Pratique du Shadowing: GENERAL CHEMISTRY explained in 19 Minutes - Apprendre l'anglais à l'oral avec la vidéo
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298 phrases
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Everything is made of atoms.
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Yes, even you.
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Atoms consist of a core and some electrons.
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The core is made of protons and neutrons, and depending on the number of protons, you get different elements.
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Water is made of hydrogen and oxygen.
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This is some sodium.
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Hmm, I wonder what happens when you...
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Ha, whoopsie.
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Quantum mechanics tells us that this is not what atoms actually look like.
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They look more like this, but we'll get to that later.
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For now, just think of atoms as having multiple electron shells.
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The electrons in the outermost shell are called valence electrons.
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Most of chemistry is really just the behavior of these electrons.
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Every element is listed in the periodic table.
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All elements in the same column or group have the same number of valence electrons.
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For the main groups, the number of valence electrons is just the group number from 1 to 8.
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Except for helium.
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It's too small to have 8 electrons, it can only have 2, but still, it acts like a noble gas,
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so it's just kinda grouped in with those.
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Luckily, the transition metals also follow a nice pattern.
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That was a lie, it's kind of a mess, but that's not so important for now, so we'll get to that later.
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Elements with the same number of valence electrons tend to show similar behavior in chemical reactions.
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For example, the first group without hydrogen is called the alkali metals.
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Here's some things they have in common.
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They have one valence electron, they're shiny metals, they're kind of soft, and they do this sometimes.
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All elements in the same row or period have the same number of shells.
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This number increases from top to bottom.
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Also, the mass gets bigger from left to right, as each element gains a proton, an electron, and some neutrons.
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Depending on the number of neutrons in the core, you get different isotopes of the same element,
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most of which are pretty unstable and fall apart, releasing ionizing radiation.
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Fun fact, that stuff will kill you.
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If an atom has the same amount of electrons as protons, it has no charge.
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If it has more, it has a negative charge, and if it has less, it has a positive charge.
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Charged atoms are called ions.
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Negative ions are anions, and positive ions are cations.
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The periodic table is also pretty much a dictionary, as every cell tells you the name and symbol of an element,
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the number of protons in the core, which is also the total number of electrons,
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and the atomic mass, which is the mass of neutrons and protons combined.
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The periodic table is roughly divided into three categories.
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Left of this line are the metals, right of it are the non -metals, which are mostly gases, and the line is called the semi -metals,
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which have properties that fall somewhere in between.
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Two or more atoms bonded together form a molecule.
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If you have at least two different elements, you get a compound.
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Oh yeah, this is probably a good time to mention that compounds often behave completely differently than the elements they're made of.
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Like you put together an explosive metal and a toxic gas, and you get, of course, an even more expli - Table salt.
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You get table salt.
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There's many ways to write molecules, for example the molecular formula, where you just count the number of each atom in a molecule
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and write them as a subscript number next to the element symbol.
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But that has some problems, look at these two molecules.
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They have the same molecular formula, but obviously they're not the same.
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They're isomers.
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Showing this difference is probably kind of important, it's the only thing that separates graphite from diamonds, because they're both just fancy versions of carbon,
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and I don't think anyone's gonna go, well, yes, this dusty black blob is indeed very expensive.
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One way to show the structure of an atom is a Lewis dot structure, which represents the valence electrons and bonds as dots and lines.
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This is also going to help us understand why atoms bond in the first place.
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You see, everything in the universe wants to get to a state of lower energy.
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That's why a ball on a hill will roll down by itself, because that decreases its potential energy.
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This trend also applies to atoms.
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The state of lowest potential energy is having a full outer shell of electrons, which is most often eight,
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or in the case of hydrogen and helium, too.
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If you think back to the periodic table, you'll see that all noble gases already have a full outer shell,
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which is why they don't really want to react with anything.
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If two atoms don't have a full outer shell, but can achieve one by sharing electrons, they will naturally do so,
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the same way a ball will go downhill, as their combined energy would be lower than if they were separate.
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The sharing of electrons is called a covalent bond.
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These bonds are also caused by the positively charged nucleus of an atom tugging on electrons of another atom.
