- WELCOME TO THE VIDEO TUTORIAL ON IONIC COMPOUNDS,
FORMULA UNITS AND NOMENCLATURE.
SO THIS IS A VERY IMPORTANT FUNDAMENTAL CONCEPT
THAT WILL BUILD OFF OF OUR UNDERSTANDING OF IONS, RIGHT.
SO WE KNOW THAT IONS OCCURRED BECAUSE ATOMS
CAN GAIN OR LOSE ELECTRONS TO BECOME IONS.
SO CATION, THAT IS THE TERM TO DESCRIBE--
I'LL LEAVE A PAUSE THERE FOR YOU TO FILL IN THE BLANK,
RIGHT, THAT WOULD BE A POSITIVE ION AND THEN ANIONS,
OF COURSE, ARE NEGATIVE IONS.
SO IF YOU'RE HAVING TROUBLE KEEPING THIS STRAIGHT,
REMEMBER THAT THE T IN CATION RESEMBLES THE PLUS SIGN
SO THAT REMINDS THAT CATIONS ARE POSITIVE
AND THEN ANIONS WITH THAT N THERE ARE NEGATIVE.
AND SO WHEN WE HAVE A NEUTRAL ATOM, THERE IS NO CHARGE.
REMEMBER THAT WHEN WE HAVE A CATION FORMING
OR AN ANION FORMING,
THAT THE TOP RIGHT CORNER,
THE RIGHT SUPERSCRIPT IS WHERE WE INDICATE THE CHARGE ON--
WHEN AN ELEMENT WHEN IT IS IN ITS IONIC FORM. OKAY.
NOW, THE OCTET RULE FOR IONIC BONDS IS WHERE ATOMS
WILL GAIN OR LOSE ELECTRONS
TO ACHIEVE A FULL VALENCE SHELL OF EIGHT ELECTRONS.
SO IF THE ATOMS ARE GAINING ELECTRONS,
THEY BECOME AN ANION AND IF THEY LOSE ELECTRONS,
THEY BECOME A CATION, RIGHT?
SO IT'S THAT KIND OF COUNTERINTUITIVE EFFECT
WE HAVE BECAUSE ELECTRONS ARE NEGATIVE, RIGHT.
SO CATIONS FORM BY LOSING ELECTRONS AND ANIONS FORM
BY GAINING ELECTRONS.
AND THEN IF WE TIE THIS TO OUR UNDERSTANDING
OF THE PERIODIC TABLE WITH THE STAIR-STEP LINE,
RIGHT, SO IF WE LOOK AT THE PERIODIC TABLE,
WE SHOULD ALWAYS SEE THE STAIR-STEP LINE, RIGHT?
THAT SEPARATES THE METALS FROM THE NONMETALS.
ALL RIGHT.
AND SO THAT--
IT HELPS US TO PREDICT THE TYPE OF IONS THAT WERE FORM.
METALS LIKE TO LOSE ELECTRONS TO FORM CATIONS.
NONMETALS ARE LIKE TO GAIN ELECTRONS TO FORM ANIONS.
NOW, THESE IONS COME TOGETHER TO CREATE NEUTRAL SALTS,
SO IONIC COMPOUNDS ARE ALSO DESCRIBED AS SALTS,
AND THAT'S ONE OF THOSE THINGS
THAT JUST TENDS TO SLIDE INTO CHEMISTRY CLASSES
WITHOUT A FORMAL INTRODUCTION.
SO I WILL LIKE TO FORMALLY INTRODUCE YOU TO IONIC COMPOUNDS
WHEN THEY'RE DESCRIBED AS NEUTRAL SALTS, RIGHT?
SO THE CATION CHARGE IS GOING TO--
POSITIVE CHARGE IS GOING TO BE ATTRACTED TO THE ANION AND SO--
I DON'T LIKE THE WAY I DREW THAT,
RIGHT, SO THEY'RE GOING TO BE ATTRACTED TO EACH OTHER
AND SO THAT'S WHAT'S GOING TO CREATE THE CRYSTAL LATTICE.
