SME
Inorganic Chemistry · Problem type
Electron count (18-electron rule)
Use this for “Count the valence electrons of [Co(CO)₄]⁻ and of Mn(CO)₅Cl. Does each obey the 18-electron rule?”
This is an example. Type your own values to start a new problem.
N
=
G
+
2
×
L
+
X
−
(
z
)
Formulas
N
=
G
+
2
×
L
+
X
−
z
18 = 8 + 2 × 5 + 0 − 0
Assumptions
•
Neutral counting: the metal brings its group number of electrons, as a neutral atom.
•
An L ligand (CO, NH₃, PR₃, an alkene) gives 2 electrons; an X ligand (Cl, H, CH₃) gives 1.
•
A negative charge adds electrons and a positive one removes them, so the count takes away the charge.
•
Most stable carbonyls and organometallics count 18; square-planar d⁸ metals (Pd, Pt, Rh, Ir) often stop at 16.
Step-by-step
WE KNOW
G = 8, L = 5, X = 0, z = 0
FIND
electron count (N)
Step 1 · Find electron count (N)
Use N = G + 2 × L + X − z
Add
the
metal’s
electrons,
2
for
each
L
and
1
for
each
X
,
then
take
away
the
charge.
N
=
8
+
2
×
5
+
0
−
0
N
=
8
+
10
N
=
18
→
18
electrons:
it
obeys
the
rule,
a
filled
valence
shell.
Check
Put the numbers back in. Both sides should match.
18 = 8 + 2 × 5 + 0 − 0 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.