all right so this is the honors chemistry section 4.2 lesson video and so we're going to dive a little deeper into the parts of the atom and kind of how what an atom looks like was actually discovered since we couldn't see one we kind of had to do experiments and things like that to determine what an atom actually looks like so three kinds of subatomic particles are electrons protons and neutrons so hopefully you're familiar with all of those before you step foot in my class particles with the same charge repel one another so like two positives would repel two negatives would repel whereas particles with opposite charges attract one another so like a proton and an electron because one's positive and one's negative they would attract one another so these are just some things you need to know about protons electrons and neutrons so first is the symbol the electron is just e with a negative protons p positive neutron is in with a little zero that's because those are the charges so an electron has a negative one charge a proton has a positive one charge and a neutron has a neutral charge or a zero charge the relative mass is not the actual mass okay the actual mass of protons neutrons and electrons is way less than one but it's saying that if we set a proton at a mass of one that's why we say it's relative if the proton has a mass of one then a neutron also has a mass of about one so in other words what they're saying is a proton and neutron have about the same mass whereas an electron would be one over eighteen forty so in other words an electron is much much lower in mass so that's why when we start talking about mass number for atoms we don't include the electrons they're so small it'd be like if i weighed myself and i stepped off the scale and grabbed a couple of paper clips and then weighed myself again because i have so much more mass than those few paper clips the scale is going to say the same thing okay because it's not going to go out enough decimal places to account for those few paper clips that i might have grabbed so that's why electrons are not included in the mass number so where are they well the electrons are in the electron cloud we'll also call them energy levels orbitals sublevels things like that and the protons and neutrons are both within the nucleus so first let's talk about electrons so in 1897 the english physicist jj thompson discovered the electron electrons are negatively charged subatomic particles the charge of an electron is negative 1.60 times 10 to the negative 19 and c is coulomb that is just a unit for charge and this is called the electronic charge so even though we say it's negative one and a proton is positive one again that's kind of relative the actual coulombic value is this right here so this would be the charge of an electron a proton actually has the same charge but it's positive for simplicity like i said we assign it a charge of negative one whoop that should say up not work thompson discovered electrons by studying a cathode ray tube so a cathode ray tube is a glowing beam that travels from a cathode to an anode it looks kind of similar to like the long fluorescent bulbs up in the lights at school not quite that long though and slightly different okay so it looks something like this so what they did was they kind of put a slit so that the beam could be concentrated more almost like a laser not the same thing but it's a smaller beam and then he put a positive plate and a negative plate on either side because he's trying to figure out what is the cathode ray like what is it made of why is it lighting up when i pass electricity through this um gas so he noticed that when he did that the beam would bend towards the positive plate well what attracts to a positive a negative and so that's when he determines hey there must be some negative particles and that's where we figured out about electrons so i'll see if this video will play it could it could not doesn't look like it wants to play um so we'll just skip it but it's just a short video showing them putting the charge plates on either side and you can see when that cathode ray bends you can always google a video yourself sorry i thought mine would work it works in class it's just not working in this video for some reason all right so protons atoms have no net electric charge they are electrically neutral so if there are negative particles then there must also be positive particles so in 1886 eugene goldstein found evidence for positively charged particles when he found rays traveling in the opposite direction of the cathode ray okay so if we know the cathode ray is negative and something's traveling in the opposite direction of a negative particle then it must have a positive charge however in 1911 ernest rutherford rediscovered them in his gold foil experiment and named them protons all right so depending on what textbook you have some textbooks credit the proton discovery to eugene goldstein some credited to ernest rutherford so just be aware that it just depends on what source you're looking at the electronic charge of a proton like i said is the same as the electron it's just positive so it's positive 1.6 times 10 to the negative 19 coulombs remember coulombs is just a unit for electric charge but we assign it positive one for simplicity so neutrons in 1932 the english physicist james chadwick confirmed the existence of neutrons and remember neutrons are subatomic particles with no charge it's very common for a lot of people to say it's negative because they want to say protons or positive neutrons are negative however neutrons are neutral it's the electrons that are negative so just be careful of that all right so once they started determining some of this stuff so once we figured out hey there's negative particles in here there's electron jj thompson created what we call the plum pudding model of the atom all right so the plum pudding model shows the electrons dispersed in a large positively charged area so i always kind of say it's like you have a large positive force field like think about like a superhero movie where they can create like a force field you have a large positive force field and then you have negative electrons throughout it so this whole pink area is positive there's no nucleus the nucleus had not been discovered yet um and you have electrons throughout and so they call it plum pudding model because apparently there they eat a lot of plum pudding but i like to say it's like a chocolate chip cookie because over here we eat chocolate chip cookies so the cookie part would all be the