NOW, THE IMPORTANT THING HERE IS THAT WE HAVE TO MAKE SURE
THAT THE TOTAL POSITIVE CHARGE IS EQUAL
TO THE TOTAL NEGATIVE CHARGE.
AND SO THAT IS HOW WE CREATE THE CHEMICAL FORMULAS
FOR IONIC COMPOUNDS.
TO CREATE ANY CHEMICAL FORMULA IS WE HAVE TO FIGURE OUT
THE RATIO OF THE IONS SO THAT OUR TOTAL
POSITIVE CHARGE EQUALS OUR TOTAL NEGATIVE CHARGE.
SO, FOR EXAMPLE,
LET'S SAY WE HAD A MAGNESIUM ION WHICH IS PLUS 2
AND A CHLORIDE ION THAT'S MINUS 1. HERE,
WE HAVE A TOTAL POSITIVE CHARGE
OF PLUS 2. CHLORIDE ONLY HAS THE ABILITY TO BRING IN
A MINUS 1 SO WE ARE GOING TO NEED 2 CHLORIDE IONS
TO CREATE AN OVERALL NEGATIVE 2 CHARGE SO
WHEN WE WRITE THE CHEMICAL FORMULA FOR THIS IONIC COMPOUND,
IT WILL BE MAGNESIUM WITH CO2.
NOW IT'S IMPORTANT
TO NOTE THAT WHEN WE WRITE THE CHEMICAL FORMULA,
NOTICE THAT WE DO NOT SHOW THE CHARGE OF THE IONS.
WE SIMPLY--
AND SO WE USE THE BOTTOM RIGHT CORNER,
THE RIGHT SUBSCRIPT TO SHOW THE RATIO.
WE NEVER SHOW THE 1S SO THIS IS UNDERSTOOD TO BE A 1:2 RATIO,
1 MAGNESIUM TO 2 CHLORIDE IONS,
THEY WILL BE ATTRACTED TO EACH OTHER ELECTRO--
ELECTROSTATICALLY.
THEY WILL CREATE A CRYSTAL LATTICE
FOR THE SOLID MAGNESIUM CHLORIDE.
NOW, THE USEFUL THING
OR HELPFUL THING ABOUT IONIC COMPOUNDS IS NAMING
FOLLOWS THE SAME PATTERN AS THE CHEMICAL FORMULA.
WE ARE ALWAYS GOING TO HAVE THE CATION
FIRST FOLLOWED BY THE ANION WHICH IS SECOND.
AND THE NAMES ARE A BIT OF A PUZZLE.
ALL WE NEED TO KNOW IS WHICH IONS ARE PRESENT
AND THEN IT'S A PUZZLE THAT WE CAN FIGURE OUT
THE RATIO TO CREATE THE NEUTRAL COMPOUND.
SO LET'S PRACTICE THIS SKILL TOGETHER.
ALL RIGHT.
WITH OUR FIRST EXAMPLE, WE HAVE POTASSIUM AND BROMIDE.
THIS IS A VERY STRAIGHTFORWARD EXAMPLE BECAUSE WE HAVE PLUS 1
AND MINUS 1. SO WE ALREADY ARE CREATING A NEUTRAL COMPOUND
WITH A 1:1 RATIO.
SO WE LIST OUR CATION FIRST AND OUR ANION SECOND
AND THE NAME OF THIS CATION IS POTASSIUM.
AND THE NAME OF THIS ANION IS BROMIDE.
ALL RIGHT.
OH, NOW HERE'S MAGNESIUM'S BACK FOR AN ENCORE, RIGHT,
MAGNESIUM GIVES US A +2 CHARGE.
EACH OF THE HYDROXIDE ION IS ONLY MINUS 1.
TO CREATE A NEUTRAL COMPOUND,
WE ARE GOING TO NEED TO HAVE 2 HYDROXIDES
SO THAT WE HAVE A PLUS 2
AND A MINUS 2. SO THAT TELLS THAT THE RATIO
HERE IS GOING TO BE 1:2.
