ladies and gentlemen welcome to chapter 26. this uh first video will give us a common language to understand what is happening on atomic scale okay so if you're taking chemistry or you remember chemistry this should be you can go through this fairly quickly all right so once upon a time there was this guy called rutherford who did an experiment called the alpha scattering experiment oh the rutherford rutherford experiment sure and you need to roughly know how this setup goes so let's follow along okay so first things first you're gonna have a circular fluorescent screen we'll figure out what why is that so uh and you have a source of alpha particles coming out well we can call it i mean the fat he used americium 241 it's just one of those one of those elements that isotopes that release a lot of alpha particles okay and what are alpha particles by the way just for your information is positively charged so think of it as positive particles positive charge and well it's actually a helium nucleus so this is how you write helium nucleus 4 2h e okay so that's the main idea you are taking a sauce and then what you do with this sauce well you take all these alpha particles and then you shoot it at a thin foil so you go pew pew pew pew pew pew so all these alpha particles will go inside here beam off alpha particles and this tin foil is like really really thin so you try to get it like one layer of gold atoms or so okay anyway so when you shoot it through that uh what happens is uh you will see some alpha particles go follow through and then hit the screen when i hit the screen then it will light up well so what i do is you see in the room and he wait for this fluorescent screen to light up ah that got light okay measure the angle okay so for example if we take this as the vertical if suddenly you see here light up or that's mean here go angle so imagine and girl and they observe the angle and then realize lots of cool things okay so yeah the beam of particles they realize that number one most alpha particles are undeflected means you shoot straight straight away come out pew people just like go to as if like nothing happened and then you shoot through the goal for hmm okay interesting that's one observation the second observation is that oh yo some of the alpha particles are deflected such as maybe this one okay actually let's label this one now okay so i mean go and then a suddenly deflect with some some angle like that from the middle oh so it's like okay some alpha particles are scattered this observation then there are some you notice what really really deflect or like shoot the goal for and then peel fly out this one is like deflect very large angular so deflect with an angle greater than 90 degrees or so okay almost as if you hit something and bounce back so all these ideas um with the food set sat down observed this draw together experiment came with a conclusion and he decided that hmm apparently according to what he discovered all these gold atoms okay gold all this this thing is called gold atoms this round balls okay so the gold atom is probably like this there's probably something in the middle called a nucleus and there's a space around this nucleus which is why sometimes if you have this beam let's say going straight through it didn't hit any nucleus so i just go straight through so that's the observation one observation two sometimes they deflect or why is that like this one here number two see it go kind of like pass through like that number three sometimes if you go inside you hit the nucleus and then you bounce back up that's on the tree law so it's like this is probably what is happening when all these other particles come in and interact with the gold foil so let me jump to here these are the observations that rutherford observe the first one we say most of our alpha particles pass through undeflected while because your atom or is actually mostly empty space so we look at this one up here for example don't be deceiver you see this rumble it's a solid no no no no no actually it's just one nucleus then around there will be electrons so very very small okay and the distance between your i guess your nucleus your first electron is super big like if we put it to scale if i'm a nucleus 10 km away is my first electron swirling around me oh my goodness so mostly empty space okay all this uh thing here oops focusing on nuclear sorry sorry this one empty space okay so nucleus in the middle and then of course all the electrons around then the second observation say why some of the alpha particles come in and then they deflect at the angle like they bend a little bit why well that's because he came with the idea this small angle of deflection is because yes the center of the atom is small but it's positively charged so if you have something like this okay let's say this is your nucleus positively charged so if your alpha particle come in they're all positively charged so maybe for example this one your positive charge come in ear you don't like the other positive charge deflect okay like charges repel because of the electric field of that gold nucleus so yellow that's the second conclusion if you have a positive charge nucleus positive particle come in oh it will deflect and then go away okay so that's the second observation the third observation we mentioned um large angles of deflection right some of it like bounce back and hit something okay or in this case here you see calm bounce and hit something that's because you hit the nucleus itself so that would be for example here you come in then you hit the nucleus which is full of stuff what stuff is it well we'll find out soon and then you bounce back at a very large angle so from that observation rutherford came up with the idea that hmm okay there are large angles i mean we can call large angles more than 90 degrees for example and that is yes the anthem central atom is small only a few la some only i should say not summer a few particles ones in the world central atlanta is very small of