Why does the shielding effect increase as you go down a group?

Answer 1

How does shielding effect alter atomic size? Glad you asked. We'll need to do just a bit of review so we can make sure we're on the same page, then we can answer your question. Grab a seat and let's kick it. You're familiar with the basic structure of the atom. Protons and neutrons are bound together in the nucleus (1H excepted), and the electrons form up around the nucleus in electron orbitals or electron shells. The protons in the nucleus are positively charged and they attract and "hold" the electrons, which are negatively charged, as best they can. You know the electrons don't like each other 'cause they're like charges and they repel each other, right? Sure. Let's look at that the idea that the positive charge on the nucleus collects the electrons and keeps them around, but the electrons have their own "game" to play. If we had a hydrogen atom with its proton and electron, and the electron was the size of an orange, the electron would be a couple of miles away. (That's ball park. Don't fire up your calculator.) Those quirky little electrons in an atom are a long way from the nucleus, relatively speaking. And there is a dynamic going on among the electrons. They form "shells" or assume orbits directly related to their Fermi energy levels, and those electrons have to work out some kind of agreement so they can avoid each other while being held onto by the nucleus. Does that make sense? Yeah, it does. Two things are happening at the same time. The nucleus is keeping the electrons "home" but the electrons have their own "club rules" that keep them away from each other. And this sets up the orbitals and the whole dealio with chemistry. Chemistry is all about atoms loaning out or borrowning electrons based on their nuclear charge and their electron structure. Let's look at that electron structure just a bit more closely. The electrons have formed up into shells and have specific Fermi energies to be where they are. But the outer electrons, those electrons in the so-called valence bands, are "vulnerable" to being loaned out if there aren't very many of them, and they set up a condition where they want to "get some friends" to join them if that valence band is only one or two electrons short of being "complete" or "full" or "inert-gas-like" in its structure. This, as we mentioned, is the entire setup for chemistry and the way atoms of given element will behave with their own kind or atoms of different kinds. As to the electrons shells, those orbitals are "areas of probability" as regards where electrons are "probably" going to be found. And the electrons in the orbitals that are closer to the nucleus put up a "curtain" or "veil" or "screen" between the nucleus and the outer electrons. These inner electrons actually act to "reduce the hold" the nucleus has on outer electrons. That's what electron screening is all about. Also, the inner electrons "push away" the outer electrons, and that's part of the dynamic. That's two things happening: nuclear attraction for the electrons, and the "get-away-from-me" actions of the electrons among themselves. The electrons form what is called the electron cloud, and this defines the volume the atom will take up. The valence shell electrons will be on the fringes of "electron society" and keep other atoms from getting closer than where they have taken up station in their orbits. What's the bottom line? That's your question. You know that the higher the atomic number of an element, the more electrons in the electron cloud. More electrons means more screening and more "stay-away-from-me" activity among the electrons, so heavier atoms might tend to be larger in diameter. But (and yes, there's always a but in there), that's only a generality. If we look at all the elements in a Group, which is a vertical column in the periodic chart, we see the size of the atom increasing as we go down the Group to the heavier elements. Pick any group and the atomic radius of the element increases going down the column. This is a clear indication of electron screening having an effect on the "closeness" of the outer electrons. Heavier elements within a given Group are larger in diameter. But if we take a horizontal line or row, the atoms get smaller as we move across to the right until we come to the inert gases. Then the size shoots way up. This it true 'til we get to Period 4 and the transition metals. Their sizes are all similar, but they don't "follow the rule" as regards getting smaller from left to right. This has to do with the positive charge on the nucleus and the electrons willingness to "pack down" a little bit because the "magic" is in the way the electrons behave when their numbers change. Atomic radius decrease moving across a row from left to right until we reach the inert gas at the end of that row, transition metals excepted. The inert gas has the largest radius of any element in its row, or Period, and it will be slightly bigger than the Group 1 element in its row, just as a note. The bottom line is that electron screening serves to make for larger atomic radii, but only going down a Group on the Periodic Table. The effects of screening are "nullified" moving across the chart from left to right in a given row, with the exception of the transition metals. Use the link below to see a simple but effective little chart of relative atomi sizes. Be sure to scroll down to see all the drawings.

Answer 2

Shielding affect acts as a barrier for proton to attract electrons, therefore the electrostatic force (the which attracts electrons to protons) becomes much less and electrons become further away from the nucleus of the atom. Because of this, the atomic size increases as you move down the group.

Answer 3

Electron shielding causes the outermost electrons to be held less tightly to the nucleus.

Answer 4

The atom gets bigger as you move down a group

Answer 5

shielding affect changes because valance electron goes far from nucleus

Answer 6

Down a group, the shielding generally increases.

Answer 7

More electrons in the atom = more blocking of the nucleus' charge.

Answer 8

The shielding effect is higher down in a group.

Answer 9

It's decreases