WE WILL HAVE 1 MAGNESIUM.
NOW WITH POLYATOMIC IONS,
ANYTIME WE HAVE MORE THAN ONE OF A POLYATOMIC ION,
WE ENCLOSED ITS FORMULA IN PARENTHESES,
SO THERE IS OUR 1:2 RATIO.
THE NAME IS VERY STRAIGHTFORWARD.
THE NAME OF THIS ION IS MAGNESIUM.
AND THE NAME OF THIS ANION IS HYDROXIDE.
SO NOTICE THAT THIS WORKS,
IF WE JUST READ THE NAME MAGNESIUM HYDROXIDE,
WE WOULD KNOW MAGNESIUM IS 2 PLUS AND HYDROXIDE IS MINUS 1
AND BECAUSE OF OUR UNDERSTANDING OF CHEMISTRY,
WE WOULD KNOW THAT THESE IONS MUST COME TOGETHER
IN A 1:2 RATIO TO CREATE THE NEUTRAL COMPOUND.
ALL RIGHTY.
LET'S LOOK AT ANOTHER EXAMPLE.
HERE, WE HAVE IRON 2 SO REMEMBER THAT IRON IS A TRANSITION METAL
AND IT HAS THE ABILITY TO FORM MORE THAN ONE OXIDATION STATE.
SO THE NAME OF THIS ION IS IRON II.
ALL RIGHT.
SO WE HAVE A PLUS 2 COMING FROM THE IRON.
AND THEN WE HAVE PHOSPHATE
WHICH IS A MINUS 3. SO NOW WE NEED TO BRING THESE IONS
TOGETHER IN A RATIO THAT WILL CREATE A NEUTRAL COMPOUND.
AT THIS POINT, IT CAN BE VERY HELPFUL
TO THINK ABOUT THE MULTIPLES, RIGHT?
WE WANT TO FIND THE LEAST COMMON MULTIPLE.
SO THE IRON 2 CAN ONLY COME IN IN INCREMENTS
OF PLUS 2. THE PHOSPHATE CAN ONLY COME IN IN INCREMENTS
OF MINUS 3. SO WE CAN SEE THAT THE LEAST COMMON MULTIPLE
WOULD BE 6. WE ARE GOING TO NEED 3 IRON 2S TO CREATE A PLUS 6
THAT WILL BALANCE TWO PHOSPHATES CREATING A MINUS 6
SO THAT WE CAN ACHIEVE A NEUTRAL COMPOUND SO
THERE IS OUR IRON 2. WE'RE GOING TO NEED 3 OF THOSE AND THEN
WE WOULD HAVE OUR PHOSPHATE AND WE'RE GOING TO NEED 2
OF THOSE SO THERE IS OUR CHEMICAL FORMULA
SO HERE IS THE CHEMICAL FORMULA FOR THE COM--
FOR THE COMPOUND,
IRON
(II)
PHOSPHATE.
THIS CAN BE VERY CONFUSING.
SOMETIMES PEOPLE COULD THINK THAT THE ROMAN NUMERAL
IS TELLING US THE NUMBER OF IRON IONS
IN THE COMPOUND AND THAT IS NOT CORRECT.
REMEMBER THAT THE IRON
(II)
IS TELLING US WE HAVE IRON PLUS IN OUR FORMULA.
ALL RIGHTY.
SOMETIMES PEOPLE LIKE TO USE THE CRISSCROSS METHOD SO
FOR EXAMPLE WITH THE IRON 2 AND THE PHOSPHATE,
WE COULD CRISSCROSS THE CHARGES OVER
AND GET THE ANSWER THAT WE SEE RIGHT HERE.
AND IN MANY CASES,
THE CRISSCROSS METHOD WORKS GREAT.
BUT HERE'S AN EXAMPLE WHERE IT DOESN'T WORK.
