Tanner's General Chemistry



Atoms - Part 8 - Orbitals and the Periodic Table

With the filling of the 3s and 3p orbitals the first ionization potential shows an increase similar to that with the 2s and 2p orbitals with a maximum at the noble gas argon.

Figure 20.

The filling of the 3s and 3p orbitals completes the third row of the periodic table.

The filling of the next period is more involved because it includes the 4s, 3d, and, 4p orbitals. The filling of the 4s, 3d, and 4p orbitals completes the fourth row of the periodic table. There is a total of 18 elements in this row, 2s, 10d, and 6p electrons.

The pattern of filling of orbitals in this period is more complex. The 4s orbital is closer to the nucleus than the 3d orbitals and has lower energy. So the first two electrons go into the 4s orbital. The electrons fill the 3d orbitals in a progressive sequence with exceptions at vanadium and copper due to the particular stability of the half-filled d5 and the filled d10 levels.

4s 3d 4s 3d
K 1 0 Mn 2 5
Ca 2 0 Fe 2 6
Sc 2 1 Co 2 7
Ti 2 2 Ni 2 8
V 2 3 Cu 1 10
Cr 1 5 Zn 2 10

In general, energy increases with the principle quantum number n. But in some cases the lowest sublevel of one shell is at a lower energy than the highest sublevel of a lower shell. The 4s orbital is at a lower energy than the 3d orbital in most cases.

Figure 21.

Below is a table showing the filling of the 5s and 4d orbitals.

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d
Rb 2 2 6 2 6 2 10 6 1
Sr 2 2 6 2 6 2 10 6 2
Y 2 2 6 2 6 2 10 6 2 1
Zr 2 2 6 2 6 2 10 6 2 2
Nb 2 2 6 2 6 2 10 6 1 4
Mo 2 2 6 2 6 2 10 6 1 5
Tc 2 2 6 2 6 2 10 6 2 5
Ru 2 2 6 2 6 2 10 6 1 7
Rh 2 2 6 2 6 2 10 6 1 8
Pd 2 2 6 2 6 2 10 6 10
Ag 2 2 6 2 6 2 10 6 1 10
Cd 2 2 6 2 6 2 10 6 2 10

The Periodic Table

Alkali Metals Rare Earth Metals
Alkali Earth Metals Halogens
Transition Metals Noble Gases
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac #
* Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
# Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

The transition metals, involving the filling of the d orbitals, vary less in properties than the elements involving the filling of s and p orbitals. The last two rows, lanthanides and actinides, are set aside for reasons of space on the page. They involve the filling of f orbitals. The lanthanides and actinides do not vary much in chemical properties as the f orbitals are deeply buried.

In general, atoms increase in size moving downward in the periodic table. In a row they tend to decrease in size from left to right due to the increasing nuclear charge.

This ends the quick course in atoms.

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