 Let's see what's the trend of metallic nature in our periodic table. Basically, how does the metallic nature vary as we go across a period and down a group? And if you're wondering what's metallic nature, then I hope you recall that a metal is an element that can easily give away its outermost electron. For example, sodium is a very good metal. It has one electron in its valence shell and it will participate in chemical reactions to give that away. Because by doing so, it can attain a complete octet, just like the noble gas, the nearest noble gas, neon, and therefore it will become more stable. So metals like to give away their valence electrons and become more stable. So if there is an element that can easily give away its outermost electron, then it is going to be more metallic in nature. Whereas, if there is another element that requires some effort to give away its outermost electron, then it's going to be less metallic in nature. So that's the trend that we are looking for. But before we begin, let's try to find out what makes it easier or hard to give away this outermost electron. Well, actually, you will recall that the electrons are held in their position because of the pulling force by the nucleus. See, nucleus has positively charged protons and they will attract the negatively charged electrons, right? Opposite charges attract each other. So because of this pulling force, the electrons are held in their position. So if this pulling force is more, then it will be hard to give away this electron. But if this pulling force is less, then it will be easier to give away this electron and the element will be a better metal. Well, then what does this pulling force depend on? Well, it depends on two things. First, the effective nuclear charge and second, the distance from the nucleus. Now let's understand each of these factors in little detail. So the first one is effective nuclear charge. This basically means, effectively, how many protons are pulling our electron? If the number of protons pulling is more, then the pulling force is going to be higher. If the number of protons pulling is less, then the pulling force is going to be lower. For example, you know, if you have one magnet pulling an iron nail, the pulling force is less compared to if you had two magnets, right? What about this term effective? What does this mean? So let's understand this. Let me draw the valence electrons somewhere below over here. Now imagine that this is being pulled by the protons over here. There are 11 protons in the nucleus of sodium atom. So there will be, the pulling force will be due to 11 protons. But is that it? No. See, there are some electrons in between and these electrons will be repelling our valence electron. See, these electrons are negatively charged just like our valence electrons and like charges, they repel each other. So there are 10 electrons inside. They will be repelling our valence electrons. So our valence electron will be feeling a repulsive force by 10 electrons. Okay. So, so it's experiencing a pull by 11 protons and a repulsion by 10 electrons. So we can say that effectively this electron is being pulled by one proton. Right. Let me actually replace this. Effectively, I can say that 11 minus 10 is one. This electron is experiencing a pull by one proton. So this becomes its effective nuclear charge, the effective nuclear charge that this electron experiences. Well, in reality, these calculations are going to be slightly complicated, which we will be talking about in future videos. But for the sake of this video, this level of simplicity is okay. Fine. Now let's talk about the distance from the nucleus. You see, if the electron is closer to the nucleus, then the force that will experience is going to be stronger, whereas if this electron is farther away, then the force is going to be slightly weaker. For example, if we take the analogy of magnets again, so if this magnet, if I take this magnet a little farther away, you can imagine that the pulling force that it will experience will suddenly reduce. So the force also depends on the distance from the magnet, right? So the pulling force that this electron experiences, it depends on how closer or how farther away from the nucleus this electron is, okay? And you know what? The distance from the nucleus is somewhat related to the number of shells, the number of shell in which the electron is. So generally speaking, in general, if this electron is in a higher shell, that means it will be farther away from the nucleus. Currently, this electron is in the third shell. If this electron were in the fifth shell, it would have been farther away from the nucleus. Generally speaking, now let's see how the metallic nature varies as we go across a period. So the two factors that decide this are one, the effective nuclear charge and two, the distance from the nucleus. Now let's focus on the period number two, the elements of period number two. Let me bring these elements closer. Well, let's not talk about neon for now, because we know that neon is a noble gas. It's not going to lose electrons. So what's the point of talking about it? Let me hide this. Okay, now first let's see how the effective nuclear charge varies as we go across this period. So first of all, let's talk about lithium. So lithium's atomic number is three. It has got three protons in the nucleus and three electrons. If we focus on this valence electron, it is being pulled by three protons. But that's not it. It's being pushed by, repelled by these two inner electrons also, like charges repel. So this electron is being pulled by three, being repelled by two. So technically speaking, this electron is being pulled by one proton effectively, right? So it's effective nuclear charge. The effective nuclear charge that this electron experiences is going to be one. Now let's talk about beryllium. So beryllium's atomic number is four. It has four protons at its nucleus and four electrons. If we focus on this valence electron, okay? So this is being pulled by these four protons and it's being repelled by these two inner electrons. Well, this electron is in the same shell as this valence electron. So this will also provide some repulsion. But you know what? Electrons in the same shell, they provide very little repulsion. So to keep calculations simpler, I'm going to ignore this, okay? So this electron is being pulled by four and is being repelled by these two. So effectively speaking, this electron is being pulled by four minus two is two, two protons. So it's effective nuclear charge is going to be two. Now let's talk about boron, the next element. Boron's atomic number is five. It will have five protons and five electrons. Now can you pause the video and tell me what will be the effective nuclear charge experienced by this electron? Pause and try. Now if you have tried it, let's see. So see this electron is being pulled by these five protons and being repelled by these two inner electrons. See these two electrons will also be repelling, but only a little bit. They are in the same shell, right? So for simpler calculation at this level, let's ignore them. So this electron