Understanding Periodic Trends in Chemistry

Hi everybody, my name is Andre and welcome back to Med School EU. Today we are going to be learning about the periodic trends. So what are periodic trends? Well, based on the last video that we talked about, we know that the periodic trends are the ones that are most common. table of elements is organized in a way that it groups similar elements together and not specifically similar elements in what they are but more specifically of elements that exhibit similar properties. Now, these elements that exhibit similar properties are going to be grouped in different parts of the periodic table. And since they're grouped this way, they are going to exhibit these characters and they will create trends. So we're going to take a look at these four major trends that we have on the periodic table, which include ionization energy, electron affinity, metallic character, and atomic radius, which will give you an idea of how the periodic table is specifically. structured. So let's take a look at each one of these individually. The first thing that we're going to take a look at is the atomic radius. Now this periodic trend simply measures the size of the atom and this is done through measuring the distance from the center of the nucleus of the atom to the most outer electron. So it would be measured with the distance from the very center of the atom in the nucleus all the way down to the most outer electron. here. So this most outer electron right there and that distance is the atomic radius. Now that quite clearly measures the size of the atom. So the further the distance between the most outer electron and the nucleus the bigger the atom. So let's take a look at the trend on the periodic table that exhibits this property. So this diagram puts the atomic radius into perspective by combining and showing every single thing that's going on here. We have the non-metals that would have tiny atomic radius, whereas the metals would have the large atomic radius. Now we're going to talk about why this is the case. I'm going to list some factors here, but the general trend, periodic trend of the atomic radius is going to be that it increases going towards the left and it increases going downwards. So why does it increase? What is the reason for that? The biggest factor... that would play a role here is nuclear charge and the reason for that is because when you have a higher number of protons meaning higher nuclear charge because as we can recall from previous lectures that the atomic number will resemble the number of protons and the number of electrons so we're going to be looking at the number of protons specific So what would make the electron, the most outer electron, be closest to the nucleus right here? Why would the electron be there instead of being super far away? Well, attraction. Positive attracts the negative. What's inside the nucleus? Positive protons. Now the more positive protons you have, the higher the attraction you have. So you're going to pull all of these electrons inward more because you simply have a high... number of positive charges inside the nucleus and as we can see that the nonmetals are going to have higher number of protons than the metals in most cases. So if you're trying to compare for example fluorine, fluorine has nine protons whereas beryllium has four protons. Now nine protons that is five more positive charges. It's going to attract the electrons. a lot more readily than beryllium would. Although beryllium has less of those electrons. So it's gonna keep them more loose. Whereas on fluorine, the electrons are gonna be very, very tightly close to the very positive nucleus. Now, as we expand downward, the increase is going to be caused by another shell forming. So more shells would equal to bigger size. At the same time, more... protons would equal to smaller size. So next let's talk about ionization energy and ionization energy could be defined as the amount of energy required to remove an electron from a neutral atom and there could be multiple ionization energies and sometimes you will see first ionization energy second ionization energy etc but what this really means is your second electron removed or third electron removed. Now the electrons that will be removed from the atom are obviously going to be on the valence shell. They will be on the very outer shell and the electrons that will be removed will be called valence. electrons and so why is that why are we not removing electrons that are close to the nucleus well the reason for that is because the ones that are close to the nucleus are very highly attracted to the nucleus so therefore it's hard to rip it out of there but if it's something that is floating really far away from the nucleus then it's a lot easier to grab and remove. So here I've got my sodium element and my chlorine element and as you can see here sodium has 11 electrons but because it only has 11 positive charges 11 protons in the nucleus it's going to keep this one further away so its atomic radius will be much bigger. than the chlorine. Although chlorine has 17 electrons, so it's going to be harder to keep them kind of together. But at the same time, the effect of 17 positive charges in the nucleus is going to be huge. So it's going to keep these electrons super, super tight to the nucleus. And good luck ripping this electron out of there because it's so close to the positive charges that it requires a lot of energy to remove. Therefore, it will require high ionization energy. in order to remove an electron from there. Whereas here, it will require low ionization energy to simply remove this electron from there and satisfy its octet rule. So this is a perfect explanation for atomic radius and ionization energy if you're trying to understand the two periodic trends. So going back to our ionization energy trend in the periodic table, we can safely say that it's going to increase as you... go further to the right and it's going to increase as you go upwards and the reason it increases as you go upwards is simply because you're going to have less shells and less shells meaning they're going to be closer to the nucleus and therefore it's going to be harder to remove that electron