all right this this lecture is a brief introduction to atomic theory and uh basically what you see in front of you is the periodic chart and there are of the elements that occur remember what an element you know all elements have unique atomic numbers and unique properties that defines them at the atomic level um used to be thought there was 92 uh the only of the elements that exist 92 occur nationally on earth that number because of some trace element discoveries is now more like 96 or 98 but there's almost 120 elements the higher atomic number ones of course were made artificially in the laboratory and exist for very brief amounts of time so the atom is the smallest part of an element that can retain the properties of the element and enter into chemical combination major atomic particles are the protons that have a positive charge and mass of one atomic mass unit or one-twelfth mass of a carbon nucleus atom nucleus a neutron has no charge and the mass of one amu we also say we can measure these very precisely so actually the mass of neutron is slightly greater than that of a proton electrons have very small mass but for bookkeeping purposes we say no mass but that's not exactly true and a negative charge there's many protons surrounding as many electrons surrounding the nucleus of a neutral atom as there are protons within the nucleus we won't get into subatomic particles at this point it's not necessary but quarks are subatomic particles that comprise protons and neutrons uh neutrinos and neutral subatomic particles of very small mass atomic number again defines the elements the number of protons in the nucleus of an atom atomic mass is the total number of protons and neutrons in the nucleus of an atom an atomic weight is the average of the atomic masses of the isotopes of an element of the natural you know they're naturally occurring isotopes of an element isotopes are atoms of an element that have different masses different numbers of neutrons in their nucleus they have to have the same number of protons or it's a different element okay so again there are about 1700 known isotopes but only 264 are stable stable isotopes uh that we have on earth were primarily formed at the time of the formation of you know incorporated time of the formation of the planet and the radiogenic isotopes you know some of them have very long half-life some of them are very short half-lives so the ones that ultra long half-life still exists on earth in the short half-lives only ones only exist because we make them in the laboratory or they're the residual products of say a nuclear bomb we'll talk about holy you know bonding is necessary and and you know again with different you know bonding is the sharing exchange of electrons between atoms of elements to form compounds this is how minerals form uh this is how water forms you know again covalent bonding or sharing of electrons between hydrogen and oxygen to fill their outer shells of electrons consumed to achieve a stable state ionic bonding is the exchange of electrons between atoms to achieve a stable state where you end up with ions sodium and chloride ion again are the major ions in seawater chloride being the most abundant sodium in the second most divine and many compounds form we'll see by combination of ionic and covalent bonds for calcite for example which is a you know a major mineral component of limestone marble uh it's a major you know component of the shells of organisms many shows organisms make the shells out of calcium carbonate and carbon oxygen bonds are covalent and the calcium and carbonate bonds that hold them in the mineral together are ionic so let's just take a quick look a couple hydrogen is the most abundant element in the universe all elements form by nuclear synthesis from hydrogen you know as stars form and go through their cycle and reach high high temperatures and we have nuclear nuclear reactions that lead to the formation of other elements from it second most abundant element in the universe is helium okay hydrogen again has an atomic number of one so it has one proton in its nucleus okay but you'll notice the atomic weight of hydrogen is 1.008 what does that mean this is what it means you can read this there are two naturally occurring stabilized in terms of hydrogen while 99 of the hydrogen on earth is hydrogen one a small percentage is another stable isotope hydrogen two uh and hydrogen two has one proton and one neutron in its nucleus it was discovered a long time ago and in early about 1931 my advisor's advisor proved the existence of this isotope of hydrogen received the nobel prize for doing that and we name this this isotope deuterium okay to stabilize the type of hydrogen so those two isotopes the abundances on earth were set at the time of the earth's formation however there are as we'll see in the course of the semester there are processes that cause the redistribution of these isotopes simple ones sometimes physical sometimes biological a simple one would be evaporation molecules that contain the lighter isotope water molecules that contain the lighter isotope of hydrogen well because of the difference in vapor pressure will more easily evaporate than water molecules that contains a heavy isotope of hydrogen there's not much of it as we call that we'll see a fractionation there's a third isotope of hydrogen that you may be familiar with that has a a mass of three atomic mass of three which means it has one proton its nucleus and two neutrons okay it has a very it's an unstable isotope however hydrogen it has only half a short half-life of 12 years or so and so there is no tritium on earth from the time of the earth's formation the only reason we have it on earth is from nuclear explosions it forms as a as a product of byproduct of a nuclear reaction like that an explosion and so that's why we still have some tritium on earth it's kind of ironic because we'll see that tritium you know comes from nuclear testing and yet when it combines with oxygen in the atmosphere and then enters the hydrologic cycle it's a very useful probe for following water going through this going through the hydrologic cycle so environmentalists love it and yet the way it forms is by nuclear bombs matter of fact some of the residual products of of nuclear bomb testing enables scientists to know when a country has really detonated a nuclear device or not by by monitoring the fallout in the atmosphere so because there's a small amount of naturally occurring deuterium on earth the atomic number of hydrogen i mean the atomic weight of hydrogen being the average of the isotopes is slightly greater than one similarly carbon exists as two stable isotopes carbon 12 and 13. they both have atomic number six or 99 of the carbon on earth is carbon 12 and about 1 is 13 and again there are product processes that occur that cause the redistribution of these isotopes in nature and that's what i study i'm an isotope i study you know these processes and that's you know and how they read how physical and biological processes cause redistribution of these isotopes in nature