So Atomic radius is the distance between Adams nucleus and its outer electron shell, otherwise known as its valence shell. So here, if we take a look, we have our nucleus in the middle. And here we have our outer shell. The distance between the nucleus and the outer shell is our atomic radius. R. Now remember, within the nucleus we have our protons and neutrons are protons are positively charged particles. Neutrons are neutral and the nucleus itself contains our proton and our neutron. Now we're gonna say, here, going down a group, we're going to say that the number of electrons increases because our shells get larger and larger and they can hold more and more electrons. And we're gonna say that the number of electron shells also increase. But we're going to say, moving across the period. Though we're going to say that the number of electrons with within the same shell also will increase. We're gonna say increasing the number of shell electrons in the same shell causes greater attraction with the nucleus. And what this does is it causes a slight decrease in our atomic radius. So we have these two forces at work. We're adding more electrons, and as a result our Adam gets larger and larger with more and more shelves. But as we add more and more shells, there's gonna be more electrons found within each of those shelves. This is going to cause some issues with our atomic radius, so there's an increase in a decrease type of phenomenon happening here with the increase of the number of electrons. The overall periodic trend is that as we move from left to right, so remember, we're always heading towards the top right corner of the periodic table. Are atomic radius will decrease? So click on to the next video and let's take a look at what this periodic table would look look like in terms of atomic radius.
as I stated before, as a move from left to right across a period and as we move up a group are atomic radius will decrease here. I've reimagined the periodic table to show how the atomic radius changes as I move across it Here, we have hydrogen and its average atomic radius is km. And we can see as we go from hydrogen to helium, the number drops. If we go to road to we have lithium, which is 152 p km. And as we go from left to right, we can also see for the most part the atomic radius will decrease. Now of course with chemistry, there are exceptions. A lot of these exceptions happen with the transition metal, we're gonna say the erase the electron arrangement for transition metals makes their patterns less predictable. So we just don't include them. Now you don't have to memorize these numbers at all for each of the elements. All you need to remember is the general trend. And the general trend is, as we head towards the top right corner of the periodic table, we expect the atomic radius overall to decrease. So just keep that in mind when you're looking at atomic radius.
Moving towards the top right corner of the Periodic Table causes the atomic radii to decrease.
3
example
Periodic Trend: Atomic Radius (Simplified) Example 1
Video duration:
1m
Play a video:
here for this example. It says which of the following atoms has the largest atomic radius. So we have potassium rubidium Gayatri. Um Now remember we said that the transition metals are hard to predict. So we can ignore this one, calcium and strontium. All right. So I've highlighted the four that we're looking at. And remember we have the numbers here. So it's a little bit of cheating. But what's the general trend? As we start heading towards the top right quarter, we get larger and we get smaller in terms of the atomic radius. We get smaller in terms of atomic radius as we head towards the top right. But you're not looking for the smallest atomic radius. We're looking for the largest. So it's the opposite trend of that. Well, as we head towards the bottom left, we expect our atomic radius to get bigger. So of course we have the numbers here. But remembering the general trends if you don't have the numbers is important. And we know that rubidium is most to the left, and it's for this down. So that's why it has the highest atomic radius out of the four. So here, this would meet, make option B the correct choice.
4
Problem
Problem
Which alkaline earth metal has the smallest atomic radius?
A
Ca
B
Rb
C
Na
D
Ra
E
Fr
5
Problem
Problem
Which alkaline earth metal has the largest atomic radius?
A
Na
B
Ba
C
Cl
D
Mg
E
Li
6
Problem
Problem
Arrange the following atoms in order of decreasing atomic radius:Sr, Se, Ne, Ga
