- WELCOME TO THE ATOMIC STRUCTURE VIDEO TUTORIAL.
THIS VIDEO TUTORIAL IS REALLY GOING TO FOCUS MORE
ON THE NUCLEUS BUT WE WILL INCLUDE ELECTRONS BRIEFLY.
SO, LET'S REVIEW WHAT WE KNOW ABOUT THE STRUCTURE OF AN ATOM
AND WHAT WE KNOW ABOUT MATTER, RIGHT?
SO, ATOMS ARE THE BASIC BUILDING BLOCKS OF MATTER.
AND IF WE THINK ABOUT OUR DEFINITION OF MATTER, RIGHT,
IT'S ANYTHING WITH MASS AND VOLUME.
SO, ONE OBJECTIVE OF THIS TUTORIAL IS TO MAKE
THAT CONNECTION BETWEEN THE STRUCTURE OF THE ATOM
AND THE MASS AND VOLUME OF MATTER.
SO, THERE ARE THREE SUBATOMIC PARTICLES THAT MAKE UP ATOMS,
THE BASIC BUILDING BLOCKS OF OUR ATOMS,
AND SO AS SOON AS YOU HEAR THOSE WORDS,
THREE SUBATOMIC PARTICLES, THEIR SYMBOLS AND CHARGES
SHOULD BE JUMPING INTO YOUR MIND, RIGHT?
WE HAVE THE PROTON,
WHICH HAS A POSITIVE CHARGE, THE ELECTRON WITH A
-1 CHARGE, AND THEN OF COURSE THE NEUTRON, WHICH IS NEUTRAL.
NOW, I'VE SHOWN THE POSITIVE CHARGE ON THE PROTON HERE,
BUT TYPICALLY, PEOPLE DON'T SHOW THAT CHARGE.
WE'RE JUST SUPPOSED TO KNOW IT'S THERE.
WITH ELECTRONS THOUGH, TRADITIONALLY, MOST PEOPLE DO
PUT THE NEGATIVE CHARGE WITH THEIR ELECTRON SYMBOL.
SO, NOW, IF WE TAKE THESE THREE SUBATOMIC PARTICLES,
LET'S LINK THEM TO MATTER.
WHAT CREATES THE MASS OF MATTER?
AND THAT'S GOING TO BE THE SUBATOMIC PARTICLES
THAT CREATE THE MASS OF THE ATOM.
SO, THAT WILL BE THE PROTONS AND THE NEUTRONS,
WHICH CREATE THE NUCLEUS.
SO THEN, AT THIS POINT,
WHICH SUBATOMIC PARTICLES CREATE THE VOLUME OF AN ATOM?
AND THERE IS ONLY ONE LEFT, AND THAT WOULD BE THE ELECTRON.
TO GIVE YOU A SENSE OF THE PROPORTIONS OF ATOMS,
IF WE TOOK THE NUCLEUS AND WE MADE IT THE SIZE OF A GRAPE,
SO, ALL OF THE MASS
WOULD BE INCLUDED IN THE NUCLEUS FOR THE MOST PART.
THE MASS OF THE ELECTRONS IS BASICALLY NEGLIGIBLE.
ALL OF THE MASS WOULD BE CONCENTRATED IN THAT GRAPE
THAT WE SEE AT THE CENTER.
AND THEN, IF I'M--
SO, IF I'M HOLDING, PLEASE IMAGINE THE NUCLEUS HERE,
THE SIZE OF A GRAPE, ALL OF THE MASSES THERE,
AND THEN THE ELECTRONS ARE
WHIRLING ABOUT UP TO ONE MILE AWAY.
SO, THAT'S ALL THE WAY TO HIGHWAY 99, INTERSTATE
5, BROADWAY TO FRUITRIDGE.
SO, THAT'S CREATING THE VOLUME.
NOTICE THAT THE BULK OF THE ATOM IS STILL EMPTY.
THE MASS IS CONCENTRATED IN THAT NUCLEAR CENTER.
SO, IN DESCRIBING ATOMS, WE TALK ABOUT THE ATOMIC NUMBER.
SO, WHEN YOU HEAR THE WORDS ATOMIC NUMBER,
YOU SHOULD BE VISUALIZING THE SYMBOL Z
AND THINKING ABOUT WHAT PART
OF THE ATOMIC STRUCTURE IS REPRESENTED.
THE ATOMIC NUMBER TELLS US ABOUT THE NUMBER OF PROTONS.