IF WE TRY TO USE THE CRISSCROSS METHOD HERE,
WE HAVE LEAD 4 AND REMEMBER LEAD IS A--
IS AN ELEMENT THAT HAS MORE THAN ONE OXIDATION STATES
SO WE HAVE TO INCLUDE THE ROMAN NUMERAL
AND THEN THERE'S OUR BUDDY, CARBONATE.
SO IN THIS CASE, IF WE TRIED TO USE THE CRISSCROSS METHOD,
WE WOULD END UP WITH--
I'LL JUST DO IT IN RED.
WE WOULD END UP WITH 2 PHOSPHATES
AND 4 CARBONATES NOW THIS IS NOT
A CORRECT CHEMICAL FORMULA. WHY?
BECAUSE WE ALWAYS WANT TO HAVE THE SMALLEST RATIO
OF WHOLE NUMBERS AND SO HERE
WE CAN SEE THAT THERE IS A MULTIPLE OF TWO.
SO WE WOULD WANT TO REDUCE THIS TO--
THERE'S GOING TO BE 1 LEAD 4 AND 2 CARBONATES.
SO IF YOU DECIDE TO USE THE CRISSCROSS METHOD,
MAKE SURE TO LOOK AT YOUR RATIO
FOR COMMON FACTORS THAT CAN BE REDUCED.
THE OTHER WAY TO DO IT IS TO THINK ABOUT MULTIPLES
AND WE HAVE LEAD 4+
AND CARBONATE 2- SO THE LEAST COMMON MULTIPLE WILL BE 4.
SO THAT TELLS US THAT WE ONLY NEED 1 LEAD
BUT WE WILL NEED 2 CARBONATES, RIGHT?
SO WE'LL DRAW THIS OUT ONE MORE TIME.
YUP, SO I GUESS WE'LL JUST DRAW IT HERE, RIGHT?
SO IT WOULD TAKE 1 LEAD TO MAKE PLUS 4 AND 2 CARBONATES
TO MAKE MINUS 4. SO WE WOULD STILL END UP
WITH THE SAME CHEMICAL FORMULA
AND THEN MAKING SURE THAT WE'RE GOOD ON OUR ION NAMES.
IT'S SIMPLY LEAD
(IV)
CARBONATE.
ALL RIGHTY. LETS SEE.
AND NOW, WE'LL DO ONE LAST BIT
OF WRAP UP TO SHOW HOW WE CAN USE OUR UNDERSTANDING
OF THE CHEMICAL FORMULAS AND NOMENCLATURE OF IONIC COMPOUNDS
AND THEN WE CAN APPLY IT TO SOLUTION CHEMISTRY.
SO IN OUR LAST PAGE HERE,
IONIC COMPOUNDS ARE SOLIDS IN PURE STATE.
THE IONS ARE LOCKED TOGETHER IN THE CRYSTAL LATTICE CREATING--
CREATED BY THE CATIONS
AND ANIONS MAXIMIZING THEIR ATTRACTED FORCES
AND MINIMIZING THEIR REPULSIVE FORCES.
SO THEN LET'S KEEP IN MIND WHAT HAPPENS TO IONIC COMPOUNDS
WHEN THEY DISSOLVE IN WATER.
SO LET'S TAKE AN EXAMPLE LIKE SODIUM CARBONATE.
SO THIS IS AN EXAMPLE OF SODIUM CARBONATE.
HERE IT IS AS A SOLID.
SO THEN REMEMBER THAT IF WE ADD THIS TO WATER, RIGHT?
THE WATER IS GOING TO PULL APART THE SODIUM IONS
AND THE CARBONATE IONS THROUGH INTERMOLECULAR FORCES
AND IF YOU WANT A REVIEW OF THAT,
THERE IS A TUTORIAL THAT TALKS ABOUT INTERMOLECULAR FORCES
WITH SOLUTION FORMATION AND THE IMPORTANT THING
TO REMEMBER IS THAT WHEN WE ADD THE SODIUM CARBONATE
TO THE WATER AND IT DISSOLVES,
THOSE SODIUM IONS BECOME INDEPENDENT
FOR EVERY FORMULA UNIT OF SODIUM CARBONATE.
