hello and welcome to earth science lecture two atoms and chemical bonds when minerals are carefully examined even under optical microscopes the innumerable tiny particles of their internal structures are not visible nevertheless scientists have discovered that all matter including minerals is composed of minuttes building blocks called atoms so before we discuss these minerals and rocks in our upcoming lectures we begin with a discussion of atoms and their chemical bonds quick notes if you're in my actual class the textbook doesn't cover this too much and I think it's actually a little important to go over this so this is a supplemental lecture basically to what you might see in your textbook alright so Greek philosopher Democritus who lived from 462 362 BC developed an atomic model which states that the universe and all matter obey the following principles first everything is composed of atoms which are physically indivisible - between atoms there lies empty space or what was called a void three atoms are indestructible note that atom of is a greek term for uncuttable so you can see where that comes from atoms have always been and always will be in motion and the last one there is an infinite number of atoms and an infinite and kind number of kinds of atoms which differ both in shape and size so at the time neither plato nor aristotle accepted the atomic theory of matter and it was not until about 2,000 years later that this atomic concept of matter was reintroduced so in comes dalton in the early 1800s so again we're talking almost 2,000 years later English chemist English chemist John Dalton brought back the idea of indivisible atoms to explain chemical reactions five statements summarize his theory so we're gonna go through five again indivisible my newts particles called atoms make up all matter so he we are at the idea of atoms once more all of these atoms of an element any particular elements are exactly alike both in shape and mass notes that this is not necessarily true today as we now know of the existence of isotopes which are atoms with different masses we'll talk about that soon next the atoms of different elements differ from one another in their masses atoms chemically combined indefinite whole number ratios to form chemical compounds and last but not least atoms are neither created nor destroyed in chemical reactions so there's some conservation there so acceptance of this didn't come easily there was still resistance full acceptance of the atom came in the early 1900s with the discovery of the atom well which was not indivisible after all so I'm going to take you through a brief history of basically the study of atoms in the late 19th century scientists were interested in studying the nature of electric current and began to experiment with cathode ray tubes these are sealed glass tubes from which most of the air has been evacuated a high voltage is then applied across two electrodes basically just two metal plates so you can see that in the image here there's a cathode and an anode on opposite sides so a high voltage was applied across them inside of this tube and caused a beam of particles to flow from the cathode the negative side to the anode the positive side so you run a current through it and suddenly you see a beam well here's where it gets really interesting and admittedly in depth so just to be clear there's gonna be some numbers thrown in here you don't need to know these if you're in my class I just include them for just general information an 1897 English physicist Thompson JJ Thompson that is placed two oppositely charged electric plates around the cathode ray the Ray was deflected away from the negative plates thus the cathode ray must have been composed of negatively charged particles because as we might have might have heard before like charges repel one another so if there is a beam passing through this electrode and there being reflected away from the negatives that must mean the particles themselves must be negative so the cathode ray was also deflected when passed between the poles of a magnet we were able to balance the deflections made by the magnet with an electric field and we were able to find that the charge to mass ratio of these particles was the number given roughly 1.75 times 10 to the 11th coulombs per kilogram now again that's a number that might not make a lot of sense but you'll see why it becomes important very soon so we know not the charge of these particles on their own and not their mass on their own but we know the ratio of the two anyway this will come back on the next slide the discovery of I'm sorry eventually these cathode ray particles were given the familiar name of electrons fundamental particles the discovery of the electron disproved the part of Dalton's theory that assumed that atoms were indivisible because we saw particles that were smaller in order to account for the existence of electrons an entirely new atomic model was needed so at this point I would recommend pausing the video and going to the following link or the link that you can find in the YouTube description to see I think a one-minute video of one of these cathode ray tubes actually being used it's quite fascinating and you can see how a magnet actually defect deflects the beam continuing on in 1906 Milliken measured the charge of an electron by balancing the pull of gravity on oil droplets with an upward electric force so this is actually an experiment that I did would and I was in my undergraduate studies we basically have a chamber inside of it there's two plates that are connected to a battery so this symbol here means battery so there's charge running into this you can see this plate at the top is positively charged this one at the bottom is negatively charged and if you adjust this the