AND THAT'S A GOOD NAME FOR THE NUMBER OF PROTONS
BECAUSE THE NUMBER OF PROTONS,
THAT IS WHAT GIVES US THE IDENTITY OF AN ELEMENT.
IF I'M AN ELEMENT AND MY ATOMIC NUMBER IS SIX,
I HAVE TO BE CARBON.
ANY ELEMENT WITH SIX PROTONS IS CARBON.
IF AN ELEMENT HAS A DIFFERENT NUMBER OF--
OR IF AN ATOM HAS A DIFFERENT NUMBER OF PROTONS,
THEN IT'S GOING TO BE A DIFFERENT ELEMENT.
SO, NOW, THE MASS NUMBER IS RELATED TO THE IDEA
THAT IT'S BOTH THE PROTONS AND THE NEUTRONS
THAT ARE CREATING THE MASS.
SO, WHEN YOU HEAR THE WORDS MASS NUMBER,
YOU'D BE THINKING OF THE SYMBOL "A" AND--
OH, EXCUSE ME.
SO, SLIDE THAT UP, RIGHT?
SO, THERE'S OUR MASS NUMBER.
AND SO, THAT'S GOING TO BE THE NUMBER OF PROTONS
PLUS THE NUMBER OF NEUTRONS, ALL RIGHT?
SO, FOR ANY GIVEN ELEMENT, THE NUMBER OF PROTONS IS FIXED.
HOWEVER, THE NUMBER OF NEUTRONS CAN VARY.
AND SO, IF WE ARE ASKED,
"IS EVERY ATOM OF AN ELEMENT IDENTICAL?"
THE ANSWER WOULD BE NO.
SO, WHEN WE HAVE DIFFERENT ATOMS
OF AN ELEMENT WITH A DIFFERENT NUMBER OF NEUTRONS,
WE DESCRIBE THAT AS AN ISOTOPE.
SO, ISOTOPES EXIST FOR EACH ELEMENT.
OKAY. SO, I'VE ALREADY DESCRIBED ISOTOPES
BUT LET'S LOOK AT THEM A LITTLE MORE CLOSELY.
ALL RIGHT.
SO, WHAT ARE ISOTOPES? RIGHT?
THEY'RE ATOMS OF THE SAME ELEMENT
WITH DIFFERENT NUMBERS OF NEUTRONS.
OKAY. SO, NUMBERS, ALL RIGHTY.
SO, IF WE USE THE LANGUAGE, RIGHT?
THEY HAVE THE SAME Z, ATOMIC NUMBER,
NUMBER OF PROTONS AND DIFFERENT "A,"
MASS NUMBER. ALL RIGHT.
SO, WHEN WE'RE DISTINGUISHING BETWEEN ISOTOPES,
THERE IS A CONVENTION WE USE WITH THE SYMBOLS.
SO, IF I JUST USE E TO REPRESENT ANY ELEMENT,
WE PUT THE ATOMIC NUMBER IN THE LOWER LEFT CORNER
AND THE MASS NUMBER IN THE UPPER RIGHT CORNER, ALL RIGHT?
SO, FOR EXAMPLE,
WE WANTED TO LOOK AT, LIKE,
THE ISOTOPES OF CARBON,
THERE IS CARBON-12 AND CARBON-13.
NOW, IT'S OFTEN ENCOUNTERED THAT WE LEAVE OFF THE ATOMIC NUMBER
BECAUSE IT'S THE SAME FOR ALL THE CARBON ELEMENTS.
THE OTHER OPTION IS WE WRITE THE ELEMENTAL SYMBOL
AND THEN A DASH,
AND THEN WE PUT THE MASS NUMBER FOLLOWING THE ELEMENTAL SYMBOL.
SO, THERE ARE TWO DIFFERENT CONVENTIONS
THAT YOU'LL COMMONLY SEE WHEN ISOTOPES ARE IMPORTANT
IN THE CONVERSATION.
SO, LET'S HAVE A COUPLE OF PRACTICE QUESTIONS
NOW TO MAKE SURE THAT YOU'RE COMFORTABLE
WITH HOW WE DESCRIBE ATOMS,
THE LANGUAGE, AND HOW TO WRITE THE SYMBOLS
FOR VARIOUS ISOTOPES.
ALL RIGHT.
THIS FIRST QUESTION HERE,
"WHAT IS THE MASS NUMBER OF AN ATOM CONTAINING 42 PROTONS,
42 ELECTRONS, AND 47 NEUTRONS? RIGHT?
SO, WE HAVE TO REMEMBER THAT THE MASS NUMBER IS A,
THE NUMBER OF PROTONS PLUS NEUTRONS.