from its outer shell. The next periodic trend is electron affinity and that is the amount of energy released when electron is gained. by an atom. Now this periodic trend kind of goes hand-in-hand with the last one we discussed which was ionization energy because I often think of it although the definition is different I often think of electron affinity is how how likely is the atom to gain an electron and so obviously if it's hard to remove an electron from the atom it's also easy for that atom to gain an electron so therefore the amount of energy released by that atom will increase because it is a lot easier for them to gain it it doesn't require all that energy so the periodic trend will follow the same path simply because the the same trends are going to be applied and the same reasoning and the same factors will will apply so going again along with the octet rule in terms of gaining electrons well, the fluorine will gain an electron much, much easier than the sodium. And, of course, the elements that are going to be higher up on the periodic table will gain those electrons also easier because they have clear access to the nucleus. Whereas the electrons here, let's say bromine or iodine, they have 53 electrons in iodine. Now, 53 electrons, that's quite a lot. So, therefore, you're going to have lots of... shells and a big big big distance between the outer shell and the center of the atom. Now if you have that big distance the affinity the attraction is going to be a lot smaller than something like fluorine that only has two and they're very tightly compact together. So therefore this trend follows exactly the same pattern as the ionization energy. Now just to sum that up the most important factors are going to be nuclear charge Because if you have more protons, where you have more protons on the right side versus the left side, you are going to have higher electron affinity. Now the atomic size, so lower size of the atom, will have higher electron affinity. And of course the number of valence electrons is going to depend as well. So therefore octet rule will also play the same role. as it did in the last. periodic trend that we discussed. Now finally metallic character is quite a simple one to discuss because we already talked about how the periodic table is split into the staircase right here where this side is non-metals and this side are going to be metals and of course further you go to the side of the metals the higher the metallic character going to be but that's not particularly what metallic character stands for metallic character stands for the level of reactivity of a metal so if we're talking specifically about level of reactivity activity of a metal, well the non-metals are going to be out of the game here. So therefore we're going to be more specifically looking at the competition between the metals themselves. And the trend will follow further to the left and downward as the bigger the atom and also the less number of electrons in the outer shell. For example the ones here on the first group only have one electron in the outer shell. So therefore it's a lot easier for them to react with something like a fluorine or a chlorine which will just take away that one electron. Whereas it's a little bit harder for bromine or beryllium, magnesium, calcium to react because they have two electrons to give up. So they're not going to react as readily with something like chlorine or iodine for example. So that is exactly why the metallic character is so important. terms of its level of reactivity follows this particular trend. Now finally I wanted to discuss a little bit about ions. Ions are simply charged elements. Where did the charges come from? They come from losing or gaining electrons. So we're gonna see how the periodic table is structured and how each of these groups is going to lose or gain its electron and therefore what charge is it gonna is it gonna get. So for example This first group right here is going to have one electron in its outer shell. And in order to fulfill the octet rule, it's a lot easier to lose that one rather than gain seven. So therefore, when it loses one, it will be a plus one charge. Now, many of you might think, hey, it lost something. How can it be a plus one charge? Well, think of it this way. Let's talk about lithium, for example. Lithium has three electrons and three protons. So as an atom. it's going to be neutral three protons three electrons but think of it this way now that I lost that electron it's no longer three it now just becomes two and if it's two negative charges then overall charge is going to be one plus and this is exactly what happens for all of them here and the same principle applies to the rest so if we're talking about The second group has two electrons in the outer shell. Now, of course, energetically, it makes a lot more sense to lose two electrons rather than to gain two electrons. Now, these will be multivalent. And what that means is that iron could sometimes be 2+, or it could be 3+. So this depends on the type of iron that we're talking about and the type of ion we're talking about, which situation it faces. So we're not going to label these. specifically. But as we move further along to boron, for example, boron will be plus three. It will typically lose the three electrons rather than gaining five electrons because energetically that makes the most sense. Now carbon will either lose four or gain four. It's split in the middle because it has four outer electrons. Nitrogen has five electrons in the outer shell, so therefore it's very likely to gain three. Oxygen has six electrons. electrons in the outer shell so therefore it's likely to gain two rather than lose the six and fluorine being the most reactive and the most electronegative element is very very likely to gain one electron because it has seven in its outer shell and they're also very very close to the nucleus. Now these these ones right here noble gases will be zero as they have full octet already fulfilled. So these are the charges that you should memorize and you should know by heart. and understand how they are formed. This concludes our lecture for today. I encourage you to check out the next video about the chemical bond.

