOMENT SO THEY CANCEL OUT.
SO EVEN THOUGH WE HAVE POLAR BONDS PRESENT,
WE END UP WITH A BALANCED--
OOPS, LET ME SLIDE THIS DOWN.
WITH A SYMMETRICAL BALANCE DISTRIBUTION OF CHARGE.
SO, FOR CO2, IT'S NON POLAR.
BUT WE COULD HAVE--
LET'S LOOK AT OZONE, RIGHT.
WHEN WE DO OZONE,
WE NOW HAVE A BENT MOLECULE.
AND SO ANYTIME--
IT'S PRETTY SIMPLE, ANYTIME OUR CENTRAL ATOM HAS A LONE PAIR,
WE KNOW IT'S GOING TO BE POLAR BUT LET'S--
BUT INSTEAD OF JUST MEMORIZING SOMETHING BLINDLY,
LET'S REASON IT OUT. OH.
WELL PLUS-- YEAH.
SO EVEN THOUGH THESE ARE ALL OXYGENS,
THE LONE PAIR IS GOING TO PULL
AND THAT'S GOING TO CREATE POLARITY.
I THINK I LIKE TO DO A COUPLE MORE EXAMPLES HERE.
ANOTHER COMMON EXAMPLE IS SULFUR DIOXIDE,
OOPS, TOO MANY LONE PAIRS.
THERE WE GO. OKAY.
SO WHEN WE HAVE THIS BENT ARRANGEMENT,
THE OXYGEN PULLS THE ELECTRONS
AND NOTICE THAT NOW THEY'RE PULLING--
THEY'RE NOT CANCELLING BECAUSE THEY'RE AT ANGLES TO EACH OTHER,
SO IT'S ALSO POLAR.
ANOTHER TRICK THAT WE CAN USE WHEN WE'RE TRYING TO DETERMINE
MOLECULAR POLARITY IS WE CAN TAKE THE DIPOLE MOMENT ARROWS
AND PUT THEM--
WE CALL THIS THE TIP AND THE TAIL.
FOR EXAMPLE IF WE LOOK AT CARBON DIOXIDE,
WE HAVE ONE ARROW GOING TO THE RIGHT
AND THEN THE SECOND ARROW IS GOING TO THE LEFT
AND WE'RE BACK WHERE WE STARTED, NON POLAR.
IF WE COMPARE THAT TO SULFUR DIOXIDE--
I'LL DO THIS ONE--
WE DO THIS ONE IN GREEN,
RIGHT, SO I DO THE RED ARROW
AND NOW FROM THE TIP OF THE RED ARROW,
I DRAW THE GREEN ARROW.
NOW WE SEE THAT WE HAVE ENOUGH DIPOLE
THAT WE DIDN'T GET BACK TO THE BEGINNING.
SO WHEN WE-- ANYTIME, WE HAVE A NET RESULT,
THAT'S WHY IT'S CONSIDERED POLAR.
ALL RIGHTY.
LET'S KEEP BUILDING UP TO SOME BIGGER MOLECULES,
IF WE HAVE FOUR ATOMS IN A MOLECULE,
FOR EXAMPLE HERE, WE HAVE THIS COMPOUND.
IF WE'RE LOOKING AT THE CARBON,
REMEMBER THAT THE CARBONS AND THE HYDROGEN SHARE
EQUALLY SO WE DON'T HAVE TO WORRY ABOUT DRAWING
IN ANY DIPOLE MOMENT ARROWS HERE.
HOWEVER, SULFUR IS MORE ELECTRONEGATIVE THAN CARBON
SO WE WILL GET A DIPOLE THERE.
THIS IS A SIMPLE ONE.
ANYTIME WE DRAW A POLAR--
WE DRAW ONLY ONE DIPOLE MOMENT ARROW,
WE KNOW THE MOLECULE IS POLAR.
AND, OH, OKAY.
AND THEN ANOTHER EXAMPLE WOULD BE FOR EXAMPLE,
WE DID LIKE AMMONIA.
SO IT HELPS TO DRAW IT IN ITS THREE-DIMENSIONAL SHAPE, RIGHT?
SO WHEN WE LOOK AT AMMONIA,
REMEMBER THAT THE WEDGE IS POKING OUT
AT US AND THE DASH IS GOING BACK AND THEN
I REMEMBER I'LL DIRECT YOU TO THE MOLECULAR GEOMETRY,
MOLECULAR SHAPED TUTORIAL IF THESE PART'S FUZZY FOR YOU.
AND NOW, WE KNOW NITROGEN IS MUCH MORE ELECTRONEGATIVE
SO THERE'S A DIPOLE MOMENT ARROW AND I'M GOING TO DO
EACH DIPOLE MOMENT ARROW WITH A DIFFERENT COLOR
BUT NOTICE THAT THEY'RE ALL POINTING UP
AND THEN WE DO GET A BIT OF A PULL FROM THE LONE PAIR.
SO, BECAUSE OF THE TRIGONAL PYRAMIDAL SHAPE
AND ALL OF THE DIPOLE MOMENT ARROWS POINTING UP,
THEY'RE ALL POINTING IN THE SAME DIRECTION
SO THAT'S GOING TO BE ANOTHER EXAMPLE
OF A POLAR MOLECULE.