SO, WE'VE BEEN GIVEN SOME INFORMATION
THAT WE REALLY DON'T NEED.
THE ELECTRONS DON'T COME INTO PLAY.
SO, 42 + 47 WOULD GIVE US 89 AS THE MASS NUMBER.
ALL RIGHT.
SO, NOW, IF WE'RE ASKED TO WRITE THE ELEMENTAL SYMBOL
FOR THIS ISOTOPE USING OUR FORMAT,
THE REQUESTED FORMAT HERE, RIGHT?
WE WOULD LOOK AT THE NUMBER OF PROTONS,
WE WOULD LOOK TO OUR PERIODIC TABLE,
AND WE WOULD FIND THE ATOMIC NUMBER Z. AND YOU--
IF YOU LOOK ON YOUR PERIODIC TABLE,
YOU WILL SEE THAT THAT IS ELEMENT MOLYBDENUM.
AND THEN TO--
WE WILL PUT THE ATOMIC NUMBER IN THE LOWER LEFT CORNER,
42, AND THEN OUR MASS NUMBER AT TOP, 89.
SO, AND THEN THE OTHER FORMAT WOULD SIMPLY BE MOLYBDENUM-89.
SO, IT'S GOOD TO BE ABLE TO RECOGNIZE BOTH FORMATS
AND RECOGNIZE THAT THEY'RE NOT ALWAYS GOING TO BE--
ISOTOPES ARE NOT ALWAYS IMPORTANT
TO THE CONVERSATION BUT WHEN THEY ARE,
YOU WANT TO BE ABLE TO UNDERSTAND
WHAT'S BEING SHARED WITH YOU.
ONE LAST EXAMPLE, IODINE HAS AN ATOMIC NUMBER OF 53.
SO, THAT SHOULD SET OFF A FLASH, OH, THERE'S 53 PROTONS.
IODINE-131 IS USED IN THE MEDICAL TREATMENT
OF THYROID CONDITIONS.
HOW MANY NEUTRONS AND PROTONS ARE CONTAINED IN THE NUCLEUS
OF THIS ISOTOPE?
SO, THE FIRST ANSWER IS ALWAYS--
ALREADY BEEN GIVEN TO US.
WE KNOW THE ATOMIC NUMBER IS 53,
SO THAT MEANS THERE'S 53 PROTONS.
NOW, IN THIS FORMAT, 131I,
THAT'S THE MASS NUMBER.
SO, WE KNOW THE MASS NUMBER IS 131,
AND THAT'S THE NUMBER OF PROTONS PLUS THE NUMBER OF NEUTRONS.
SO, IT BECOMES A VERY SIMPLE ALGEBRAIC EXPRESSION
THAT WE HAVE 53 PROTONS,
AND WE'RE TRYING TO FIGURE OUT THE NUMBER OF NEUTRONS.
SO, IT'S SIMPLY 131 - 53. SO,
THERE WOULD BE 78 NEUTRONS AND 53 PROTONS.
ALL RIGHT.
SO, THERE'S ONE LAST PIECE OF ONE ASPECT OF ATOMS
THAT WE SHOULD LOOK AT IN THIS SECTION,
AND THAT HAS TO DO WITH THE CONCEPT
OF THE AVERAGE ATOMIC MASS, ALL RIGHT?
SO, THE AVERAGE ATOMIC MASS
IS HOW WE MATHEMATICALLY DEAL WITH THE FACT
THAT THE ELEMENT HAS A VARIETY OF ISOTOPES.
SO, THE AVERAGE ATOMIC MASS
OF AN ELEMENT IS THE WEIGHTED AVERAGE OF THE MASS
OF AN ELEMENT'S ISOTOPES BASED ON THEIR NATURAL ABUNDANCE.
SO, THE REASON WHY IT HAS TO BE
A WEIGHTED AVERAGE IS BECAUSE WHAT DO YOU THINK?
DO ALL ELEMENTS HAVE THE SAME DISTRIBUTION OF ISOTOPES? NO.
SOME ELEMENTS ONLY HAVE MAYBE TWO MAJOR ISOTOPES.
SOME WILL HAVE FOUR OR FIVE.
AND THE PERCENTAGE OF THIS ISOTOPE VARIES BY ELEMENT.
SO, LET'S LOOK AT SOME EXAMPLES FOR COMPARISON.
LIKE, WE'VE TALKED ABOUT CARBON, CARBON-12 AND CARBON-13.
