Transcript MOLE
NOTATIONS TO WRITE ISOTOPES THE NOTATIONS TO WRITE ISOTOPES ARE A X Z AND X-A EXAMPLE: Ne HAS THREE STABLE ISOTOPES Ne-20, Ne-21, and Ne-22 IONS • IONS ARE FORMED BY LOSING OR GAINING OF ELECTRONS • DURING CHEMICAL CHANGE, ATOMS CAN LOSE OR GAIN ELECTRONS TO FORM IONS • IONS CAN BE POSITIVELY OR NEGATIVELY CHARGED • EXAMPLE: Li FORMS POSITIVE IONS( Li+)BY LOSING AN ELECTRON • F FORMS NEGATIVE IONS (F-) BY GAINING ELECTRON IONS AND THE PERIODIC TABLE • A MAIN GROUP METAL TENDS TO LOSE ELECTRONS AND FORMS A CATION WITH THE SAME NUMBER OF ELECTRONS AS THE NEAREST NOBLE GAS • AMAIN GROUP NON METAL TENDS TO GAIN ELECTRONS AND FORMS AN ANION WITH THE SAME NUMBER OF ELECTRONS AS THE NEAREST NOBLE GAS • EXAMPLE: Li LOSES AN ELECTRON AND FORM A 1+ CATION WHICH HAS THE SAME NUMBER OF ELECTRONS(2) AS He • Cl, A NON METAL (17e-)TENDS TO GAIN ELECTRON AND FORMS AN ANION WITH THE SAME NUMBER OF ELECTRONS AS Ar(18e-) MASS SPECTROSCOPY • MASS SPECTROMETRY – USED TO MEASURE THE MASS AND THE RELATIVE ABUNDANCE OF ISOTOPES OF ELEMENTS • ITS A TECHNIQUE THAT SEPERATES THE PARTICLES ACCORDING TO ITS MASS MASS SPECTROSCOPY • -ATOMS WHOSE MASS TO BE MEASURED ARE FIRST INJECTED AND VAPORISED • -AN ELECTRON BEAM COLLIDE WITH THE ATOMS AND IONISES THE ATOMS • -IONS ARE THEN ACCELERATED TO A MAGNETIC FIELD • - THE IONS DRIFT THROUGH THE MAGNETIC FIELD AND EXPERIENCE A FORCE THAT BENDS THEIR TRAGECTORY MASS SPECTROMETRY • -THE AMOUNT OF BENDING DEPENDING ON THE MASS OF IONS • -THE TRAGECTORIES OF THE LIGHTER IONS ARE DIFFLECTED MORE • -FINALLY THE IONS OF DIFEERENT MASSES STRIKE THE DETECTOR AND PRODUCE ELECTRICAL SIGNAL WHICH IS RECORDED • -THE SEPERATION OF IONS PRODUCES A MASS SPECTRUM • - MASS SPECTRUM IS USED TO ANALYSETHE ATOMIC MASS OF THAT ELEMENT MASS SPECTROSCOPY • -MASS SPECTROSCOPY CAN BE USED TO ANALYSE AN UNKNOWN MOLECULE AND TO DETERMINE HOW MUCH OF IT IS PRESENT IN A GIVEN SAMPLE • - DURING IONISATION, THERE WILL BE LARGE NUMBER OF PEAKS FROM DIFFERENT PARTS OF MOLECULE • - THERE WILL BE PEAKS REPRESENTING THE MASS OF THE MOLECULE AS A WHOLE • MASS SPECTROSCOPY IS THE FINGER PRINT OF A MOLECULE • APPLICATION – SINCE 1990, MASS SPECTROSCOPY HAS BEEN USED TO ANALYSE BIOLOGICAL SAMPLES TO ANALYSE THE PRESENCE OF CANCER MOLAR MASS • COUNTING ATOMS IN A GIVEN SAMPLE IS DIFFICULT • THE CHEMISTS ALWAYS WANT TO KNOW THE NUMBER OF PARTICLES IN A GIVEN MASS TO PREDICT A CHEMICAL REACTION • WE CANNOT COUNT THE ATOMS BY ORDINERY MEANS • WE COUNT THEM BY WEIGHING • WHEN COUNTING LARGE NUMBER OF OBJECTS WE OFTEN USE UNITS SUCH AS A DOZEN • THE CHEMISTS' " DOZEN" IS THE MOLE • A MOLE IS THE AMOUNT OF MATERIAL CONTAINING 6.02× 1023 PARTICLES AVAGADRO NUMBER • MOLE – AMOUNT OF SUBSTANCE • NUMBER OF MOLES OF A SUBSTANCE = AMOUNT OF THE SUBSTANCE • THE VALUE OF THE MOLE IS EXACTLY EQUAL TO THE NUMBER OF ATOMS IN EXACTLY 12G OF C-12 • 12g OF CARBON = 1 MOLE OF CARBON = 6.02× 1023 NUMBER OF CARBON ATOMS • AVOGADRO NUMBER IS 6.02× 1023 PARTICLES MOLAR MASS • MOLAR MASS OF A SUBSTANCE IS THE MASS OF 1 MOLE OF THAT SUBSTANCE • AN ELEMENT’S MOLAR MASS IN GRAMS PER MOLE IS NUMERICALLY EQUAL TO THE ELEMENT’S ATOMIC MASS IN ATOMIC MASS UNIT • 26.98 G OF Al = 1 MOLE OF Al = 6.022×1023 Al ATOMS • 12G OF C = 1 MOLE OF C = 6.022×1023 C ATOMS • THE LIGHTER THE ATOM, LESS MASS IN 1 MOLE OF ATOM 1.CALCULATE THE NUMBER OF Cu ATOMS IN 2.45 MOLE OF Cu 22 10 2.A PURE SILVER RING CONTAINS 2.80× SILVER ATOMS. HOW MANY MOLES DOES IT CONTAINS? CALCULATE THE AMOUNT OF CARBON IN MOLES CONTAINED IN 0.0265g PENCIL "LEAD" (ASSUME THAT PENCIL LEAD IS MADE OF PURE CARBON) HOW MANY COPPER ATOMS ARE THERE IN A COPPER PENNY WITH A MASS OF 3.10g(ASSUME THAT THE PENNY IS COMPOSED OF PURE Cu) Silver( Atomic Weight 107.868) has two naturally-occurring isotopes with weights of 106.91 and 108.90. What is the percentage abundance of the lighter isotope?