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Solar system

Hi. I’m back at Lakeside School”,and I’m in the chemistry lab as you can see.Now, look around youand try and count how many differentsorts of materials you can see.Ten? Easily.A hundred? Not too hard.And if you countedreally carefully, well, look at all these materials here.You could probably come up quite easily to a thousand”,10″,000, or maybe even 100″,000.That’s because in a Universe with a hundred elements”,you haven’t just got a hundred different materials.Those elements can combine with each otherin a huge number of different waysto form millions and millions of new materials”,all the materials we see in the world around us.All these new materials eventually combine to find…to create entirely new astronomical bodies.The most important by far for us, of course”,is our home planet, the Earth.But before we describehow the Earth and the other planetsof the solar system was created”,there’s a little problem we have to take up.You remember from the last unit”,we saw that all those new elements that were createdmade up only two percentof all the atoms in the Universe.Yet, if we look at our earth, we’ll find that 90% of the earthis made up of elements like iron, oxygen, silicon”,magnesium, and other elements createdin supernova and dying stars.So, how did they get concentrated like thisto form planets and bodies like that?Now, before I give my answer, I’d like to askif you have any ideas about how that might have happened.To answer these questions we must think about chemistry.And chemistry is all about how different elements link up”,how the atoms link up to form what we call molecules.How atoms link up depends very muchon the arrangement of their electrons.Some elements such as helium are very, very stable”,they hardly ever link up with other atoms.In fact, they’re known as the noble gases.It’s as if they’re too snootyto join up with all the other atoms.You’ll find them on the right sideof the periodic table by the way.But most atoms really like to link up with other atoms.We say they’re reactive.Hydrogen and oxygen, for example”,are always looking for chances to link up with other atoms.If you see burningor you see a flame, what you’re really seeingis oxygen linking up really violentlywith other atoms, it’s very reactive indeed.Now, when atoms join together, we call them molecules.Each molecule has its own distinctive qualities”,which may be very differentfrom the elements of which they’re formed.For example, hydrogen and oxygenare both gases, but when they combine”,they form a very, very familiar liquid– water, H2O.And water has qualities completely differentfrom both hydrogen and oxygen.Different types of moleculesalso have different types of bonds.Some bonds are extremely rigid, flex…but others are very flexible.Some are very strong, very hard to break”,others are very easy to break.So there’s a huge varietyof different types of links between molecules.Carbon, for example, can link up with itselfto form diamonds.Now, in a diamondthe bonds are extremely strong and extremely rigid”,so a diamond is very tough indeed.But carbon atoms could also link up with themselvesto form a very different material, graphite.Now, graphite is the led in a pencil.It’s very soft stuff indeed.So, different bonds make a lot of… lot of difference.Now, these different types of links”,different types of bonds mean we have a huge varietyof different types of materials.That’s what explains the huge variety of these materials.But note that it’s mostly elementsother than hydrogen or helium that make up these chemicals”,and that’s one reason why when we talk about rich chemistry”,we’re talking mostly about that tiny two percent of elementsfrom the periodic table.Atoms began to form molecules even in deep space”,in the… in the clouds of matterejected by supernovae and dying stars.How do we know this?Well, using spectroscopes, we can tell what elementsand what chemicals are out there.And we know there’s water, plenty of ice”,carbon dioxide, ammonia, acetic acid”,a whole range of simple moleculesthat are very familiar in daily life.There are also lots of silicates.Silicates are molecules made from silicon and oxygen”,and they make up most of the rocksin the earth’s crust.Now, in space, these molecules”,which were pretty simple by the way”,they included 10 to 20 atoms, at most 60.In space these moleculescouldn’t do a huge amount of interesting stuff”,but around newly born stars, it turns out you could doa huge amount of interesting stuff with these molecules.In fact, you could make planets.To see how this works, what we’re going to dois we’re going to travel back in time 4.5 billion years”,and we’re gonna zoom in.We’ve been looking at the Universe so far in this course.We’re gonna zoom in on one ratheraverage galaxy, the Milky Way.We’re gonna zoom in on one tiny part of it”,and we’re gonna lookat the birth of our solar system.Now, our sun formed like any other star”,from the collapse of a cloud of matterunder the pressure of gravity.That collapse like many others was probably triggeredby a huge supernova explosionsomewhere in our region of the Milky Way”,and that supernova explosion also seededthis cloud with lots of new materialsfrom other supernovae and from dying stars.As the cloud collapsed, it began to spin”,like a spinning pizza dough.And as it spun”,it slowly flattened out to form a disk.Now, this is something that happensthroughout the Universe”,which is why the Universe is full of flat disksfrom the Milky Way itself to our solar system”,even to the rings around Saturn.Astronomers call this sort of disk a protoplanetary disk”,or a proplyd.Now, as the proplyd that eventually formedour solar system began to collapse”,at its center, it got hotter and hotter and hotter”,until eventually fusion began and our sun was born.About 99% of all the material in the proplydwent into the sun– 99.9% in fact..That leaves 0.1% for the rest of the solar system.All that stuff was orbiting around the sunand, amazingly, that tiny residueis what formed all the rest of the solar system.Now, let’s begin by looking at the outer gassy planetsand how they were formed.The intense heat of the

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