and how we use those as probes for studying everything from changes in ocean water chemistry to trophic levels in ecosystems to establishing diets of ancient organisms things like that i'll show you later i'll put them up online i recently published a paper with colleagues you know using these to trace diets of dinosaurs and i've done a lot of work on mummies but we'll get to that later okay nitrogen similarly has two stable isotopes nitrogen 14 and 15. usually the light isotope is the more abundant they both have atomic number seven and again they get redistributed by processes that occur in nature that become powerful tools for us to study geological and biological and other oceanographic processes in terms of how they're redistributed oxygen is really interesting i you know oxygen has an atomic number of eight which means there's eight protons in its nucleus there's eight electrons surrounding the nucleus of a neutral atom of oxygen i haven't gotten into the levels of you know the you know how again the way you may remember from chemistry that the electrons occur in discrete energy levels so oxygen has you know two electrons the first energy level has two the next one holds eight so it has six in that it needs two more and it can share with two hydrogens to form h2o all right i'm getting ahead of myself but anyway if you look at oxygen you'll see it's very interesting because oxygen consists of three stable isotopes oxygen 16 17 and 18. okay and remember the oxygen 16 is the most abundant however you know as i mentioned before the atomic weight is the average of the abundances of the naturally occurring isotopes of an element so you might look at this and say wait a minute but how if the lightest isotope of oxygen has a mass of 16 how is the atomic weight 15.9994 i stupidly asked the chemistry teacher that question when i was in high school and he had no answer and told me i was being belligerent threw me out and they suspended me it was a funny story you know so it turns out you know i was lucky a couple of weeks later that because they had to replace the physics teacher they hired this guy dr patelino just come from princeton and i guess they got to talking about this and i was a quiet person back then you know about this and he explained to this chemistry teacher that um you know there's a really good explanation for this but of course back then there was no internet or any way to really look it up and you know so he just didn't want to answer my question because he didn't know how so i'll show you the answer okay again here is oxygen 99.763 percent of 16. a little bit of 17 and a little bit of 18. usually the even ones are more abundant it has to do with stacking the nucleus again beyond our need to discuss here but again i show you in atomic mass units but the actual you know even though for bookkeeping we say a proton as a has a you know is is one you know we say it's one mass unit and a neutron is one but you can see in in actuality they are not uh proton is slightly you know have slightly greater than one and the neutron is slightly greater than a proton in terms of an overall mass so if you do the calculation theoretically simple you know say you have eight protons in oxygen 16 and eight neutrons and you multiply eight times you know the mass of a proton eight times an inch and together you should you would think an electrons being very small mass you would think minimally that the you know the time you know that you know you end up with a you know you know the mass of oxygen 16 should be 16.13 and then 17 and 18 should be a little larger than that so the average of the atomic weight you know you should be 16 point something but you're not you're 15 point nine nine nine four i think now as well i'll get to that minute so what's going on so again if you take oxygen 16 17 18 if you can calculate a theoretical atomic weight of you know given their overall abundances you know times their their masses you get 16.12 9895 but the actual measured atomic weight is 15.9994 the reason for this is was figured out by albert einstein and it was funny because this physics teacher that came to my high school didn't study studied with one of einstein's students and uh that einstein himself and einstein students and they all knew you know basically einstein this is how he came up with you know this is why he used this equation to define e remember e energy equals and mass times the speed of y squared that the sum you know this difference between the actual and the theoretical atomic weight is einstein's mass defect that sum of the mass of the atom is converted to binding energy that holds the atom together so that no none of the theoretical calculations are uh are you know they're basically well they're all off because you have to subtract away you know the amount of of male you have to convert the amount of mass to energy that holds the iron together it just so happens you see it really well with oxygen because you know it's you know with hydrogen okay it's slightly greater than one or carbon is slightly you know greater than 12 but okay and you're sitting there as a kid you say okay it's slightly greater so what you know that makes sense you know but oxygen sort of slams you in the face it says wait a minute how can it be less than 16. the funny thing is at the atomic nuclear energy facility for uh meetings in vienna where we calibrate all of our standards uh it's now been recalibrated to be 15.9998 so pretty soon i'm gonna be out of luck but but it's still less than 16 so it still makes for a good story and they've reluctantly put me back into high school and i uh vowed never to become a scientist see what happens when you you know that's what my sister says people make plans and god laughs anyway onward so you know i have a sort of a question kind of a question thing a question here i put up here just for the first exam you know that i might have a question again just keeping in mind the very general terms you know that that well the uh that you know the the atom of any element you know is going to be the atomic number is going to be the number of protons that defines that element and the atomic mass is the total number of protons and neutrons in the nucleus of the atom and that there are isotopes of these atoms and sometimes there are many okay there are five stable isotopes of calcium as i show in this example and so you know the first question is how many protons are the nucleus of an atom of calcium that has a mass of 46. well if you know as i said above you know the atomic number is 20 so any isotope of calcium has to have an atomic number of 20 or 20 protons if it's not 20 it's not calcium so pretty common sense here you know things like that how many neutrons are the nucleus of an atom of calcium that has a mass of 42 well it's going to be 42 minus 20. so this would be 22. and so on and so forth and and so i'll go over this again you know when we get ready for an exam but i thought i'd just put this in as a kind of a brief introduction for now to my crazy world of isotopes have a great day you