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The strength of this pole is called electronegativity.
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In the periodic table, the electronegativity increases from bottom left to the top right.
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Therefore, fluorine has the strongest pull.
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It's just unbelievably desperate for an electron.
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If the difference in electronegativity is bigger than about 1 .7, you get an ionic bond.
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A good example is sodium chloride.
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Chlorine would do anything for an electron, while sodium has one too many and just kinda wants to get rid of it anyway.
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Perfect, they both say, forming an ionic bond, where sodium loses an electron and turns into a cation,
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and chlorine gains an electron and turns into an anion.
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That seems pretty important.
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You might want to remember it.
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The most common place you see ionic bonds is in salt.
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Yes, also table salt, but more generally when metals and non -metals bond you get a salt, which is just a grid of ions.
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Speaking of metals, a pure metal forms metallic bonds.
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You can imagine this as a huge grid of positively charged nuclei, which are surrounded by freely moving electrons.
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You see, in a metal grid, the valence electrons are kinda promiscuous, or as the nerds call it, delocalized.
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They can move freely in a giant playground of nuclei instead of being loyal to just one.
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This kind of bond is responsible for the properties of metals, like conducting electricity and heat, and also being malleable, as in being kind of bendy.
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Like, you can hammer on this stuff until it's the most deformed, unelegant, and ugly -looking piece of material ever known,
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and it will just limp along as if nothing ever happened.
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If the difference in electronegativity is lower than about 0 .5, the electrons are shared pretty equally and you get a non -polar covalent bond.
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If it's bigger than 0 .5 but smaller than around 1 .7, one of the elements is pulling on the electrons pretty hard.
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Not quite hard enough to completely steal an electron, but definitely hard enough to skew the electrons a bit, making it a polar covalent bond.
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An example is water.
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Oxygen has a very high electronegativity compared to hydrogen.
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As a result, it pulls the electrons of hydrogen so hard that they kind of belong to oxygen, giving it a partial negative charge,
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and leaving hydrogen with a partial positive charge.
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The presence of two poles with opposite charge is called an electric dipole.
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All permanent dipole molecules can interact with each other, and really with anything that has a charge.
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As a result, the molecules will tug on each other
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and arrange themselves in a way that oppositely charged ends are next to each other.
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The forces acting between them are called intermolecular forces, or IMFs.
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A specific example is hydrogen bonds, where hydrogen bonds to something very electronegative, like fluorine, oxygen, or nitrogen, creating strong dipoles that tug on each other.
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But even if molecules are not polar at all, there can be electrostatic forces acting between them.
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How?
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Electrons move around inside the atoms, and by pure chance they can end up on one side of the atom,
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creating a momentary dipole, which influences other particles next to it to become a dipole as well.
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At least for a very short time, as the electrons keep moving and the dipole disappears.
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This is called the van der Waals forces.
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The polarity of water also explains why it's one of the most versatile solvents to exist.
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It can pull apart molecules by tugging on charges, and it keeps them apart by surrounding a particle with its oppositely charged end.
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Water cannot dissolve non -polar molecules though.
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It's the reason why water and oil don't mix, since fat molecules are non -polar while water is polar.
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Just remember the ancient saying, Similia similibus solventum.
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Or in the language that's actually spoken, similar things will dissolve similar things things.
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Fun fact!
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Soap works because the molecules that it's made from, which are called surfactants, have a polar head and a nonpolar tail.
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This way, when in water, they can surround for example nonpolar fat molecules and form micelles, which along with the water, transport the dirt particles away.
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These are the most important bonds and forces ranked by strength.
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Ionic bonds, covalent bonds, metallic bonds, hydrogen bonds, and van der Waals forces.
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There are three main states of matter.
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Solid, liquid, and gas.
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Solids are tightly packed in fixed structures, where the particles can only wiggle.
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Unless, you know, you smash them.
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In liquids, the particles can move freely but are still confined to a fixed volume,
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as the forces between them are still strong enough to keep them together.
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And the particles and gases have enough energy to just do whatever they want
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and fill up all the volume you give them.
