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Science-10 E.Brennan Atomic Structure is a counting number equals the number of protons is the identity of the element (all atoms of a given element have the same # of protons) is a counting number equals sum of protons + neutrons (is not equal to 2 x protons since protons and neutrons do not always come in identical numbers) is a calculated (think ‘decimal points’) number approximately equal to sum of protons + neutrons (which make up essentially the mass) 1. Within atoms of the same element, the number of ________________will never vary from one atom to the next. 2. Within atoms of the same element, the number of ________________will vary from one atom to the next. These various form of the element are called ___________________. 3. All the isotopes of a particular element have the same ___________________ but they have different _____________________________. 4. ______ elements exist naturally as a mix of isotopes, so the________ number we use is just a way of indicating which isotope we mean. 5. The _______________________ is actually a weighted average of all naturally occurring isotopes (taking into account how frequently each is found). 6. In a neutral atom the number of ____________ equals the number of ___________. 7. If the atom is charged it is because it gained or lost one or more ________________. Example: charge of 2+ is the result of ________________________, while charge of 3- is the result of ______________________. 8. Charged atoms have mass that is _________________________ than their neutral counterparts. Science-10 E.Brennan All atoms in chart are neutral. Symbol 1 Name Atomic Number Atomic Mass Neutrons B 2 11 4 Isotopic Symbol 39 88.9 39 29 35 Pb 208 7 103 8 9 Mass Number 23 31 5 Electrons 6 3 6 Protons 70 89 Mo 54 10 12 6 C 11 14 6 C 12 10 5 B So, what’s up with all these isotopes anyway? In nature elements are not made up of atoms that are all exactly the same! Some will be heavier than others, even though they are still the same type of atom. C-12 and C-14 are both Carbon, with all the usual Carbon properties, but the C-14 has two more neutrons, and is heavier. Both Carbons exist in nature, but in different abundances. They are not 50/50 or else we would average the two weights and report a calculated Atomic Mass in the periodic table of 13. Because the reported Atomic Mass is very very close to 12, we know that almost all of the Carbon found in nature is C-12, with a teeny bit of C-14. Look up Chlorine in the periodic table. In nature it consists of Cl-35 and Cl-37. Since its Atomic Mass is reported to be 35.45 we can conclude which isotope occurs the most (...........right?) (You will look at the math behind these calculations in Chem11.)