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Atomic Structure
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About the lecture
In this mini-lecture, we introduce atomic structure, focusing in particular on: (i) the atomic structure of the hydrogen atom, through which we introduce the proton, neutron, and electron; (ii) isotopes of elements; (iii) a brief interlude on the fundamental particles of nature from the Standard Model; (iv) models of the atom, including the Plum Pudding Model and the Nuclear (or Solar System) Model: (v) Ernest Rutherford’s gold foil experiment that tested the Plum Pudding Model and showed that the Nuclear Model was more accurate; (vi) a demonstration of the gold foil experiment; (vii) the emission spectra of elements, specifically that of hydrogen known as the Balmer series; (viii) a hydrogen lamp that illustrates the Balmer series; (ix) orbits of electrons and how electrons move between energy levels; and (x) atomic subshells.
About the lecturer
Janet Lovett is a Lecturer in the School of Physics and Astronomy at the University of St Andrews. Her primary research interest is in measuring nanometre distances for structural biology using Electron Paramagnetic Resonance (EPR) spectroscopy. Dr Lovett teaches a first-year ‘Properties of Matter’ course at the University in addition to other courses such as magnetic resonance.
Hi, My name is Dr Janet. Love it.
00:00:05I'm a lecturer in the School of physics
00:00:08and astronomy at the University of ST Andrews.
00:00:11In this section, we're going to be looking at atomic structure.
00:00:14The hydrogen atom is the most simple element
00:00:18we define as having one nuclear or particle that makes up its nucleus.
00:00:22And we call this a proton.
00:00:28The Proton has a single unit of positive charge.
00:00:30The hydrogen atom has no charge. It's neutral,
00:00:35and that's because the single positive charge from the proton
00:00:38is balanced by the charge of a single electron.
00:00:41The electron has the same charge, the opposite in sign,
00:00:45but it's nearly 2000 times less mass.
00:00:49Both the proton and the electron.
00:00:52A tiny, though, and if you had one gramme of hydrogen, you would have one mole of it.
00:00:54And this is more than 600,000 billion billion atoms.
00:01:00All the elements are made up in a similar way. They have nuclear.
00:01:06I made of protons and neutrons,
00:01:10neutrons of particles pretty much the same size as protons that have no charge.
00:01:12They contain as many electrons as protons to balance out the charge
00:01:19isotopes of the elements just have varying number of neutrons in the nucleus,
00:01:24but the same number of protons and therefore electrons as all the other isotopes
00:01:29of a given element.
00:01:34The protons and neutrons that make up the nuclear of atoms are Barry ins,
00:01:38and this means that they are made up from more fundamental particles.
00:01:42These include quarks, which you may have heard of.
00:01:45The electron is, however, already a fundamental particle,
00:01:49and it's classed in the standard model of particle physics.
00:01:52As a Lipton, I'm not going to go into more detail of this yet,
00:01:55but just to give you a flavour of the start of particle physics,
00:01:59we usually think of the nucleus as being at the centre of orbiting electrons.
00:02:05So in this simple picture of a P and E,
00:02:10we would have our electron circling around our protons in the hydrogen atom.
00:02:13But how was this picture derived? Where does it come from?
00:02:20A scientist called Ernest Rutherford
00:02:24proposed the original solar system model in 1911 because experiments showed
00:02:27that the existing best model at the time,
00:02:32which was called the plum pudding model,
00:02:35was not correct.
00:02:38In the plum pudding model,
00:02:40there is a pudding of positive charge
00:02:42and plums of negative charge in it.
00:02:44The experiments showed that in fact,
00:02:48there must be a small and dense region of positive charge
00:02:49in the centre of an atom,
00:02:53and this was called the nucleus of the atom.
00:02:55The electrons now orbit around this somewhat like planets around the sun,
00:02:59but attraction is through electrostatic charges rather than gravity.
00:03:04In the experiments, small, dense,
00:03:09positive charges called alpha particles were fired at gold foil
00:03:11in the plum pudding model.
00:03:16The fast,
00:03:17dense alpha particles would just pass through the diffuse pudding of
00:03:18positive charge that made up each of the gold atoms.
00:03:22There might be a bit of deflection, but not much.
00:03:26However,
00:03:29What was actually seen in the experiment was that while
00:03:29most of the alpha particles passed through the foil,
00:03:33some were deflected quite a lot and some bounce straight back towards the source.
00:03:36This was not consistent at all.
00:03:41It could, however,
00:03:44be explained if all the positive charge of the gold was densely packed in
00:03:45each atom and that most of the rest of the space was empty.