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Knowing this, we can find two important words.
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Temperature is the average kinetic energy of particles in a system, or how much and how fast they move, and entropy is the amount of disorder.
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Substances tend to be solid at low temperature and or high pressure, which is a state of low entropy,
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as they're neatly organized and don't move that much, and gas at a high temperature and or low pressure,
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where they move around like crazy so it's a state of high entropy.
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Strong bonds like ionic bonds lead to high melting points, as they take a lot of energy and therefore a high temperature to break apart.
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That's why most salts are solid at room temperature, whereas water, which is only being held together by hydrogen bonds, is a liquid.
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Well actually, there's another state called plasma,
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which is ionized gas and can exist at very high temperatures such as in stars or very high electric potential.
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The latter is used for neon lights.
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Gas is ionized in a tube with a very high voltage.
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Collisions of the ions with other particles makes their electrons move to a higher energy state.
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Once they fall back down, the difference in energy is released as light.
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The color of the light depends on the element that's used in the tube, as each element has different but fixed energy levels,
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and the difference between those determines the energy and therefore the frequency of the released light, which is what changes the color.
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All possible frequencies that an element can emit are called the emission spectrum.
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All matter can be divided into two categories pure substances, which can consist of one element or one compound, and mixtures.
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Mixtures consist of at least two pure substances and can be homogeneous or heterogeneous.
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Homogeneous means the substances we'll mix evenly and the mixture looks the same everywhere, like salt and water, which is a solution.
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Heterogeneous mixtures look different depending on where you look.
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They have distinct regions made of separate substances.
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One example is sand and water, which is called a suspension.
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Okay, well what about milk?
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That looks the same everywhere, so it must be homogeneous.
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Uh, no, milk is something we call a colloid, or more precisely, an emulsion.
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The difference between salt water and milk is that the solute doesn't fully dissolve in the solvent, meaning there are bigger particles than in a solution,
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but smaller particles than in a suspension.
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This allows the particles to stay evenly distributed, but not fully dissolved, placing them somewhere between solutions and suspensions.
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Hey, remember sodium and water?
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What's going on there?
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Explosions are really just chemical reactions that release a lot of energy in a very short amount of time.
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Also, they expand.
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Like, a lot.
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There's a couple types of chemical reactions.
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Synthesis, decomposition, signal replacement, and double replacement.
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Here's an example for each one.
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They all happen mainly for one reason, to decrease energy and get to a more stable state.
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Chemical reactions happen in certain ratios.
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For example, to produce water molecules you need twice the amount of hydrogen compared to oxygen.
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This is called stoichiometry.
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These ratios are based on the conservation of mass, which says that mass cannot be created or destroyed, only converted.
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Practically, when dealing with reaction equations, you have to make sure that there's the same amount of atoms on each side of the equation,
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and if not, balance it out element by element.
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As a rule of thumb, you should balance out the metals first, then the non -metals, and then hydrogen and oxygen at the end.
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But it's really just trial and error until everything is balanced.
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Okay, but if you wanted to make this reaction happen in a lab,
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how would we know that we have exactly twice the amount of hydrogen compared to oxygen?
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You can't just take 10 grams of this and mix it with 20 grams of that, because the atoms don't weigh the same,
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so 10 grams of both contain a different amount of particles.
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What to do?
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Just look up the atomic mass of the reactants and take that amount in grams.
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You'll get exactly this amount of particles.
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That is one mole, which is just an amount of something, kind of like a dozen.
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In other words, we can interpret the reaction as two moles of this react with one mole of that, which we can easily measure.
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It's important to differentiate between physical and chemical changes, as reactions only take place in the latter.
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Physical change happens when the appearance changes, but the substance does not.
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For example, hammering metal.
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A chemical change happens when the substances themselves change, and this is often accompanied by bubbles, a funky smell, or, you guessed it, explosions.
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All chemical reactions need activation energy to take place.
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Wood won't just spontaneously react with oxygen and start burning, or else, you know, the planet would be on fire,
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but if you give it enough energy, it will.
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Catalysts reduce the activation energy needed for a reaction, which makes it happen easier and faster.
