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Silicon-based life | Properties of carbon | Biology | Khan Academy

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We've already spent a lot of time thinking about how awesome carbon is for life that really life as we know it is carbon-based in this all comes out of carbons ability to bond with other carbons inform all sorts of neat structures bonds with oxygen hydrogen and other things it back we have a whole class I molecules called organic molecules the just are molecules that involve carbon and carbons bonding capabilities really come out with electron structure we talked about this in the previous video but if we think about carbon it has a6 proton to the neutral carbon will have six electrons to love them are sitting at innermost shell and then the other four on it outermost shell on those for the ones that tend to react and we call them the valence electrons and so these villains electrons tend to form four coleville in bonds for example it you wanted a bond with four hydrogens well each hydrogen would contribute each hydrogen would contribute an electron to one of these pairs which urs and you're going to be a co v load bond and then the hydrogens the hydrogens can't feel that their outer shell is complete because hundreds is trying to get to to fill its outer shell to try to be a little bit more like helium and carbon is trying to get to 8 in its outer shell to be a little bit more like to meet me on neon has to dinner shell eat in it outer shell you might remember the octet rule that that that that with that Adams tried to get to eat or pretend like they have a lil eight electrons in the outer shell to feel stable and hear carbon is sharing eight electrons it contributed four and in the 400 and contribute for and it forms it forms methane now those have you were quite astute my dad said okay we know what I i know i other elements that tend to form for covalent bonds that have or valence electrons and in particular there's one that's awfully close to carbon on the periodic table and that's right over here this is this is silicon silicon has 14 protons in a neutral silicon would have 14 electrons it so let me draw that so if we have silicon right over your arms go focus on the electrons you would have to electron sitting in its innermost its innermost shell so and they're jumping round years not they're not these need well-defined orbits they're just dropping around a bit in that in that lowest energy in that in that in the innermost shell then you have another 8 its second shell to another strong 3 for 56 surveyed a tall jumping around all jumping around the second shell as the total fourteenth we are used up tents is going to have four and its outermost shell so one to you the tree for and these more in its outermost shell these are the ones that tend to do the reaction the reacting we call the Baylands electrons so if we want to destroy the village electrons we could do silicon has 4 valence electrons for as 41 to you 3 4 valence electrons just like carbon has a different number of electrons this for real electrons are actually one shell further out but as for the tender reacted it does tend to form for covalent bonds you might be say we won't can't we have life that is dependent that a silicon-based as opposed to carbon-based and if you thought that you would not be the first person to think about that science fiction or authors have have have your eyes then this right actually this is the this is a a screenshot from the devil in the dark episode 1967 from the original Star Trek where they said maybe they encounter Kirk encounters that the enterprise encounters these creatures that are silicon base to their called hoarders and they have all sorts have interesting properties so there there's you know there's some folks like to think maybe maybe silicon would you want to look at the chemistry things start to break down a little bit for example one of the neat things about carbon is it readily forms bonds with other carbons in these bonds can actually be quite long you can form all sorts of these hydrocarbons in all sorts of other a carbon-carbon structures long chains of carbon C can do that with carbon but it turns out that silicon silicon bonds are not that strong in silicon is not going to form is not going to form really long chains so silicon not going to do that even if you look at the same a simple a simple molecule like methane there is there is a molecule called silly but this does not readily form it doesn't have the same characteristics so this is also not going to be as good as methane and even if you think about something like carbon dioxide which is carbon which is carbon bonded having two double bonds so this is carbon having two double bonds two oxygens to so one double bond 21 oxygen another double want another oxygen in we're used to thinking about carbon dioxide in our everyday life is the gas plants are using these two to to pics the into their structure to actually grow their dating the carbon out of their carbon fixation we are we exhaled as carbon dioxide it's essential to life and you might think well what about what about silicon oxide and so dioxide is actually a a fairly common molecule fairly common compound but it does not exist at a gas just a tad the temperatures that were normally that we normally associate with the life most a silicon dioxide is in the form of quartz in the ground so that is courts over there so when you look at the actual ways that that that that silicon forms bond it actually does not seem actually close to as good as car video thing like silicon when silicon bonds with oxygen at a much not only is it in the solid format at normal temperatures where we normally associate life but these are very very very strong bonds much stronger than the bonds that carbon is forming with watch they're so strong there make it hard for them to be manipulated with the types of chemical reactions that we're used to seeing inside love organism so you know it's it's funded your eyes about this and I'll be the last person to rule anything out I think the universe will continue to surprise us with with things that right now we cannot even imagine but based on the chemistry we know and based on life as we know it even though silicon can form these four coleville it bonds and does have four valence electrons it still Lord year is good at carbones as in in doing the types of processes that that we think are necessary for life

Video Details

Duration: 6 minutes and 33 seconds
Language: English
Genre: None
Views: 6
Posted by: jake.goldwasser on Nov 19, 2015

Could silicon play a role similar to carbon's in supporting life?
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