positive and the chocolate chips themselves would be the negative electrons so there was supposed to be another video i'll assume it's not gonna work but that's okay i talk about what the video talked about anyway so that brings us to rutherford's experiment that's what that video that we just skipped again was on so rutherford decided to test the plum pudding model by shooting alpha particles alpha particles are just helium atoms with no electrons so it's a double positive charge add a thin sheet of gold foil because if plum pudding model was correct the positive areas are just these kind of force fields or blobs of positive area the particles should be able to pass through the foil but deflect or bend slightly because they're going to kind of they're going to kind of bend their path because they're passing through another positive area and of course positives don't like each other but because it's just a positive area not really a particle it should be able to get through but it's just going to kind of change its path a little bit by bending however many of the alpha particles pass straight through like they pass straight through no bending and some of the particles actually hit the gold foil and bounce back if plum pudding model was accurate neither of those things should have happened so this is just a picture of his setup so he has his source of alpha particles which are released through radioactive decay he has his gold foil and then he has a fluorescent screen and what it does is when the particles hit the screen it kind of illuminates a little bit so you can see where the particles are hitting so if you look the straight line is the thickest so most of them pass straight through some of them did bend a little bit and then some of them literally bounced back and so that was his actual result right there so rutherford proposed that since most of them just passed straight through they didn't hit anything so he proposed that most of the atom is actually empty space and that is what we now know as the electron cloud he concluded that all the positive charge must be concentrated and have a high mass in the middle of the atom and that's why some of them literally hit and bounce back they hit an actual particle they didn't pass through some positive force field so he called that the nucleus and then of course the nucleus is the tiny core of an atom and is composed of protons and neutrons so like i said because most passed straight through and didn't deflect at all he determined most of the adam's empty space and then because some of them hit and bounced back he realized it's not like a big positive area it's a small concentrated positive mass in the middle and he called that the nucleus so he's credited with discovering the nucleus so this is just an up close version of what's happening okay so you can see that many pass straight through because they don't come near the nucleus at all you can see the nucleus in the center some of them they kind of deflect that that means they kind of skimmed the side of the nucleus and then the ones that actually bounced back they hit that nucleus dead on and then bounced back from there okay and so all those that just passed straight through they only pass through the electron cloud so after that of course we had to have a more updated version of the atom and that's called rutherford's model so in the nuclear atom or in rutherford's model of the atom the protons and neutrons are located in the nucleus the electrons are distributed around the nucleus and the electron cloud and they occupy most of the volume so the electrons take up most of the space but the nucleus has most of the mass so it's tiny but it's massive the electron clouds are a huge space but they don't have much mass at all all right so let's knock out this section assessment so it says what are the three types of subatomic particles well it's the proton the neutron and the electron proton neutron and the electron so number two how does the rutherford model describe the structure of the atom well the rutherford model has the nucleus in the center the positive nucleus in the center and the electrons in the electron cloud if you want to draw a picture instead of most people they think it's like the jimmy neutron atom so you have your positive nucleus and then our electrons are just kind of somewhere around we're not really sure where in his version yet but we know there's a nucleus that's the important part all right number three it says what are the charges and relative masses of the three main subatomic particles okay so this is just verbal so i'm just gonna say it so a proton has a positive one charge and a relative mass of one a neutron has a zero charge and a relative mass of one an electron has a negative one charge and a relative mass of one over one thousand eight hundred forty all right so number four compare rutherford's expected outcome of the gold foil experiment with the actual outcome so remember he expected the alpha particles to pass through and deflect so kind of pass through and bend in their path that was his expected outcome what actually happened was three things most passed straight through so most of them went straight through perfect straight line some of them deflected like he expected and some of them hit and bounced back okay so he had most passed through some deflected some bounce back all right so let's move on so what experimental evidence led rutherford to conclude that an atom is mostly empty space well remember the fact that some bounced back made him realize that there's a nucleus the fact that most of them pass straight through that's what made him realize it's mostly empty space so for number five you can put most of the alpha particles pass straight through so that means they didn't hit anything positive at all and then number six how did rutherford's model of the atom differ from thompson's plum cutting model okay well the easiest thing to do would be to draw them so plum pudding looks like this a big positive area with negative electrons throughout rutherford's model looks like what we just drew we have a positive nucleus so there's one of the differences and then the electrons are taking up all the space so there's our other difference all right so hopefully again that section wasn't too rough at least in this one we didn't have any math if you're struggling in math um and so in section 4.3 though we're going to focus more on the parts the atom like how many how many protons does something have what is an isotope how do we calculate average atomic mass things like that