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And as a neat bonus, they don't even get used up during the reaction so you can just reuse them.
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Because chemical reactions are changes in energy, it's quite useful to keep track of it.
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Enthalpy is, simply put, the internal energy or heat content of a system.
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If the total enthalpy of a reaction is lower at the end than at the beginning, heat was given off to the surroundings,
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which is an exothermic reaction.
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If it's the other way around, a reaction is endothermic.
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It's easy to see how exothermic reactions can be spontaneous.
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It's kind of like a ball on a hill.
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It will only start rolling if you push it a little bit, but then it will keep rolling on its own.
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Just like wood keeps burning on its own.
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But in endothermic reactions, you have to keep putting in energy, like pushing a ball uphill.
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That doesn't just spontaneously happen, right?
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Well, yes, actually it does.
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To get the whole picture, we have to look at Gibbs free energy, which looks at the change of enthalpy,
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but also the entropy of a system, which is dependent on temperature.
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If this whole thing is less than zero, the reaction is exergonic, or spontaneous, because free energy was released.
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If it's bigger than zero, it's endogonic, or not spontaneous, because free energy was needed and absorbed.
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Here's where temperature and entropy come into play.
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Even if delta H is positive, so the reaction is endothermic, if the change in entropy is big enough,
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it can offset this and make the total free energy negative, which means the reaction is spontaneous.
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But this is strongly dependent on the temperature.
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For example, melting an ice cube is endothermic, because it absorbs heat.
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But also, it increases the entropy a lot, as neatly organized ice turns into water, which is just kind of a mess.
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So this can happen spontaneously, but only if the temperature is above zero.
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If it's below zero, the water will spontaneously freeze, which is exothermic.
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If it's exactly zero, then no reaction will take place spontaneously.
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In other words, if delta G is zero, we're at equilibrium.
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Chemical equilibriums exist when reversible reactions take place at the same speed in both directions, which means that even if reactions are taking place,
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the concentrations of both sides stay the same, and to someone watching from the outside, nothing seems to be happening.
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We often find chemical equilibriums in phase changes, but also acid -base chemistry.
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According to Branstad -Lowry, an acid is a molecule that donates protons, while bases accept protons.
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A proton in this case is just a hydrogen ion.
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So, with this definition, a molecule with at least one hydrogen that it can throw away can be an acid,
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and anything that can pick it up can be a base.
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This also means that once they react, they turn into the conjugate opposite, as an acid that gave away a proton can now accept one back,
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which is what bases do.
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A molecule that can act as both an acid and a base is amphoteric, for example water.
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A strong acid will dissociate almost completely into its ionic form,
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giving off a lot of protons to the water and therefore creating lots of hydronium ions.
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A weak acid just won't dissociate nearly as much, giving us a lower concentration of hydronium ions.
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So, to measure the strength of an acid we can measure the concentration of hydronium ions.
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This is called the pH.
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Mathematically, it's defined as the negative log of the hydronium concentration, which means one step on the scale is a 10 times change,
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and also, since it's a negative log, the higher the concentration, the lower the pH.
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For example, pure water is in a chemical equilibrium.
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There is exactly one hydronium ion for every 10 million water molecules.
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In other words, the concentration of hydronium is 1 over 10 million, or 1 times 10 to the negative 7.
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Taking the negative log of this gives us a pH of 7, which is considered neutral.
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Anything lower than 7 is acidic, and anything above is basic, unlike you.
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You can do the same thing with hydroxide ions and you will get the pOH, which keeps track of basicity.
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Fun fact, the pH and pOH will always add up to 14 because they counteract each other, so by knowing one, you know both.
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Now, if you have a strong base and a strong acid and you pour them together, no, they will not explode.
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They will neutralize by forming water along with the salt, which is neutral.
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For example, hydrochloride and sodium hydroxide will form water and table salt.
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Oh yeah, speaking of table salt, remember how it consists of ionic bonds because sodium transfers an electron to chlorine,
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well that is called a reduction oxidation reaction or redox.
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If sodium chloride forms out of its pure elements, the sodium gets oxidized as it loses an electron,
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and the chlorine gets reduced as it gains an electron.