current running into these basically you'll balance the electric field created between the two with the weight of these little particles on their own so electric is electric forces pointing upward gravity is pointing down eventually they balance well this is extremely important he found that all of the oil droplets had a charge of 1 point 6 times 10 to the minus 19 coulombs or a multiple of that number this must have been the charge of these electrons so with this experiment we finally found the charge of an electron knowing both the charge of a single electron and that charge to mass ratio we discussed on the previous slide we could then calculate the mass of an electron by simply dividing the two numbers we found that the mass of an electron was about 9 point 11 times 10 to the minus 31 kilograms that's about one one thousand eight hundred and fortieth the mass of a hydrogen atom so again the numbers themselves don't matter too much but I just like to include these just for the sake of being an interesting fact and it brings us to our concluding discussions later on and notes I keep saying we did this I don't know why I'm including myself but I guess I'm using myself as a scientist in a sense so now we are developing a new model for the atom atoms themselves are electrically neutral which means it's not positive or negative so if there is an electron inside of an atom well then there must be something else that's positively charged to cancel out that negative charge right so their overall neck but because there's negatives inside there must be positives as well so this brings us to the new idea that Thompson came up with so this led Thompson to propose that atoms could be described as net negative particles floating within a soup of diffuse positive charge this model was often called the plum pudding model of the atom due to the fact that apparently it's description is very similar to the plum pudding which was a popular English dessert I guess it doesn't look very good to me but I guess looks can be deceiving but here's basically the plum pudding and here's just a representation of this plum pudding model and have we know this is not true today but it's not a horrible guess at the time well we continue on all matter is composed of atoms the smallest particles that constitute elements and cannot be split by chemical means in 1907 physicist Ernest Rutherford was studying the scattering of radiation particles directed toward a thin sheet of gold which can see in the image on the right most of the particles passed through the gold sheets but some were deflected at random varied angles so what he stated as a result was that particles were being repelled by a massive positive charge concentrated in a very small region of the atom and concluded that atoms must have a tiny positively charged nucleus surrounded by negatively charged electrons so this is getting much closer to our modern understanding of atoms both protons which are the positive charges inside of atoms and electrons share a fundamental property called electric charge so protons have a charge of positive one electrons have a charge of negative one neutrons as the name suggests have no charge the charges of protons and electrons are equal but opposite and so these two particles are paired and the charges cancel out since matter typically contains equal numbers of positively charged protons and even negatively charged electrons most substances are electrically neutral so electrons are moving at a distance of about a hundred thousand times the radius of the nucleus thus the volume of an atom is mostly empty space a few years later Rutherford was able to identify the discrete unit of positive charge again that we now know as a proton he also speculated about these existence of this neutral particle that we call the nuke the neutron the neutron was eventually identified in 1932 by James Chadwick protons and neutrons are very dense particles with almost identical masses by contrast electrons have a negative negligible maths that's about 1 mm that of a proton to visualize this difference imagine a scale on which a proton or neutron has the mass of a baseball an electron will have a mass of a single grain of rice as a comparison so now we're moving to the more modern theory so if you look at this image on the right we discussed Dalton at the beginning Thompson's plum pudding model and then this Rutherford model we didn't really give the name bore but Bohr basically said that there's a solar system model and that these electrons are orbiting around the central nucleus so illustrations sometimes show this that electrons orbit the nucleus in a manner that resembles planets of our solar system orbiting the Sun however electrons do not actually behave this way a more realistic depiction which show electrons as a cloud of negative charges surrounding the nucleus studies of the arrangements of electrons show that they move about the nucleus in a region called principal shells or what we call orbitals each with an Associated energy you might have heard of this but the Heisenberg uncertainty principle basically states that you cannot measure the exact position of an electron the location of the electron can only be described in terms of probabilities of where it might be at some instant the probability of the location is described by this fuzzy 3d region you see in the image on the right again that we call an orbital so we don't know exactly where it is but we know it must be somewhere perhaps in a certain region each of these orbitals can hold only a specific number of electrons with the outermost shell or orbital containing valence electrons these electrons are those that can be transferred to or shared with other atoms to form chemical bonds so there might be a electrons in