Hi everybody, my name is Andre and welcome back to Med School EU. Today we are going to be learning about the periodic trends. So what are periodic trends?

Well, based on the last video that we talked about, we know that the periodic trends are the ones that are most common. table of elements is organized in a way that it groups similar elements together and not specifically similar elements in what they are but more specifically of elements that exhibit similar properties. Now, these elements that exhibit similar properties are going to be grouped in different parts of the periodic table. And since they're grouped this way, they are going to exhibit these characters and they will create trends.

So we're going to take a look at these four major trends that we have on the periodic table, which include ionization energy, electron affinity, metallic character, and atomic radius, which will give you an idea of how the periodic table is specifically. structured. So let's take a look at each one of these individually. The first thing that we're going to take a look at is the atomic radius. Now this periodic trend simply measures the size of the atom and this is done through measuring the distance from the center of the nucleus of the atom to the most outer electron.

So it would be measured with the distance from the very center of the atom in the nucleus all the way down to the most outer electron. here. So this most outer electron right there and that distance is the atomic radius. Now that quite clearly measures the size of the atom.

So the further the distance between the most outer electron and the nucleus the bigger the atom. So let's take a look at the trend on the periodic table that exhibits this property. So this diagram puts the atomic radius into perspective by combining and showing every single thing that's going on here.

We have the non-metals that would have tiny atomic radius, whereas the metals would have the large atomic radius. Now we're going to talk about why this is the case. I'm going to list some factors here, but the general trend, periodic trend of the atomic radius is going to be that it increases going towards the left and it increases going downwards.

So why does it increase? What is the reason for that? The biggest factor...

that would play a role here is nuclear charge and the reason for that is because when you have a higher number of protons meaning higher nuclear charge because as we can recall from previous lectures that the atomic number will resemble the number of protons and the number of electrons so we're going to be looking at the number of protons specific So what would make the electron, the most outer electron, be closest to the nucleus right here? Why would the electron be there instead of being super far away? Well, attraction. Positive attracts the negative. What's inside the nucleus?

Positive protons. Now the more positive protons you have, the higher the attraction you have. So you're going to pull all of these electrons inward more because you simply have a high...

number of positive charges inside the nucleus and as we can see that the nonmetals are going to have higher number of protons than the metals in most cases. So if you're trying to compare for example fluorine, fluorine has nine protons whereas beryllium has four protons. Now nine protons that is five more positive charges. It's going to attract the electrons. a lot more readily than beryllium would.

Although beryllium has less of those electrons. So it's gonna keep them more loose. Whereas on fluorine, the electrons are gonna be very, very tightly close to the very positive nucleus. Now, as we expand downward, the increase is going to be caused by another shell forming.

So more shells would equal to bigger size. At the same time, more... protons would equal to smaller size.

So next let's talk about ionization energy and ionization energy could be defined as the amount of energy required to remove an electron from a neutral atom and there could be multiple ionization energies and sometimes you will see first ionization energy second ionization energy etc but what this really means is your second electron removed or third electron removed. Now the electrons that will be removed from the atom are obviously going to be on the valence shell. They will be on the very outer shell and the electrons that will be removed will be called valence.

electrons and so why is that why are we not removing electrons that are close to the nucleus well the reason for that is because the ones that are close to the nucleus are very highly attracted to the nucleus so therefore it's hard to rip it out of there but if it's something that is floating really far away from the nucleus then it's a lot easier to grab and remove. So here I've got my sodium element and my chlorine element and as you can see here sodium has 11 electrons but because it only has 11 positive charges 11 protons in the nucleus it's going to keep this one further away so its atomic radius will be much bigger. than the chlorine. Although chlorine has 17 electrons, so it's going to be harder to keep them kind of together. But at the same time, the effect of 17 positive charges in the nucleus is going to be huge.

So it's going to keep these electrons super, super tight to the nucleus. And good luck ripping this electron out of there because it's so close to the positive charges that it requires a lot of energy to remove. Therefore, it will require high ionization energy.

in order to remove an electron from there. Whereas here, it will require low ionization energy to simply remove this electron from there and satisfy its octet rule. So this is a perfect explanation for atomic radius and ionization energy if you're trying to understand the two periodic trends.

So going back to our ionization energy trend in the periodic table, we can safely say that it's going to increase as you... go further to the right and it's going to increase as you go upwards and the reason it increases as you go upwards is simply because you're going to have less shells and less shells meaning they're going to be closer to the nucleus and therefore it's going to be harder to remove that electron from its outer shell. The next periodic trend is electron affinity and that is the amount of energy released when electron is gained. by an atom.