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Logically, sodium is the oxidant, and chlorine is the reductant.
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Of course not, that would make sense, it's the other way around.
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More accurately, redox reactions are reactions that change the oxidation numbers of elements, which are kind of like imaginary charges.
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There's just a few rules you have to know to figure those out.
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Hydrogen is mostly plus one.
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Oxygen is mostly negative two.
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Halogens are mostly negative one single elements are always zero
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and the number of all atoms in a molecule always have to add up to the molecules charge.
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So this would total zero while single ions just have their charge as the oxidation number.
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For example in sulfuric acid we have four oxygens which totals negative eight, we have two hydrogens which brings the total to negative six,
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and since the whole molecule is neutral sulfur must have an oxidation number of plus six.
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Just by looking at the oxidation numbers of reactants
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and products you can deduce the flow of electrons which gives you these equations.
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If redox reactions happen in acidic or basic solutions, you can balance out the charges with ions and fix the stoichiometry with water.
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Okay, now to this weird -looking thing.
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I spared you from it because for describing electrons, this is very simple and this is not.
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But this is actually like pretty wrong.
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Electrons don't orbit in circles.
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Here's how it actually works.
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All electrons inside an atom are described by four quantum numbers.
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N, L, ML, and MS. N corresponds to the shells, so all electrons with the same N are in the same shell.
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Within the shells, we have subshells with multiple orbitals, which are three -dimensional regions in space where electrons could be.
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We know these exist thanks to Schrodinger's equation, which gives a probabilistic wave function.
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You can imagine it as a cloud, and the denser it is,
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the more likely an electron is to be there if we were to look for it.
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L describes the shape, and ML the orientation of orbitals in a subshell.
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There are four subshells called S, P, D, and F.
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If electrons have the same L, they're in the same subshell.
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If electrons have the same N, L, and ML, they're in the same orbital.
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Also, the number of orbitals increases by 2 for every bigger subshell, starting at just 1 for S.
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The last quantum number describes an intrinsic property of electrons called spin, which can have two values.
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Some guy named Pauli said two electrons can never have the exact same quantum numbers inside one atom.
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Since MS can only have two values, every orbital defined by N, L, and ML can hold a maximum of two electrons with opposite spin.
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Therefore, the S subshell can hold two electrons, the P subshell can hold 6, D can hold 10, and F can hold 14.
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Now, the quantum numbers restrain each other like this, which means that the first shell can only have an S subshell,
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the second can have an S and a P subshell, and so on.
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This means that the first shell can hold a total of two electrons, the second can hold eight, the third can hold eighteen,
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and generally the number of electrons a shell can hold follows the rule 2n squared, with n being the principal quantum number.
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The principal quantum number, and therefore the total number of shells, increases from top to bottom in the periodic table, from one to seven.
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Every element has a different number of electrons that fill up these orbitals,
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and the different subshells and orbitals are filled in a specific order called the Aufbau Principle.
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Just write down the subshells like this, and draw diagonal lines from top right to bottom left.
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To get an electron configuration,
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just look up the number of electrons of the element in the periodic table and fill up the subshells in this order,
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until there are no electrons left.
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This would be the electron configuration of sodium.
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You can also look up the next smallest noble gas
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and shorten it by just referring to its electron configuration as the base
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because those shells are full and don't change for any bigger elements.
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This is also how you can figure out the valence electrons for transition metals.
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Just look up their electron configuration, ignore the full shells of the next smallest noble gas, and the remaining electrons are the valence electrons.
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Easy peasy.
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Anyways, all this knowledge is going to cost you one subscribe and a thumbs up, thank you very much.
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Your comment is my delight and I shall now guide you, fine person, to the exit where the next lesson is excitedly waiting for you.
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Vocabulaire et conseils d’expression pour cette leçon
Cette leçon d’expression orale s’appuie sur la vidéo « GENERAL CHEMISTRY explained in 19 Minutes ». Les mots qui reviennent le plus souvent : electron, reaction, element, energy, atom. Cette vidéo contient 64 phrases et 4064 mots à répéter en shadowing. La partie parlée dure 18:49. Le locuteur parle vite, environ 216 mots par minute : attendez-vous à des liaisons et à des sons réduits. Seuls 77 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.
