Now that we'veclassified our facets into groups on theperiodic table, let's see just how to recognize thenumber that valence electrons. And so because that thisvideo, we're just talking about thevalence electrons for aspects in the key groups. As soon as we speak aboutthe main groups, you're using the onethrough eight device for classifying groups. For this reason one, two, three, four,five, six, seven, and eight. Therefore we're going to neglect theother means to number the groups. And so therefore, we're walking toignore teams three v 12 for this video. And so if we're talkingabout the main groups, the valence electronsare the electrons in the outermost shell orthe outermost energy level. And so let's see ifwe can figure out how numerous valenceelectrons salt has. So because that sodium, if I wanted towrite an electron construction for sodium-- Iassume you currently know how to do these-- for this reason youwould speak it is 1S2, 2S2, 2P6. And that takes friend allthe means over here to neon. And also then that bringsyou to the third period or the third energy level. And you have one moreelectron to issue about. And so that electron wouldgo into a 3S orbital. For this reason the complete electronconfiguration is 1S2, 2S2, 2P6, and 3S1. As soon as I desire to number outhow numerous valence electrons sodium has, the numberof valence electrons would be same to thenumber of electron in the outermost shell,the outermost energy level. Because that sodium, sodium has the firstenergy level, second energy level, and thethird energy level. The outermostenergy level would, of course, thethird power level. Therefore if i see exactly how manyelectrons sodium has in that is outermost power level,it's only one this time. So that way that sodiumhas one valence electron. And that's veryconvenient, due to the fact that sodium is found in team one. And so we have the right to saythat for key groups, if you want to figure outhow many valence electron you have, it's just equalto the group number. For this reason the team numberis same to the number of valence electrons. And also so the makeseverything yes, really easy. And so if I want to representa neutral atom of sodium through its one valence electron,I could draw salt here, and also I could draw one valenceelectron alongside sodium like that. Every right. Let's go ahead and writethe electron configuration for chlorine next. Therefore here's chlorine over here. And also so if I want to writethe electron configuration for chlorine, it would certainly be1s2, 2s2, 2p6, and once again, the takes me allthe means to neon. And also so now, I'm overhere in the third energy level, or the 3rd period. I have the right to see that i wouldfill 3s2-- therefore 3s3. And also that put meinto my ns orbitals. For this reason how numerous electronsare in my ns orbitals? One, two, three, four, five-- soI'm in the third energy level, I'm in ns orbitals, andI have 5 electrons. And so that would certainly be theelectron construction for chlorine. If I desire to number out exactly how manyvalence electrons chlorine has, I need to look for the electronsin the outermost shell, or the outermost energy level. So i have, when again, the firstenergy level, the 2nd energy level, and also thethird power level. So I want the totalnumber of electron in the outermost power level. Therefore how many electrons arein the 3rd energy level? Well, there's 2 andfive, because that a full of seven. For this reason chlorine has actually sevenvalence electrons. And also once again, that'svery convenient, since chlorineis in team seven. And also so let's walk aheadand attract chlorine with its sevenvalence electrons. So here is chlorine. Therefore one, two, three, four, five,six, and seven, like that-- and also so the factor Ipicked sodium and also chlorine is, of course, due to the fact that thesodium and also chlorine will react together to formsodium chloride. And also let's analysis whathappens making use of our electron configurations. And so salt is goingto lose one electron. For this reason a neutral atom ofsodium has actually equal number of protons and electrons. Yet if salt loses itsone valence electron-- so it's going come loseits one valence electron, and also I can display itsone valence electron, actually, is moving overhere come the chlorine. Therefore now, as soon as Idraw sodium, I need to represent it asan ion, a cation. Sodium used to haveequal number of protons and electrons, but itjust shed one electron. Therefore, it's left v anunbalanced number of protons. So it has actually one moreproton than electrons. So it's a add to one charge. Therefore Na+ is the sodium cation. The sodium cation is stable. And the reason why needs to dowith the resulting electron configuration. For this reason if i look in ~ the resultingelectron configuration-- allow me walk ahead anduse yellow here-- it would be 1s2, 2s2, 2p6. And also so the electronconfiguration because that the sodiumcation is the same as neon, i m sorry is a noble gas. And also we know that noble gasesare typically unreactive, and also that has to do v thefact that their electron configurations are full intheir outermost power level. So the salt cation is stable,because it has actually an electron construction likethat that a noble gas. So because that chlorine, if us thinkabout exactly how chlorine reacts, chlorine has sevenvalence electrons. And also let's discover it onour regular table here. So here is chlorine. Chlorine has actually sevenvalence electrons. If chlorine gets onemore, climate chlorine would have an electronconfiguration prefer a noble gas, favor that the argon. Therefore chlorine will certainly gainan electron here. So let's walk ahead and also writethe brand-new electron configuration. If a neutral atom that chlorinepicks up an electron, well, the electronwould include right in here. So rather of 3p5,we would write 3P6. And so the electronconfiguration for the chloride anion wouldbe 1s2, 2s2, 2p6, 3s2, 3p6. Let me just go ahead andhighlight that-- 1s2, 2s2, 2p6, 3s2 and then 3p6. Let's walk ahead and draw it. For this reason we're no much longer talking abouta neutral chlorine atom here. We're talking abouta chloride anion the picked up one electron. Therefore it take it thatelectron indigenous sodium. For this reason I'm going come showthat electron in red-- has actually moved over here tochlorine, choose that. And so chlorinegains one electron. For this reason it used to beoverall neutral. It supplied to have an equalnumber of confident charges and an unfavorable charges. But it simply addedone more electron. So that offers chlorinea an adverse charge. Therefore it's currently the chloride anion. And so you have ananionic bond the forms in between the sodium cationand the chloride anion here. So the attraction ofthese opposite charges creates an ionic bond. And also so this is one exampleof a group one alkali steel reacting with a halogen. For this reason in our video onthe routine table, us talked about elements. Us talked around thesebeing our alkali metals. And also since these alkalimetals room all in group one, lock all have onevalence electron. And we talked aboutour halogens over below as likewise beingextremely reactive. And also the reason theyare so reactive is if castle addone an ext electron, they have actually the electronconfiguration that a noble gas. And also so drawing theelectron configurations, thinking about valenceelectrons and also thinking about the resultingelectron configurations allows you to figure outhow these points react. And also so that is thereason why we deserve to say that team onemetals are so reactive, and why we have the right to say thatgroup seven halogens, or 17, space so reactive. It's therefore conceptof electron configurations and also drawing out yourvalence electrons. And also so we might figure outhow countless valence electrons something rather has, right? for this reason let's say us wereasked to figure out how countless valenceelectrons oxygen has. So all us would must dois look at the group number, right? therefore this would be--oxygen is in team six. And so therefore, oxygenhas 6 valence electrons.
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And also so if girlfriend wantedto stand for oxygen through its six valenceelectrons, you can go ahead and draw in sixvalence electrons favor that. And also so it's a an extremely useful thingto think around that if you desire to discover the numberof valence electrons, think around the team numberfor main team elements.