AND THEN TO CONVINCE YOU, LET'S TRY IF WE DO-- RIGHT,
THERE'S THE RED ARROW AND THEN IF WE PUT--
ADD THE BLUE AND THEN THE GREEN,
RIGHT, NOTICE THAT WE END UP WITH A NET DIPOLE FOR AMMONIA,
SO IT'S A POLAR COMPOUND.
IT IS POSSIBLE FOR THERE TO BE NON POLAR COMPOUNDS,
LET ME SHOW YOU ONE OF THOSE.
IF WE HAD SULFUR TRIOXIDE,
REMEMBER THAT THE DOUBLE
AND SINGLE BONDS DO NOT AFFECT THE POLARITY.
THIS IS SIMPLY ABOUT THE IDENTITY OF THE ATOMS.
SO HERE'S THE EXAMPLE
WHERE WE WOULD HAVE THREE DIPOLE MOMENT ARROWS ALL PULLING OUT,
RIGHT, BUT THEY'RE ALL EQUAL
IN SIZE SO WE HAVE EQUAL DIPOLE MOMENTS,
RIGHT, AND THEN THE GEOMETRY HERE IS TRIGONAL PLANAR.
SO, THIS IS SIMILAR TO CARBON DIOXIDE,
IT'S LIKE THREE SPOKES
ON A WHEEL PULLING WITH EQUAL INTENSITY,
SO THEY ALL CANCEL OUT AND THE MOLECULE IS NON POLAR.
ALL RIGHTY.
ONE LAST--
WE'LL ONLY GO UP TO FIVE ATOM MOLECULES.
SO HERE, THIS WOULD TEND TO BE OUR TETRAHEDRAL ARRANGEMENTS,
SO THIS IS WHERE IT CAN BE VERY IMPORTANT
TO REMEMBER THE THREE-DIMENSIONAL SHAPE
BECAUSE IF WE LOOK AT THIS MOLECULE HERE
AND WE WROTE OUT OUR DIPOLE MOMENTS,
WE MAY VERY NAIVELY THINK THAT THESE TWO DIPOLE MOMENTS ARE
GOING TO CANCEL,
SO IT'S IMPORTANT TO SEE THE 3D SHAPE,
RIGHT, IT'S TETRAHEDRAL.
SO WHEN WE DRAW THIS MOLECULE,
WE NEED TO DRAW IT SO THAT WE ARE REMINDED
OF THAT THREE-DIMENSIONAL SHAPE, RIGHT?
SO THE CHLORINES ARE NOT, RIGHT,
THIS IS NOT A SQUARE,
FLAT MOLECULE, THE ATOMS AROUND THE CARBON ARE RADIATING
OUT INTO THE CORNERS OF THE TETRAHEDRON.
AND SO NOW WHEN WE DRAW OUR DIPOLE MOMENT ARROWS,
WE SEE THAT THEY'RE PULLING IN THE SAME DIRECTION,
ANYTIME OUT DIPOLE MOMENT ARROWS ARE PULLING
IN THE SAME DIRECTION IT CREATES A NET DIPOLE.
AND SO THIS WOULD BE A POLAR MOLECULE.
OF COURSE, IF WE TAKE AND WE HAVE ALL FOUR ATOMS AS CHLORINE,
NOW WE'RE BACK TO THE SYMMETRICAL CHARGE DISTRIBUTION.
NOW, WE HAVE-- WE--
THIS IS JUST LIKE CARBON DIOXIDE,
WE HAVE FOUR POLAR BONDS
BUT THESE FOUR POLAR BONDS ARE ALL PULLING TO THE CORNERS
OF THE TETRAHEDRON.
AND SO WE END UP WITH A NON POLAR MOLECULE.
ALL RIGHTY.
SO NOW LET'S DO A LITTLE BIT OF PRACTICE TO MAKE--
SEE HOW YOU'RE DOING HERE.
SO HERE ARE FOUR PRACTICE MOLECULES
FOR YOU TO MAKE PREDICTIONS ABOUT THE POLARITY.
SO THIS FIRST MOLECULE HERE,
RIGHT, ALL CARBONS AND HYDROGENS
ANYTIME IT'S ALL CARBONS AND HYDROGENS, NON POLAR.
NOW, WE'VE REPLACED TWO OF THE HYDROGENS WITH CHLORINES.
HERE WE NOTICE, RIGHT,
THAT BOTH OF THE CHLORINES ARE PULLING IN THE SAME,
RIGHT, THEY'RE BOTH PULLING TO THE RIGHT
SO THAT CREATES THE NET DIPOLE.
SO THIS WILL BE A POLAR MOLECULE.
LET'S SEE WHAT HAPPENS IF WE MOVE
THESE CHLORINE ATOMS AROUND.
NOW THE CHLORINE ATOMS ARE
COMING OFF OF TWO SEPARATE CARBON ATOMS,
BUT ONCE AGAIN THEY'RE PULLING IN THE SAME DIRECTION.
SO WE'RE GOING TO END UP WITH A POLAR MOLECULE.
AND THEN LAST BUT NOT LEAST, NOW WE HAVE THE CHLORINES
ON OPPOSITE SIDES OF THIS DOUBLE BOND,
NOW NOTICE IT'S THE SAME SIZE DIPOLE EQUAL AND OPPOSITE,
SO IT CANCELS TO CREATE A NON POLAR MOLECULE.
ALL RIGHTY.
SO I HOPE THAT YOU FOUND THIS TUTORIAL HELPFUL,
AND THAT YOU'LL TAKE THE TIME TO WORK SOME HOMEWORK PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.