course positive charge and very very dense it's full of stuff in there and it's positively charged so your moment you hit the nucleus peel you go backwards so that's why you can have things like perfect reflection wow look at this particle come in hit the nucleus then rebound back at the perfect um 180 angle if you want to call it that way okay so that is your observations and conclusions that come with this thing okay so from this observation rutherford continue and say okay okay i think i know what the structure of the atom is like already middle got stuff very dense or positive charge then later on other people remember the history of the chemistry stuff other people discovered more stuff about the atom so eventually we came to this model structure of an atom okay so here's an example i just picked a random a random element so in the nucleus actually or it's not just positive charge also got this new trauma neutral charge no charge on and they're all stuck together in the middle to form the nucleus and then there will be a number of electrons outside in shells just kind of swirling around the nucleus in the middle this is one model of the atom there are actually many models okay um but never mind that's for quantum physics okay so six protons six neutrons okay this is how the structure of the atom look like now what are protons and neutrons is there a meas proton positive neutral negative okay there's more star to know about that these are the things you need to know uh for physics for proton what is the mass well this is given to you in your your your your data formula sheet you can also find in your calculator do you know how to find your calculator okay so one another way instead of k g sometimes you will say you will see people express it in terms of u so one u is 1.66 times 10 i guess 6 7 is kind of negative 27 kg is just one eula what is u our atomic mass unit of amu you you okay and your proton charge is plus 1 e what is e again a good reminder e is the elementary charge okay uh 1.6 times 10 negative 19 coulombs we have seen this before and also remember please remember charge is quantized means all charge have to be a multiple of this e 1 e 2 e 3 e 4 e because charge is based on these elementary charge units okay and neutron yes what is the mass of a neutron good question neutron is actually the same mass as proton why is it like oh we'll figure it out right in the next next video okay neutrons same size same mass as protons so you can just say the same thing right also one u not one otama by one u times 10 negative 27 kg it's the same thing large mass of proton versus mass of neutron charge length no touch so zero the last one our little baby electron now the electrons are way way way smaller than our proton although in this picture they look kind of the same size right actually electron is much smaller much much much smaller you will get this in your data formula sheet 9.1 times 10 negative 31 kg or an easier way to remember it is proton is 1u right so your electron is 1 over 1 840 u wow where does that come from means your electron is almost 2 000 times smaller than your proton two thousand times smaller it's like okay go ahead and think of something uh find the size of something and find what is two thousand times smaller so it's very very much smaller okay the same thing equal to this and what's the charge well if proton is one e electron is negative one e so one point six well okay negative one point six times ten negative nineteen coulomb that's your uh charge of electron these are the basics you need to know about um what forms the atom what what's in the nucleus what's in an atom all these kind of things so here's some terminology to help us count the protons count the neutrons and the electrons so first thing you know is nuclear number okay nucleon just means what is inside that middle section okay the clamp here what's in the nucleus called nucleon number also is all the protons and neutrons add together and we use this a usually a other other fields may use different alphabets but okay a proton number of causes number of protons inside the nucleus so if you go back to the earlier example our new cloud number will be all this fellow add together also nuclear number uh we call this a will just be 12. proton number how many protons already written there must so that is six the proton number is the one that that means what element it is like the nuclear number let's see what a bit okay so if you want to express this element i call this element x y atom x i can write it this way so x will be you put a neutral number and part proton number down there like this okay so just write what is this and right what is this so for this particular element i can say this element x has a 12 as its nuclear number protons and neutrons and proton number of six oh this looks like what element ah go check your periodic table see what element is this twelve six six six just look for the proton number six anyway one more thing to know is isotopes what are isotopes isotopes are basically nuclei with the same proton number different nucleon number so the same proton number different nuclear number for example carbon so this is an example of what acetyl isotope is same proton number different nuclear number carbon 12 carbon 13 carbon 14. what's the difference there you see how the proton number of all of them is the same six six six that's what make them carbon okay six protons but then the neutrons six seven eight so this other fellows got extra neutrons are okay here and here so this is what we call isotopes okay this is this is the most common one on the natural state 98 of it okay the rest are if they happen to have extra neutrons then they become then they are isotopes okay so that's all for today's this video's uh basics on terminology how to think of nucleons protons and things like that all right so yeah that's all for today on the next video we will look at nuclear reactions okay and continue to that but this is it basics structure of the