00:03:48We're going to look at an experiment
00:03:52to demonstrate the gold foil experiment. Now
00:03:55this demonstration is a simplified representation of the gold foil experiment.
00:04:00The yellow balls represent the nuclear of the gold atoms,
00:04:06and the Grable's are the particles that are going to be fired at the foil
00:04:10and so we can see that
00:04:16some pass through
00:04:19and
00:04:21some are
00:04:22deflected,
00:04:24Um, and even bounced right back like this one.
00:04:25And that wouldn't have happened if the plum pod
00:04:30if the plum pudding model had been right.
00:04:32By the way.
00:04:35We now know that the gold atoms nucleus is made up of 79 protons and 118 neutrons.
00:04:36The alpha particle is actually the same as the nucleus of
00:04:42helium and is made up from two protons and two neutrons.
00:04:45The problem with the solar system model of the
00:04:50electrons orbiting the sun like nucleus means that electrons
00:04:52are not planets held in orbit by gravity but
00:04:56the charged particles moving in a curved path.
00:04:58This must release energy,
00:05:01and this must mean that atoms are not stable.
00:05:03Meanwhile,
00:05:07astronomers had found that different elements could
00:05:08be identified through their emission spectral fingerprints.
00:05:10Hydrogen, for example,
00:05:13has a spectrum which gives visible light called the bomb a series.
00:05:15The Planetary model didn't show why
00:05:20atoms have emission spectra.
00:05:23In fact,
00:05:25starting to understand emission spectra was a really important step
00:05:26towards our understanding of the quantum nature of the universe.
00:05:29In the hydrogen lamp or in a star, the hot hydrogen electron has a lot of energy,
00:05:34and as it cools down, it gives out energy,
00:05:41and this corresponds to the electromagnetic spectrum.
00:05:44So photons are released.
00:05:47Now only certain wavelengths of photons are released.
00:05:51Their energy is quantized.
00:05:54In 1913,
00:05:57Neil Bohr modified the planetary model so that
00:05:59the electrons could only have certain orbits.
00:06:02They can circulate in these orbits without radiating energy.
00:06:05But for an electron to move between orbits,
00:06:09energy needs to either be put in or given out.
00:06:12So we have our small, dense nucleus in the middle,
00:06:16and then we have our orbit of electrons.
00:06:20So what we see in the emission spectra is the electron
00:06:25cooling and jumping between levels hopping down towards the nucleus.
00:06:29In the Bombers series, the photon corresponds to a colour of light,
00:06:35with higher energy jumps giving out purple or blue light
00:06:38and lower energy jumps giving out red light.
00:06:42In this case, the electrons are all jumping back into the orbit,
00:06:45which is the second closest to the nucleus.
00:06:47Now we know that the Bohr model is too simplistic
00:06:51and was based too much on classical physics.
00:06:55It is better to think of orbital's having different energies and different shapes.
00:06:58Each of the orbital's of a given energy and shape, which we often call a sub shell,
00:07:02can hold just two electrons.
00:07:06Now, this is a property of the quantum mechanical nature of the electron,
00:07:09and I won't go into this during this course but can be
00:07:14summarised by the term spin should you want to find out more.
00:07:18The way these sub shells are filled is determined by their energy,
00:07:23with the lowest energy being filled first.
00:07:27And this depends upon what shape they have and
00:07:30what charged the nucleus of the atom has.
00:07:32Basically,
00:07:35the energy and type of orbital at the highest
00:07:36energy of an atom determines the atoms chemistry.
00:07:38There is a systematic filling of these sub shells,
00:07:42and this is why the periodic table predicts chemical properties.
00:07:45So that's the end of this section. We looked at the structure of the atom.
00:07:50We didn't really look at electrons,
00:07:55and in the next lecture we're going to be looking at the electron and,
00:07:58more specifically, the discovery of the electron
00:08:01
Cite this Lecture
APA style
Lovett, J. (2022, January 12). 7. Atomic, Nuclear and Particle Physics - Atomic Structure [Video]. MASSOLIT. https://massolit.io/options/7-atomic-nuclear-and-particle-physics?auth=0&lesson=4477&option=14522&type=lesson
MLA style
Lovett, J. "7. Atomic, Nuclear and Particle Physics – Atomic Structure." MASSOLIT, uploaded by MASSOLIT, 12 Jan 2022, https://massolit.io/options/7-atomic-nuclear-and-particle-physics?auth=0&lesson=4477&option=14522&type=lesson