Now this periodic trend kind of goes hand-in-hand with the last one we discussed which was ionization energy because I often think of it although the definition is different I often think of electron affinity is how how likely is the atom to gain an electron and so obviously if it's hard to remove an electron from the atom it's also easy for that atom to gain an electron so therefore the amount of energy released by that atom will increase because it is a lot easier for them to gain it it doesn't require all that energy so the periodic trend will follow the same path simply because the the same trends are going to be applied and the same reasoning and the same factors will will apply so going again along with the octet rule in terms of gaining electrons well, the fluorine will gain an electron much, much easier than the sodium. And, of course, the elements that are going to be higher up on the periodic table will gain those electrons also easier because they have clear access to the nucleus. Whereas the electrons here, let's say bromine or iodine, they have 53 electrons in iodine.

Now, 53 electrons, that's quite a lot. So, therefore, you're going to have lots of... shells and a big big big distance between the outer shell and the center of the atom.

Now if you have that big distance the affinity the attraction is going to be a lot smaller than something like fluorine that only has two and they're very tightly compact together. So therefore this trend follows exactly the same pattern as the ionization energy. Now just to sum that up the most important factors are going to be nuclear charge Because if you have more protons, where you have more protons on the right side versus the left side, you are going to have higher electron affinity. Now the atomic size, so lower size of the atom, will have higher electron affinity. And of course the number of valence electrons is going to depend as well.

So therefore octet rule will also play the same role. as it did in the last. periodic trend that we discussed.

Now finally metallic character is quite a simple one to discuss because we already talked about how the periodic table is split into the staircase right here where this side is non-metals and this side are going to be metals and of course further you go to the side of the metals the higher the metallic character going to be but that's not particularly what metallic character stands for metallic character stands for the level of reactivity of a metal so if we're talking specifically about level of reactivity activity of a metal, well the non-metals are going to be out of the game here. So therefore we're going to be more specifically looking at the competition between the metals themselves. And the trend will follow further to the left and downward as the bigger the atom and also the less number of electrons in the outer shell. For example the ones here on the first group only have one electron in the outer shell.

So therefore it's a lot easier for them to react with something like a fluorine or a chlorine which will just take away that one electron. Whereas it's a little bit harder for bromine or beryllium, magnesium, calcium to react because they have two electrons to give up. So they're not going to react as readily with something like chlorine or iodine for example.

So that is exactly why the metallic character is so important. terms of its level of reactivity follows this particular trend. Now finally I wanted to discuss a little bit about ions.

Ions are simply charged elements. Where did the charges come from? They come from losing or gaining electrons.

So we're gonna see how the periodic table is structured and how each of these groups is going to lose or gain its electron and therefore what charge is it gonna is it gonna get. So for example This first group right here is going to have one electron in its outer shell. And in order to fulfill the octet rule, it's a lot easier to lose that one rather than gain seven. So therefore, when it loses one, it will be a plus one charge.

Now, many of you might think, hey, it lost something. How can it be a plus one charge? Well, think of it this way. Let's talk about lithium, for example. Lithium has three electrons and three protons.

So as an atom. it's going to be neutral three protons three electrons but think of it this way now that I lost that electron it's no longer three it now just becomes two and if it's two negative charges then overall charge is going to be one plus and this is exactly what happens for all of them here and the same principle applies to the rest so if we're talking about The second group has two electrons in the outer shell. Now, of course, energetically, it makes a lot more sense to lose two electrons rather than to gain two electrons. Now, these will be multivalent. And what that means is that iron could sometimes be 2+, or it could be 3+.

So this depends on the type of iron that we're talking about and the type of ion we're talking about, which situation it faces. So we're not going to label these. specifically.

But as we move further along to boron, for example, boron will be plus three. It will typically lose the three electrons rather than gaining five electrons because energetically that makes the most sense. Now carbon will either lose four or gain four.

It's split in the middle because it has four outer electrons. Nitrogen has five electrons in the outer shell, so therefore it's very likely to gain three. Oxygen has six electrons.

electrons in the outer shell so therefore it's likely to gain two rather than lose the six and fluorine being the most reactive and the most electronegative element is very very likely to gain one electron because it has seven in its outer shell and they're also very very close to the nucleus. Now these these ones right here noble gases will be zero as they have full octet already fulfilled. So these are the charges that you should memorize and you should know by heart.

and understand how they are formed. This concludes our lecture for today. I encourage you to check out the next video about the chemical bond.

Transcript for:Understanding Periodic Trends in Chemistry

Transcript for:
Understanding Periodic Trends in Chemistry