When you begin to fill d-orbitals there are some “anomalies” you must watch for. If you remember that ______electron-electron repulsion is energetically ______you should have no problem. For example:
Cr is not
1s 2s 2p 3s 3p 4s 3d
but rather
1s 2s 2p 3s 3p 4s 3d
The reason Cr fills this way is because the pairing of electrons in the 4s23d4 configuration results in greater electron-electron ______than the 4s13d5 configuration and is therefore less ______favorable.
Similarly Cu’s electron configuration is 4s13d10 rather than 4s23d9 because the electron-electron repulsion is ______and the energy is ______in the 4s2 configuration than the 3d10 configuration.
As you can see drawing orbital box diagrams and electron configurations for larger atomic number atoms can become tedious. To get around this problem you can write condensed or core configurations in which the electron configuration of the nearest noble gas is summarized by writing the symbol of the last noble gas in square brackets followed by the remaining electrons in full configuration. For example:
Cr becomes[Ar] 4s13d5
or[Ar]
4s 3d
One characteristic of atoms with unpaired electrons is that they are paramagnetic (attracted by a magnet). Atoms that have no unpaired electrons are diamagnetic (not attracted by a magnet). The more unpaired electrons an atom has, the greater its attraction to a magnet. It is important to realize that this phenomenon is not related to macroscopic magnetic properties.
Complete the table below.
Element / Core Configuration / Para or DiamagneticSc
V
Cr
Mn
Ni
Cu
Zn
Ga
As
Br
Kr
Sr
Zr
Mo
Ru
Ag
Sn
Te
Xe
Electron Configurations of Ions
Ions are formed when atoms gain or lose electrons. Main group atoms gain or lose electrons to achieve a stable ns2np6 configuration.
Main Group Cations
- Lose electrons in the reverse order to which they were added by the aufbau principle. For example:
Na and Na+
1s 2s 2p 3s 1s 2s 2p 3s
Main Group Anions
- Gain electrons to achieve an ns2np6 configuration. For example:
F andF-
1s 2s 2p 1s 2s 2p
Transition Metal Cations
- Lose the outer s electrons before losing d electrons. For example:
Fe[Ar]
4s 3d
Fe2+[Ar]
4s 3d
Fe3+[Ar]
4s 3d
It may seem odd that 4s fills before 3d because electrons in 4s are ______in energy than in 3d, but then electrons are removed from 4s before 3d because the electrons in 4s are ______in energy than 3d. This happens because the 4s and 3d orbitals are very close together and because once the 4s fills with electrons the 4s and 3d sublevels ______places with respect to the energies possessed by their electrons. As long as 4s is empty or singly occupied, 3d orbitals are at a ______energy. Once 4s is full, 3d orbitals are at a ______energy.
Complete the table below.
Ion / Ground State Orbital Diagram / Electron ConfigurationF- /
1s 2s 2p 3s 3p 4s 3d
P3- /
1s 2s 2p 3s 3p 4s 3d
Cr3+ /
1s 2s 2p 3s 3p 4s 3d
Co2+ /
1s 2s 2p 3s 3p 4s 3d
S2- /
1s 2s 2p 3s 3p 4s 3d
Cu2+ /
1s 2s 2p 3s 3p 4s 3d
Zn2+ /
1s 2s 2p 3s 3p 4s 3d
Ca2+ /
1s 2s 2p 3s 3p 4s 3d