WE WILL RELEASE TWO SODIUM IONS AND 1 CARBONATE ION
AND SO FOR IONIC COMPOUNDS IN PARTICULAR,
WE GO FROM A SINGLE COMPOUND TO THREE INDEPENDENT SOLUTE IONS.
ALL RIGHTY.
SO AS YOU'RE WORKING WITH THE IONIC COMPOUNDS REMEMBER
TO KEEP THE IDEA OF THEIR RATIO IN YOUR MIND SO LET'S PREDICT
HOW MANY IONS ARE RELEASED INTO AN AQUEOUS SOLUTION
WHEN ONE FORMULA UNIT IS DISSOLVED IN WATER
AND LET'S GO AHEAD AND WRITE OUR ANSWERS
LIKE A CHEMICAL REACTION.
SO WE'RE STARTING WITH POTASSIUM PHOSPHATE
AND THEN WE'RE GOING TO DISSOLVE IT IN WATER
AND SO WE SEE THAT WE HAVE A RATIO OF 3 POTASSIUMS
TO 1 PHOSPHATE SO THIS WOULD CREATE 3 POTASSIUM IONS
AND 1 PHOSPHATE ION.
ALL RIGHT.
SO NOW WE'LL WORK A FEW MORE EXAMPLES TOGETHER
TO HAVE YOU FEEL CONFIDENT
AS YOU APPROACH YOUR HOMEWORK SO ONCE AGAIN,
THIS WOULD BE SODIUM ACETATE.
IT'S ALSO A SOLID
THAT WE CAN DISSOLVE IN WATER SO HERE WE HAVE A 1:1 RATIO
SO WE WOULD HAVE 1 SODIUM ION DISSOLVED IN WATER
AND 1 ACETATE ION DISSOLVED IN WATER.
SO REMEMBER ALSO THAT, RIGHT,
WHEN WE TALKED ABOUT THE IONS INDEPENDENTLY,
IT'S IMPORTANT TO SHOW THEIR CHARGE
BUT WHEN WE HAVE A COMPOUND,
THE FORMULA UNIT,
THE CHARGES ARE HIDDEN THAT'S WHY YOU'LL SPEND
SO MUCH ENERGY MEMORIZING THEM AND THEN LAST BUT NOT THE LEAST,
HERE WE HAVE A COMPOUND AND THIS IS A GOOD ONE.
HERE WE HAVE COPPER.
WHAT IS THE FORM OF COPPER HERE?
WE WANT--
WE HAVE TO LOOK AT THE ANION, RIGHT?
SO WE KNOW THAT THIS ANION IS NITRATE WITH A MINUS 1
AND WE SEE THAT WE HAVE 2 OF THEM SO THE NET--
ANIONIC CHARGE IS MINUS 2 SO TO CREATE THE NEUTRAL SALT,
WE RECOGNIZE THAT COPPER MUST BE PLUS 2.
SO WHEN WE ADD THIS SOLID TO WATER,
WE WILL HAVE COPPER 2+ AND 2 NITRATE IONS.
SO I THINK JUST TO FINISH UP,
LET'S MAKE SURE THAT WE HAVE ALL OF THE NAMES
FOR THESE IONIC COMPOUNDS SO THIS FIRST COMPOUND HERE
OR THIS COMPOUND HERE WITH COPPER,
THAT WOULD BE COPPER
(II)
NITRATE. THIS WOULD BE SODIUM ACETATE
AND POTASSIUM PHOSPHATE. OKAY.
SO THIS CONCLUDES THE IONIC COMPOUND TUTORIAL
GIVING YOU SOME PRACTICE IN DETERMINING FORMULA UNITS
AND A REVIEW OF THE NOMENCLATURE RULES
AND THEN SOME CONTEXTS FOR HOW YOU'LL USE THIS INFORMATION
AS THE COURSE CONTINUES SO PLEASE TAKE SOME TIME NOW
TO WORK A FEW HOMEWORK PROBLEMS TO REINFORCE YOUR UNDERSTANDING.