is being pulled by five, repelled by two, five minus two. Effectively, we can say that it's being pulled by three. So it's effective nuclear charge is going to be three. Now as you can see, the effective nuclear charge is increasing as we go across a period. Now that would mean that as we go across the pull on the valence electron, that increases. This atom will have a higher pull on the valence electron than this one, than this one. Now that would mean that this atom finds it harder to lose this electron than this, than this. Now that would mean that this atom is less metallic than this one, than this one, okay? So as we go across a period, the effective nuclear charge, it increases. And because of this, the metallic character, this decreases. Now let's talk about the effect of distance from the nucleus. So in the video of atomic radius, we have already seen that the atomic radius reduces as we go across a period. And that's also happening because the nuclear charge is increasing. And with increasing nuclear charge, it is able to pull the shells much more closer, okay? Now if the distance between the nucleus and the valence electron is decreasing, then that would mean that the pull between them has increased. Now if the pull has increased, it becomes harder and harder to give away the valence electron. That means the metallic character has reduced. So what we see is that as we go across a period, the distance between the valence electron and the nucleus is reducing. Because of which the metallic character is again reducing, okay? So because of both of these variables, the metallic character reduces. So therefore we can say conclusively that as we go across a period, the metallic character reduces. Now let's see what happens as we go down a group. So here I have elements of group number one. Over here, I haven't shown hydrogen because technically, hydrogen does not belong to group number one. And we have spoken about why in the video of modern periodic table. So go ahead and watch that first. Over here, let's first see how the distance between the nucleus and the valence electron varies as we go down a group. We'll come back to effective nuclear charge a little later. So for this, I have drawn the electronic configuration of lithium, sodium and potassium, the first three elements of this group. And from the video of atomic radius, you might recall that the atomic radius increases as we go down a group. Well, you can see over here, there are more shells. There are newer shells getting added between the valence electron and the nucleus. So therefore the atomic radius, the distance between them increases. Now with this, we can say that the pull or the attraction that the valence electron feels is going to reduce. We saw that with the help of magnets also. If two magnets are getting far away, then the attraction, the pull between them is reducing. The same thing will happen over here. Now that would mean that it will become very easy for potassium to give away its electron compared to sodium compared to lithium. So that means as we go down a group, it becomes easier to give away the valence electron. That means the metallic character is increasing as we go down. So therefore in summary, we would say that as we go down a group, the distance between the valence electron and the nucleus increases. And therefore the metallic character also increases. Now let's talk about the effective nuclear charge. So lithium has an atomic number of three. That means it has three protons. So this valence electron is experiencing a pull by three protons. But it's also being repelled by these two electrons. So three are pulling it and two are repelling it. So effectively speaking, three minus two, one. This electron experiences a nuclear charge of one. So its effective nuclear charge will be one. Now let's talk about sodium. So sodium's atomic number is 11. That means it has 11 protons. Now this valence electron will be pulled by 11 protons. But it's also being repelled by two plus eight, 10 electrons. So being pulled by 11, being repelled by 10. So 11 minus 10 is one. So effectively speaking, this electron is also being pulled by one proton. It's effective nuclear charge is one. Similarly, if you look at potassium, its atomic number is 19. It has 19 protons. This valence electron will be pulled by 19. But it'll be repelled by two plus eight, 10 plus eight, 18. Pulled by 19, repelled by 18. 19 minus 18 is one. So effective nuclear charge for this electron is going to be one. Now if you notice over here, the effective nuclear charge remains the same as we go down. Now this means that metallic character should not change. Well, that's not actually true. See, calculating effective nuclear charge is not that straightforward. And we will look at how to calculate effective nuclear charge in future videos. But for now, I looked upon Wikipedia and turns out this is how the effective nuclear charge varies. It increases actually as we go down a group. Now you would say that this means that our valence electron of potassium, this will experience a higher effective nuclear charge. Means a more stronger pull than the previous atom, right? Now this would mean that it would be harder to give away this electron. Therefore potassium should be less metallic than sodium. And sodium should be less metallic than lithium, right? So basically the effective nuclear charge should actually is actually increasing as we go down a group. And because of this, the metallic character should reduce. Now there is a problem. Should the metallic character decrease or increase? Well, see, it turns out that the change in effective nuclear charge, this is very small as we go down. So therefore due to it, the decrease in metallic character is small compared to the distance. The distance increases by a lot as we go down. And therefore the increase in metallic character should be more. So if you see net net as we go down a group, the metallic character will be increasing, okay? Now let's summarize the video. In this video, we spoke about the periodic trend of metallic character. And metallic character can be measured by the ability of an element to give away its electron. Now this depends on two variables, the effective nuclear charge and the distance between the nucleus and the valence electron. Now as we go across a period, the effective nuclear charge increases, meaning it becomes harder to give away the valence electron. Also the distance reduces, meaning it becomes even more hard to give away the valence electron. So as we go across a period, it becomes harder to give away the electron, meaning the metallic character reduces. Now as we go down a group, and this is where you need to be careful. As we go down, the effective nuclear charge increases. So it becomes harder to give away the electron. But the distance, this also increases, making it easier to give away the electron. So what happens? Well, it turns out the distance increases a lot. So it becomes much more easier to give away the electron. So therefore net net as we go down, it becomes easier to give away the electron and therefore the metallic character increases.