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Download A or `Mass Number` - Uplift Pinnacle Prep
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WHAT DO THESE BOXES MEAN?? Number of protons/ Atomic Number All atoms of the same element have the same number of protons THE ATOM…THROUGH THE YEARS THE ATOM…THROUGH THE YEARS IF WE MADE A SCALE MODEL OF AN ATOM AND WANTED TO USE COWBOY STADIUM AS OUR ELECTRON CLOUD, THE NUCLEUS OF THE ATOM WOULD BE THE SIZE OF THE ERASER ON THE END OF YOUR PENCIL. AN ELECTRON WOULD STILL BE SMALLER THAN THE POINT ON A STRAIGHT PIN. AVERAGE MASS OF SUBATOMIC PARTICLES Subatomic Electric Particle Charge Electron -1 Mass Number (amu) 0 Atomic Mass Unit Proton +1 -24 1 amu = 1.66 x 10 g Neutron 0 Location 1 Electron cloud Nucleus 1 Nucleus Isotopes ATOMS OF THE SAME ELEMENT WITH DIFFERENT NUMBERS OF NEUTRONS (THEREFORE HAVE DIFFERENT MASSES). TWO ISOTOPES OF SODIUM ISOTOPE SYMBOL X: element symbol ISOTOPE SYMBOL A: Mass Number #protons + # neutrons in the nucleus Always larger than Z ISOTOPE SYMBOL Z: Atomic number #protons ISOTOPES OF SODIUM 23 11 Na 24 11 Na 2 WAYS TO WRITE ISOTOPE SYMBOL 23 11 Na Or Sodium-23 EXAMPLE PROBLEM • Write the isotope symbol for the chemical element that has 6 protons and 8 neutrons WORK IT OUT! • Take out Whiteboards and Markers • Talk over answer with partner • Raise board when directed #1 • Write the isotope symbol for the chemical element that has 17 protons and 16 neutrons 33 17 Cl or Chlorine-33 #2 How many protons are in the isotope 54Cr? (Chromium-54) 24 (like every atom of Chromium) #3 How many neutrons are in the isotope 42Ca? 22 neutrons #4 How many electrons are in the isotope 23Na? 11 electrons QUICK BREAK … BY THE END OF THE CLASS TODAY I WILL BE ABLE TO… •calculate the average atomic mass of an element using isotopic composition AVERAGE ATOMIC MASS •the weighted average of the atomic masses of all naturally occurring isotopes of an element. Where can we find the average atomic mass of each element? WHAT IS THE DIFFERENCE?? • The A or ‘Mass Number’ is the mass of that specific isotope • The number on the periodic table is the average of all the existing isotopes • Example of Carbon LET’S TAKE A LOOK AT PENNIES… The US mint estimates that of all the pennies currently in circulation 66.5% of them are “new” (post-1982) pennies and 33.5% are ‘old’ pennies. A ‘new’ penny weighs 2.5g and an old penny weighs 3.1 g. Use this information to determine the average mass of a penny. HOW DO WE CALCULATE THE AVG. MASS OF A PENNY? Penny Year Mass (grams) Percentage in Circulation Post-1982 2.5g 66.5% Pre-1982 3.1g 33.5% 2.5 + 3.1 = 5.6 5.6 ÷ 2 = 2.8 grams WE MUST TAKE INTO CONSIDERATION THE PERCENTAGES OF EACH TYPE OF PENNY! Penny Year Mass (grams) Percentage in Circulation Post-1982 2.5g 66.5% Pre-1982 3.1g 33.5% (2.5 x 0.665) + (3.1 x 0.335) = 2.7 grams WHAT IS THE AVERAGE ATOMIC MASS OF COPPER?? Isotope Copper-63 Copper-65 Mass Number 63 65 Percentage Natural Abundance 69.17% 30.83% (63 x 0.6917) + (65 x 0.3083) = 63.61 grams YOU TRY: Rubidium has two common isotopes, Rubidium-85 and Rubidium-87. If the abundance of Rubidium-85 is 72.2% and the abundance of Rubidium-87 is 27.8%, what is the average atomic mass of rubidium? QUIZ TIME