Ionic Radius

[Ronak Naik]

Why does the trend going across a period start from bigger radii to smaller, and then once you hit the anions it again returns to a big radius and then decreases to small?

[Jessica Castellanos]

The ionic radius trend does show that anions are greater in size than their grounds state atoms and cations are smaller in size than ground state atoms because they lose electrons. However, for the general trend for atomic radius and ionic radius is greatest towards the bottom left because there are more shells as you travel down the periods. I hope this helps!

[MMckinney_4H]

As you increase the size of the nucleus across a period, the electrons are pulled in closer because of the higher number of protons with the electrons still being in the same shell. However, cations are smaller because when an atom loses an electron making it a cation, there is less electron-electron repulsion meaning that there doesn't have to be as much space. Imagine two people hate each other and never want to run into each other so they designate one half of the house to one and the other half to the other person. If there were to be a third person that entered the situation and all three people hated each other, there would need to be a bigger house so that each person could have there own space and not ever see the others. This is similar to the reason why with more electrons (people), the atom (house) is larger.

[Cynthia Gong 1L]

This is also because anions have more electrons, so there is more electron-electron repulsion present that causes the radius to be bigger.

[Ashley Nguyen 2L]

For ground state atoms, the ionic radii changes from bigger to smaller across a period because as the number of protons increases, the effective nuclear charge also increases, which pulls the electrons closer to the nucleus. However, anions follow a different pattern because they are bigger than their normal ground state atoms from their extra electrons. Cations, which lose electrons, have a smaller radii than their corresponding ground state atoms.