multiple levels or multiple orbitals but it's only those in the very outside that end up being shared or lost to other atoms to create these bonds so it is the number of electrons in the outermost orbital the valence electrons that usually determines the chemical properties of an atom atoms have a tendency to seek a stable filled outer orbital this tendency is what we call the octet rule atoms attempt to acquire an orbital with eight electrons in their outer shell so the simplest atoms have only one proton in their nuclei whereas others could have over 100 the number of protons in the nucleus of an atom called the atomic number determines the add atoms chemical nature all atoms with the same number of these protons have the same chemical and physical properties collectively they constitute what we call an element there are about 90 naturally occurring elements and several more that have been synthesized in laboratories and we'll take a look at the periodic table in just a moment but you can find all of them on the periodic table although the although all the atoms in an element must have the same number of protons in the nuclei the number of neutrons can actually vary atoms of an element that have different numbers of neutrons are called isotopes the sum of the number of protons and neutrons is what we call the mass number of an atom mass numbers are used to identify isotopes so we're starting to get into some really detailed discussions here this goes well into chemistry and we could go on for this discussion for a very long time but the main idea is that here we have an example of say hydrogen hydrogen's the first element on our periodic table it consists of one proton and one electron well there are other forms of hydrogen notes if you look at this there's hydrogen what we could call hydrogen - when hydrogen 3 we give them names deuterium and try T reom note that they all have a single proton and electron so they're all still forms of hydrogen they have one p and one e but they have different numbers of neutrons so these are isotopes of hydrogen hydrogen can come in several forms and this happens for other elements as well not just hydrogen so now we bring up the discussion of the periodic table so this is going to be a little bit annoying for a second here because I'm gonna be flipping back and forth between this slide and a picture of the periodic table I think it will help even though it's gonna be annoying going back and forth so the periodic table which I'll skip this real quick and show you the periodic table is made up of rows and columns of cells the arrangement has a very serious very against I'll say serious meaning both about atomic structure and chemical behaviors so these cells of the periodic table so each little square and give the element as identified in each cell with a chemical symbol the number above the symbol is the atomic number and the number below is the atomic mass so we discussed a topic number previously but we won't go into atomic mass too much and that's just basically the mass of the element plus its isotopes that are found in nature varied by their concentrations but that's beyond our scope for this course so each cell here shows the atomic number the symbol so be the atomic mass below and then the name so B is for boron for example well notice there's rows and columns as well the rows are also called periods these horizontal rows of elements run from left to right an increase in atomic numbers these periods or rows are numbered from 1 to 7 so you'll notice again that there are 7 rows in the periodic table from 1 2 3 4 5 6 and 7 at the bottom well the columns are also organized in a familiar way we call these families or groups elements in the same family have similar chemical properties in other words they have the same number of valence electrons those are the electrons and the outermost shell so all of these elements in the first column have one valence electron all of them in the second column have two we skip over the elements in the middle here and over to here so this is the third column you can see by the Roman numeral three these have three valence electrons and so on and so forth so they all have the same chemical properties you'll notice that the tables also subdivided into a and B groups this is a beyond the scope of our course so a bit but just to give you an explanation of why this is members of the a group are called representative elements and those in B are transition elements or metals so if you ever need to reference a periodic table you can of course always look it up on the Internet view your textbook but there's one here if you need it okay so I mentioned that all of the columns are divided by how many valence electrons these elements have in their outer shell well we have a way to represent this each period or Row begins with a single electron in a new orbital that is my dog sneezing by the way I'm sorry for that he is going totally mental anyway each period ends with the filling of an orbital so you start with one so here is a dot representing one electron as you move over increases and increases all the way up to eight in the final column so they always go from one to eight from left to right the number identifying the group per column also identifies these numbers of electrons in the outer orbital the outer or valence electrons are represented with an electron dot notation which you see in this picture made by writing the chemical symbol with dots around it indicating the number of outer orbital electrons so we won't go into this anymore but the idea is they always want eight so they want to get up to these elements on the right that we call noble gases so whenever we see chemical bonds hydrogen might give up its one electron to pair with something that has perhaps