The Quantum Address of an Electron
Every electron in an atom has a unique "address" defined by four quantum numbers
These numbers describe the energy, shape, orientation, and spin of the electron's orbital. Understanding these numbers is like having a GPS for the subatomic world.
Decoding the Zinc Atom
Zinc, with an atomic number of Z=30, is a fascinating transition metal
To understand its chemistry, we must first build its electronic configuration from the ground up. Following the Aufbau principle, electrons fill lower energy orbitals first. The ground state configuration of a neutral Zinc atom is [Ar]3d104s2.
The Catch
Forming the Cation
When a transition metal like Zinc loses an electron to form a cation, a common pitfall awaits many students. One might assume that the last electron added (in the 3d subshell) is the first to leave. However, this is not the case! Electrons are always removed from the outermost principal quantum shell first. Since n=4 is higher than n=3, the electrons in the 4s orbital are the first to go.
Therefore, to form the Zn+ ion, we remove exactly one electron from the 4s orbital, leaving us with the configuration [Ar]3d104s1.
Zeroing in on the Outermost Electron
With the configuration of Zn+ established, our focus shifts entirely to the lone electron in the 4s orbital
This is the "outermost" electron the question is asking about.
The Final Calculation
The azimuthal quantum number, l, dictates the shape of the orbital
For any s-orbital, regardless of its principal quantum number, l=0, indicating a perfectly spherical shape.
The magnetic quantum number, m, describes the spatial orientation of this shape and can take any integer value from −l to +l. Since our azimuthal quantum number l is 0, the math becomes incredibly simple. The only possible value for m is 0.
Final Answer: The magnetic quantum number of the outermost electron of the Zn+ ion is 0.