Vocabulaire clé de cette vidéo
15 mots de la vidéo à retenir, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| atom nom | /ˈætəm/ | atome |
| molecule nom | /ˈmɑ.lɪ.kjul/ | molécule |
| electron nom | /ɪˈlɛk.tɹɑn/ | électron |
| shell nom | /ʃɛl/ | coquille, coquillage |
| hydrogen nom | /ˈhaɪdɹəd͡ʒ(ə)n/ | hydrogène |
| element nom | /ˈɛləmənt/ | élément |
| particle nom | /ˈpɑɹtək(ə)l/ | particule |
| ion nom | /ˈaɪ.ɑn/ | ion |
| sodium nom | /ˈsəʊ.di.əm/ | sodium |
| acid nom | /ˈæsɪd/ | acide |
| oxygen nom | /ˈɑksɪd͡ʒən/ | oxygène |
| substance nom | /ˈsʌbstəns/ | substance |
| quantum nom | /ˈkwɑntəm/ | quantité |
| periodic adjectif | /ˌpɪɹiˈɑdɪk/ | périodique |
| orbital adjectif | /ɔɹ.bət.l̩/ | orbital |
Les verbes à particule que vous entendrez
| Mot | Prononciation | Sens |
|---|---|---|
| fill up verbe | remplir | |
| fall apart verbe | tomber en morceaux | |
| fall back verbe | se replier, se rabattre | |
| figure out verbe | cerner | |
| give away verbe | offrir, donner | |
| give off verbe | /ɡɪv ɒf/ | émettre |
| put together verbe | assembler | |
| throw away verbe | rejeter, jeter |
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| Phrases conditionnelles if + proposition, will/would + verbe — une condition et son résultat | if you give it enough energy, it will · If it's below zero, the water will spontaneously |
| Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait | is made · are called · is listed |
| Propositions relatives who / which + proposition — une précision sur une personne ou une chose | core, which is · mass, which is · metals, which are |
Prononciation à surveiller
Le locuteur utilise 28 contractions et formes réduites, comme don't, they're, doesn't. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « th »: thumb /ˈθʌm/, endothermic /ˌɛndəʊˈθəːmɪk/, enthalpy /ˈɛn.θəl.piː/
- Les sons « sh » et « zh »: shell /ʃɛl/, concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, equation /ɪˈkweɪ.ʒən/, configuration /kənˌfɪɡ.əˈɹeɪ̯.ʃən/, transition /tɹænˈzɪʃ.ən/
- Mots longs — placez bien l’accent: periodic /ˌpɪɹiˈɑdɪk/, concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, configuration /kənˌfɪɡ.əˈɹeɪ̯.ʃən/, spontaneous /spɑnˈteɪ.ni.əs/, equilibrium /ɛkwɪˈlɪbɹɪəm/
Les sons difficiles pour les francophones :
- /h/ — il se souffle, il n’est pas muet: hydrogen /ˈhaɪdɹəd͡ʒ(ə)n/, whereas /(h)wɛɹˈæz/, hammer /ˈhæmɚ/, behave /bɪˈheɪv/, hydronium /haɪˈdɹoʊ.ni.əm/
- /tʃ/ et /dʒ/ — à ne pas adoucir en « ch » et « j »: hydrogen /ˈhaɪdɹəd͡ʒ(ə)n/, oxygen /ˈɑksɪd͡ʒən/, mixture /ˈmɪkst͡ʃɚ/, naturally /ˈnæt͡ʃ.(ə.)ɹə.li/, voltage /ˈvəʊltɪd͡ʒ/
- /r/ anglais — langue recourbée, sans frotter la gorge: electron /ɪˈlɛk.tɹɑn/, hydrogen /ˈhaɪdɹəd͡ʒ(ə)n/, particle /ˈpɑɹtək(ə)l/, periodic /ˌpɪɹiˈɑdɪk/, orbital /ɔɹ.bət.l̩/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme atom, molecule, electron.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.