FOR THIS ELEMENT,
99% IS CARBON-12 AND ONLY 1% IS CARBON-13.
IF WE COMPARE THAT TO CHLORINE, CHLORINE-35,
ONLY 75% OF CHLORINE IS THE CHLORINE-35 ISOTOPE
WITH THE REMAINING 25% AS CHLORINE-37.
SO THERE'S JUST SOME EXAMPLES
SO THAT WE DON'T GET A PRECONCEIVED IDEA
THAT IT'S ALL NICELY BUNDLED FOR US.
AND NOW WE'LL LOOK A LITTLE MORE CLOSELY AT THE ELEMENT CHROMIUM
AND TIE EVERYTHING TOGETHER
THAT WE'VE TALKED ABOUT IN THIS VIDEO, RIGHT?
SO, THE ISOTOPIC DISTRIBUTION FOR CHROMIUM IS SEEN HERE.
THE ATOMIC NUMBER OF CHROMIUM IS 24, SO,
IT'S BEEN LEFT OFF OF THE BOTTOM LEFT CORNER.
NOTICE THE MASS NUMBER IN THE TOP RIGHT CORNER,
AND WE HAVE THE RELATIVE ABUNDANCE
OF THE FOUR STABLE ISOTOPES OF CHROMIUM.
SO, WHICH ISOTOPE IS LIGHTEST?
WELL, RIGHT,
THE LIGHTEST ELEMENT IS GOING TO HAVE THE LOWEST MASS NUMBER,
RIGHT, WHICH IS A. SO, THAT WOULD BE CHROMIUM-50.
WHICH ISOTOPE IS THE MOST ABUNDANT?
WELL, WE JUST SIMPLY LOOK OVER HERE AT THE ABUNDANCE
AND WE SEE THAT CHROMIUM-52 IS DEFINITELY THE MOST ABUNDANT.
WHICH ISOTOPE HAS THE LARGEST NUMBER OF NEUTRONS?
SO-- BECAUSE THE ATOMIC NUMBER IS FIXED,
THE LARGEST NUMBER OF NEUTRONS
WILL BE THE ELEMENT WITH THE LARGEST MASS NUMBER.
SO, WE SEE HERE WITH CHROMIUM-54,
THAT THERE ARE THE 24 PROTONS PLUS NEUTRONS,
SO, WE WOULD HAVE 30 NEUTRONS,
AND THAT WOULD BE CHROMIUM-54.
SO, THAT WOULD BE THE ANSWER TO THE LAST QUESTION.
AND THEN LAST BUT NOT LEAST,
LET'S SEE HOW ALL OF THESE INFORMATION IS SHARED
IN THE PERIODIC TABLE.
NOW, THERE'S NOT ENOUGH SPACE TO SHOW ALL OF THE ISOTOPES
WITH THEIR RELATIVE ABUNDANCES.
SO, WHAT HAPPENS IS ON THE BOTTOM,
THIS IS WHERE WE SHOW THE AVERAGE ATOMIC MASS.
SO, REMEMBERING THAT THIS MASS HAD--
IS A CALCULATION THAT INVOLVES THE VARIOUS ABUNDANCES
WITH THE VARIOUS MASSES OF THE ISOTOPES.
AND WE DON'T HAVE TO WORRY ABOUT HOW THIS IS CALCULATED
BUT WE CAN SEE THAT--
NOTICE THAT THE AVERAGE MASS IS VERY CLOSE TO 52,
WHICH MAKES PERFECT SENSE
BECAUSE CHROMIUM-51 IS THE MAJOR ISOTOPE OF CHROMIUM.
THEN, OF COURSE, WE HAVE THE SYMBOL
AND THEN LAST BUT NOT LEAST,
WE HAVE THE ATOMIC NUMBER Z. AND MANY PEOPLE,
WHEN WE FIRST ENCOUNTER THE PERIODIC TABLE,
WE CAN FIND THIS VERY IRRITATING
THAT THE ATOMIC NUMBER IS AT THE TOP
OF THE SQUARE FOR EACH ELEMENT.
HOWEVER, WHEN WE WRITE THE SYMBOL,
WE WOULD WRITE THE ATOMIC NUMBER IN THE BOTTOM LEFT CORNER.
SO, THAT IS THE OVERVIEW
OF ATOMIC STRUCTURE FOCUSING ON THE NUCLEUS.
AND AT THIS POINT, IT WOULD BE A GREAT IDEA
TO SPEND SOME TIME PRACTICING A FEW PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.