seven so together they share their eight but anyway the point is we have these outer electrons called valence electrons they always want to have eight and the way they bond and chemical compounds will be determined by this so speaking of these chemical bonds let's at least just go through the basics so atoms have a tendency to seek that stable filled outer orbital changement in other words they want eight electrons this tendency is called again the octet rule atoms tend to gain lose or share electrons until they are surrounded by eight valence electrons by chemical reactions such a reaction is what we call a chemical bond these are attractive forces that hold atoms together in a compound so it turns out that there's actually three general classes of chemical bonds we have ionic bonds in which electrons are transferred covalent bonds in which they're shared and metallic bonds in which they're actually able to move freely and this is one of my favorite images the shows in a kind of a cute way each of these bonds so ionic is when they're transferred so here you can see one of the atoms giving his electron to the other and the second one they're shared so you can see them sharing their electrons and it's harder to depict this one but in metallic bonds electrons are free to move around so you can kind of see ones playing baseball with them they're moving all over so let's look at this in a little bit more detail let's start with ionic bonds an ionic bond is defined as the chemical bond of electrostatic attraction between negative and positive ions in other words the negative and positive attract one another ionic bonding occurs when a metal reacts with a nonmetal resulting in the transfer of a valence electron from the metal to the nonmetal the atom that loses the electron becomes a positive ion right so if you lose a negative you're becoming positive and the atom that gains the electron becomes a negative ion opposite charges attract one another so you give up an electron and become positive the other one is acquiring a negative so now they're oppositely charged and as a result they attract to one another and so the result is a crystalline solid that is typical of salts like sodium chloride NaCl which is table salt so to give you an example of this we can take a look at this graphic in the middle when sodium chlorine chloride I'm sorry excuse me when sodium and chlorine collide or mix a valence electron is transferred from the sodium to the chlorines here's the one-electron it gives up its one electron to the chlorine this produces a sodium ion and a chlorine ion the reaction can be shown with these dots the chlorine atom accepted the electron in its outer orbital to acquire a stable electron configuration of eight a stable positive ion and a stable negative ion are now formed due to opposite electrical charges they attract one another and produce this ionic bond so I just love these two little images so here is sodium and chlorine and it says you complete Micah's together they satisfy the octet rule as if that wasn't lame enough already and then the bottom amateur is just a really terrible joke but one of my favorites it says I lost an electron are you positive because again if you give up an electron you become positively charged anyway moving on here we can see this crystalline structure of salts that we mentioned previously so notice that salt consists of alternating sodium and chlorine ions positioned so that each positive ion is attracted to a surround is attracted to and surrounded on all sides by negative ions and vice-versa so this arrangement maximizes the attraction between ions with opposite charges while minimizing the repulsion between ions with identical charges thus ionic compounds consists of an orderly arrangement of oppositely charged ions assembled in a definite ratio that provides overall electrical neutrality so that's a mouthful the idea is opposites attract likes repel so they're going to order themselves in such a way inside of the structure so that the negatives are as far away from one another as possible so we can say these little purple guys and then the green ones are as far away from one another so they alternate positive negative positive negative in the most efficient way possible and the results is a crystalline solid so we get little cubes and that is a magnified image of table salt as an example the second type of bond we looked at is a covalent bond most substances are molecular meaning that they're composed of electrically neutral groups of atoms that are tightly bound together other words they're not ions like we talked about previously a covalent bond is a chemical bond formed by the sharing of at least a pair of electrons so how does this work how do they share them so let's imagine two hydrogen atoms each with a single electron moving toward one another so here on the right we have an image of two hydrogen atoms so there have a positive one charge and notice this is the cloud of probabilities of where the electron could be so they're moving toward one another well as these two atoms move closer together their orbitals will overlap meaning the cloud in which the probability of an electron existing will overlap with the other so each electron is going to be attracted to the opposite Li charged positive nucleus of the other atom so here you have a negative somewhere floating around well it's going to get attracted to the positive of the other one and vice-versa so as a result they're going to move closer and closer together and they overlap will tighten well then the repulsive forces of the two liked charged nuclei the two positives are going to start to slow down this merge eventually they will stop because the two positives will get close enough together where they resist each other