So when it comes to atomic size or atomic radius, recall that when we go from left to right, it's going to decrease. So it decreases going from left to right. And it's going to increase going down a group for transition metals were moving across a period. The size for the most part remains constant. That's because as you're moving across the period you're staying within the same shell. Okay, so you're staying relatively the same size, You're just adding electrons. So here if we're heading towards the top right corner, we can say that the overall trend. Is that atomic radius is decreasing. Now here we're gonna say moving when moving from the 3D transition metals to the transition metals, we see an increase an atomic radius. So we're looking at the periodic table, remember that starting here, this would be three deep. So this is our 3D row, This would be 40. And then here this would be five D. Now remember the ones that are blocked out here? They're man made for the most part many of them are so they're kind of unpredictable in the way they behave. So we don't even worry about looking at them. So we say that the atomic radius increases as we go from three D to to 40. And we can see that we can see 1 62 to 1 80. We can see 1 27 to 1 36. But then when we're moving from 40 to five D, the pattern is quite different and stays relatively constant. So if we go from Tekken Iem to Ari here, the numbers are pretty close 1 34 to 1 35 1 34 to 1 36. 1 44 - 1 44. So we're going down a group but the atomic radius isn't getting bigger. So why exactly is this occurring? Well, we're gonna say this phenomenon referred to as the land denied contraction. Remember your land tonight's start here And they lead to that row of elements that were not showing here, that's 14 of them. What's occurring here, Why? They're the size thing relatively the same is because you're incorporating the f electrons. So we're incorporating our f electrons um within this atom. And if you're incorporating the f electrons, but your shell stays the same size, you also need to anticipate that your you have to incorporate protons as well for all those electrons are incorporating that R F electrons, you also have to incorporate more protons that come with them. Those protons are gonna jam themselves more into the nucleus. And what's going to occur since you're not expanding in size because you're staying in the same row, you're gonna have the electrons becoming more attracted to the nucleus. Remember the attraction for the nucleus and the electrons that's our effective nuclear charge as a result of the electrons becoming more attractive to the more positively charged nucleus, they're going to move in closer. This is going to cause a slight contraction of your atom and this is why you're not going to see a large increase or a substantial enough increase in your atomic radius as you go from the four D 25 D. Um row. Okay, so this is known as the land tonight contraction, and it's a consequence of adding more electrons that are from f orbital's coming along with those electrons or additional protons, which causes a greater traction for the electrons to the nucleus, which causes a contraction of the atom.