The video explains atomic structure, starting with ancient Greek theories and Dalton's atomic theory. It details the discovery of subatomic particles (electrons, protons, neutrons) through experiments like Thomson's cathode ray tube and Rutherford's gold foil experiment. Isotopes (atoms with varying neutron numbers) and ions (charged atoms) are also discussed, emphasizing how proton number defines an element and neutron number affects its mass and stability. The video explains atomic structure, starting with ancient Greek theories and Dalton's atomic theory . It details the discovery of subatomic particles (electrons, protons, neutrons ) through experiments like Thomson's cathode ray tube and Rutherford's gold foil experiment. Isotopes (atoms with varying neutron numbers) and ions (charged atoms) are also discussed, emphasizing how proton number defines an element and neutron number affects its mass and stability. Discovery of The Electron one, which most of us are familiar with. It has only been a decade or so, uh, since that large, heavy, nearly cube-shaped television vision set finally gave way to the slim energy sipping displays that adorn the walls of your favorite big box stores.09:06But the technology on which these household devices of the late 20th century were based actually was devised much earlier. The cathode-ray tube, or CRT, as it is sometimes called, was actually developed at the end of the 19th century. And it played an important role in the advancement of human understanding of atoms. Rutherford's gold foil experiment, designed to build upon Thomson's Plum Pudding model, ended up disproving it. Here's how: Thomson's Plum Pudding Model: This model envisioned the atom as a positively charged sphere with negatively charged electrons embedded within it, much like raisins in a pudding. Rutherford's Experiment: He bombarded a thin gold foil with alpha particles (positively charged particles). Expected Outcome: Based on Thomson's model, Rutherford expected the alpha particles to pass through the foil with minimal deflection. Unexpected Results: Most alpha particles did pass straight through, as predicted. However, a small fraction of alpha particles were deflected at large angles, and some even bounced back in the direction of the source. This outcome was inconsistent with the Plum Pudding model, which could not account for such significant deflections. Challenging the model: The experiment was intended to build upon Thomson's model. Instead, it disproved the Plum Pudding model outright. Conclusion: Rutherford's experiment led to the understanding that atoms have a dense, positively charged nucleus, with electrons orbiting around it, a concept that replaced the Plum Pudding model. That is, there must be some point beyond which we cannot go in the division of matter, I have chosen the word atom to signify these ultimate particles. But Dalton believed that he had reached the end of the story. In his mind, atoms were the ultimate particles of matter, and nothing smaller could exist That is, there must be some point beyond which we cannot go in the division of matter, I have chosen the word atom to signify these ultimate particles. But Dalton believed that he had reached the end of the story. In his mind, atoms were the ultimate particles of matter, and nothing smaller could exist. That is, there must be some point beyond which we cannot go in the division of matter, I have chosen the word atom to signify these ultimate particles. But Dalton believed that he had reached the end of the story. In his mind, atoms were the ultimate particles of matter, and nothing smaller could exist. But Rutherford is not most famous for discovering these particles. he's most famous for what he did with them. Next, Rutherford was curious to know how these relatively large energetic alpha particles would interact with atoms as they passed through a thin FOIL of atoms 1932 when James Chadwick, formerly a student, UH, of one of rutherford's own assistants, completed the inventory of subatomic particles Chadwick reasoned that this newly discovered radiation was able to penetrate other atomic nuclei better because it was uncharged where, whereas alpha particles used by Rutherford carried positive charge and were repelled by the positive nuclei of the atoms, they struck. This explains their tendency to ricochet and bounce back. But these new particles, though massive, were able to get deep inside the nuclei, they struck without bouncing back. they had to be uncharged. The lack of an electrostatic repulsion allowed these new particles to strike those nuclei with great force, a force that Chadwick used to estimate their mass. And he dubbed these particles neutrons. And quite interestingly, he discovered that they were just a fraction of a percent larger than protons themselves, Because protons and neutrons are so similar in mass and so much larger than electrons, they contribute nearly all of the mass to an atom. Chemists use a unit of mass called the atomic mass unit, or AMU to compare masses of atoms to one another. And protons and neutrons themselves, each weigh just about one atomic mass unit. So this very convenient unit of measure leads to a nice round number for communicating the mass of an individual atom. So by 1932, the combined thought of ancient greeks, Dalton Thompson-Rutherford and Chadwick, and of course, many, many others had led us to an understanding of an atomic structure that looks something like what you see today, in popular depictions of the atom. let's start with the simplest atom of all, an atom of the element Hydrogen. Now, all atoms consist of that dense central core of matter, called the nucleus. And in that nucleus, we always find one or more protons. And in the case of hydrogen, we have just one around that dense positively charged core are electrons. And again, in this case, we have just one electron to balance the positive charge from the proT in the nucleus. This is a complete hydrogen atom uh complete with a proton at the center and an electron orbiting. Now, we sometimes refer to this version of hydrogen as proteum, because its nucleus contains just