What Atoms of the Heavy Elements Really "Look Like"

We add the 6s orbital. Cesium has one electron, barium two. The innermost shells (1-3) are completely full. Shell 4 has the full complement of s, p and d orbitals, shell 5 has s and p.

The remaining three orbitals have two lobes and have their long axes along the axes of fourfold symmetry (where cube edges cross). The solid shown below has the symmetry of the overall set, which is called the cubic set.

Lanthanum adds an electron to a 5d orbital. Most of the remaining rare earth elements, however, add electrons by filling 4f orbitals.

Since all the changes take place two shells in, even removing the 6s shell doesn't bring the 4f electrons to the surface. Therefore, all these elements are very similar chemically, since their outer shells, even as ions, are virtually identical.

Here we have to make yet another concession to clarity. We can no longer show the individual d orbitals in color. The 3d orbitals are tan and the 4d orbitals are dark purple. Cerium adds an electron in a 4f orbital (green).

Three 4f orbitals are occupied

Four 4f orbitals are occupied

Promethium is unstable but its electron configuration is perfectly orthodox, with five 4f orbitals occupied.

Six of the seven 4f orbitals are occupied.

All of the seven 4f orbitals are occupied.

All seven 4f orbitals are occupied. Gadolinium adds a 5d orbital rather than a second electron to a 4f orbital.

All seven 4f orbitals are occupied. Second electrons are added to each 4f orbital.

With Lutetium we begin adding 5d orbitals for keeps. Shell 4 is now completely full.

Hafnium (72), the first element after the lanthanides, adds a second 5d orbital.

This is the Scandinavian neighborhood. Four elements (erbium, terbium, yttrium and ytterbium are named for the little Swedish town of Ytterby, Holmium is named for Stockholm and Hafnium for Copenhagen. Thulium is named for Thule, the ancient name for the far north.

One electron goes into a third p orbital

One electron goes into a fourth 5d orbital

Now all five 5d orbitals are occupied. and with Osmium we begin adding a second electron to each.

We begin filling the 6p orbitals.

An electron is added to a second 6p orbital

All three 6p orbitals are occupied and we add a second electron to each. Radon has a stable outer octet.

Bismuth used to be considered the last element with a stable isotope, but it is actually radioactive with an extremely long half life, longer than the age of the universe.

The 6p orbitals are in outline, the 5d orbitals in subdued colors and the 4f and 4d orbitals in pink and yellow. Details deeper within are all but impossible to see.

Like Lanthanum, we begin by adding a p orbital, in this case 6p.

We add a second 6p orbital.

We lose one 6p orbital but add two 5f orbitals. The 5d orbitals are dark purple.

We add a third 5f orbital

We add a fourth 5f orbital

We lose the 6p orbital and add two 5f orbitals to bring the total to six.

We add the seventh and final 5f orbital.

We add a 6d orbital.

The 5f orbitals are filled out by successively adding a second electron to each.

Last of the actinides adds a 6d orbital.