enough to stop them from moving any closer and thus we reach a state of stability and an h2 molecule will have been formed hydrogen two so the two electrons are now shared by both of these elves so this is a covalent bond so what determines whether it's going to be ionic or covalent so far we've talked about these two and how do we know the difference in general ionic bonds form between metals and nonmetals while covalent bonds form between two nonmetals if an atom has a much greater electron pulling ability than the other well then the electron is pulled completely away then the up from the other leaving an ionic bond but if the election on pulling ability is kind of even between the two atoms well then they're gonna just end up sharing it because they can't pull it away from the other one so it has to do with the electron pulling ability of the two atoms involved so if you can pull really strong and take that electron away you get non ionic bond but if they can't really pull too hard you get covalent the last type of bonding that we looked at is a metallic bond a few minerals such as native gold silver and copper are made entirely of metal atoms packed tightly together in an orderly way the bonding that holds these atoms together results from each atom contributing its valence electrons to a common pool of electrons with freely moving parts throughout the entire metallic structure so that's what you're seeing here on the writes in this new figure so here is the orderly packing of metal atoms and you'll notice these blue arrows and dots are representing electrons freely moving all around the contribution of one or more valence electron leaves an array of positive ions immersed in a sea of these valence electrons metals are good conductors of electricity because the valence electrons are free to move from one atom to another metals are also malleable which means that they can be hammered into thin sheets and they're ductile which means they can be drawn into thin wires so this is very important the reason why our metals are good conductors of electricity is because these electrons can just flow through them by contrast ionic and covalent solids tend to be brittle and fracture when stresses are applied consider the difference between dropping a metal frying pan and ceramic plates unto the floor so before we go to our questions that is one thrown one slide the study of chemistry is actually very important and even a basic understanding is important for us in the real world so here's an example of something really important this is titled why we need to ban D h mo D HMO or dihydrogen monoxide is a colorless odorless and tasteless substance and it kills uncounted thousands of people every year most of these deaths are caused by accidental inhalation of D H mo but the dangers do not end there prolonged exposure to its solid form causes severe tissue damage symptoms of D H MO and Jeff Chinn can include excessive sweating and urination and possibly a bloated feeling nausea vomiting and body electrolyte imbalance for those who will become dependent on D HMO withdrawals mean certain death well this sounds scary if you don't know a little bit about basic chemistry and we don't go into the naming too much but dihydrogen mono oxide is the same as h2o dye means two hydrogen's so two hydrogen's mono means one so one oxygen so that's two hydrogen's one oxygen that's h2o so the above is a part of a hoax that was recently circulated on the Internet I say recently I think it started years ago but still the truth is that this is just the name of water but all of that can be said accurately about water and so you have to be careful right it's good to have basic understandings of scientific terms even if you don't go into Sciences for a career so at this point let us get into our questions for this lecture question number one what determines the physical and chemical properties of an atom remember at this point we pause the video so you can come up with your answer and whenever you're ready continue well the answer is C it's the number of protons in the atom so remember the number of protons is very important if we have one proton its hydrogen two is helium and so on and so forth question number two electrons have a blank charge and a mass that is blank than that of protons well hopefully you answered d electrons have a negative charge and a mass that is smaller than that of protons so electrons are those negatively charged particles that exist in those orbitals around our positively charged nuclei and they have very low masses about mm to that of a proton question three atomic bonding which involves two atoms sharing one or more electrons is known that what is what of bonding if any all right so remember when we share electrons we are talking about covalent bonding covalent bonds involved the sharing of one or more valence electrons between a pair of atoms okay last question for this lecture number four when an atom loses an electron it becomes what the answer is be a positively charged ion if an atom loses an electron it is left with a net positive charge so note you might have answered proton but it doesn't turn into something entirely different right it just becomes positively charged alright so I know this is a very involved lecture and this is the probably the most involved one will have for quite a while at least in terms of the scientific background but again I feel that this was very important to our discussion when we get into minerals and rocks simply because they involve all of these kinds of bonds so take this as you will you don't have to know all chemistry and it's not super important but I think we needed to cover it and I hope you at least learn something through this lecture and as always thanks for watching and have a great day