a single proton. Now, remember, don't let this scale fool you. Here, I have drastically increased the size of that nucleus to make it easier to see if the atom were really this size, the nucleus would actually be about the size of a grain of sand. but we need to see what's going on here. So, I've increased it. Now, it's the proton count in the nucleus that gives an element its identity. So I can add a neutron to my construct here. And I still have hydrogen, but now my hydrogen atom is twice its original mass. So we call this type of hydrogen one, in which a neutron is also present, derium, this is more massive, and Prodium, I can increase the mass of derium yet again by adding another neutron to it to get what we call tritium, another Radiation if we add one extra electron to it, we get what's known as a fluoride ion. An additive sometimes included in toothpaste or drinking water. To help strengthen your teeth, we can create an ion with an even greater charge by adding even more electrons. Uh, consider oxygen. For example, if we add two electrons to oxygen, we get what is commonly called an oxide ion. This is the form of oxygen that we find in rusted metal. For example. let's take a look at sodium. Now with 11 protons and electrons, we can remove an electron from sodium, creating a positively charged sodium ion that charged sodium ion, not the neutral sodium atom, is that pesky form of sodium that your doctor keeps telling you to cut down on in your diet and just like like anion, cations can carry greater charge When the discrepancy between electrons and protons is greater. For example, magnesium would have 12 electrons as a neutral atom. but when found in rock-forming minerals like limestone, those magnesium atoms are missing two electrons forming a cation with a plus two charge. So let's take a moment now and review what we have discussed so far. We started out considering how nature uses combinations of smaller, simpler components to create tremendous variety in a wide range of scales from galaxies to biological systems. We saw how atoms are not so different, having only three components called subatomic particles, protons, neutrons, and electrons. we saw how protons and neutrons reside at the center of the atom in its nucleus, giving the atom most of its mass, and how electrons orbit that nucleus, balancing out the positive charge at the atom center. Then, we talked about the ancient Greek philosophers in their debate over the most basic components of matter, which led to the coining of the term atom, meaning indivisible. We saw how this term falls short in describing atoms as we know them today, but its deep history in the discussion has led us to keep its namesake for the building blocks of the elements. Next, we took a look at how the work of John Dalton, reignited the discussion about atomic theory 2,000 years after it was first proposed and how he did this, by considering the law of conservation of mass and the law particle and cause it to ricochet backwards in its original direction. Rutherford's own words probably best describe this. He famously recounted of his own experiment. it was quite the most incredible event that has ever happened to me in my life. It was almost as incredible, as if you had fired a 15-in shell at a piece of tissue paper, and it came back and hit you. So there had to be an extraordinarily dense but vanishingly small point of mass at the center of atoms very dense, to explain the ricocheting alpha particles and vanishingly small, to explain why just a handful of those ricochets took place during Rutherford's experiment. Rutherford realized then that atoms were mostly made of empty space with that dense point of matter at their center. His model accounts for this and has been dubbed the Rutherford model, sometimes also called the nuclear model, because it's the first to acknowledge that most of an mass resides in that small dense nucleus at its center. So, Rutherford had discovered that atoms consisted of dense, positively charged nuclei surrounded by very light, negatively charged electrons, but just how small is a nucleus, really. Now recall that we've already learned just how small atoms are having diameters of about 100 pomers, that's about 1/1 of a nanometer. Now Rutherford's work eventually to discovery that the this perpetually, eventually, we would arrive at a point where we have just one atom of gold left in our sample. So what now is that atom of gold truly indivisible? Actually, no, it can be divided. But in doing so, its identity changes, the two fractions created by splitting an atom of gold are no longer gold, they're something else. But this leads us to an interesting question, What are atoms themselves made of? If they can be split into other smaller atoms, then they must be made of even smaller pieces of matter than atoms themselves. And in fact, they are, atoms are comprised of just three types of particles, called subatomic particles, positively charged protons, negatively charged electrons, and neutrons, which have no charge at all. protons, and neutrons are of nearly equal mass and reside in a dense nucleus at the center of the atom, but much smaller, negatively charged electrons orbit that nucleus, balancing out the positive charge that's provided by the protons. Most of us are familiar with this depiction of the atom. but the story of how we came to understand it is every bit as fascinating as the structure's own elegance. So, today, we're going to try to understand how each of these particles was discovered and how generations of scientific work ultimately came together to create our understanding of the most fundamental unit of matter. The atom, The notion of atoms was first forwarded by ancient Greek philosophers who postulated that there are just a handful of fundamental substances Now, they combine in various ways to form all other substances. ut we need to see what's going on here. So, I've increased it. Now, it's the proton count in the nucleus that gives an element its identity. So I can add a neutron to my construct here. And I still have hydrogen, but now my hydrogen atom is twice its original m