Starting where the last blog left off, you hopefully remember that electrons are pair with opposite spin in orbitals, which sit within sub-shells, within shells described by the principle quantum number (n). We can show electron configurations on an energy diagram as shown below:
When it comes to assigning electrons to orbitals, the simplest atom is hydrogen (H), which has one electron in the 1s sub-shell, as shown below:
The single electron is placed in the lowest energy orbital (1s) first, and denoted here by an arrow, with the direction, up or down, showing the spin. In helium (He), the second electron has opposite spin (down-spin) and is paired with another electron in the 1s:
By the time we get to nitrogen, each p orbital contains one electron, and the 2p sub-shell is half-full. This imparts some stability, which is something that ties into ionisation energies:
Oxygen has one more electron, which is paired with one of the electrons already in the 2p sub-shell with opposite spin:
The diagrams above are a good way of visualising the arrangement of orbitals, however, it would be extremely lengthy to draw out every time. We usually represent the electron configuration of a substance spd notation, as shown below:
So this means that the spd notation of oxygen is 1s22s22p4.
The periodic table can be separated into three blocks; s, p and d blocks. The s-block is comprised of elements who's last sub-shell is an s sub-shell and so on...
So, if we pick out phosphorus (P) for example, as we know it is in the p block, its last occupied sub-shell would be the 3p and as it is three places into the p block, the 3p sub-shell would have an occupancy of 3, so 3p3. Overall the spd notation of phosphorus would be 1s22s22p63s23p3.
In summary:
- Electrons fill the lowest energy sub-shell first.
- Electrons fill sub-shells until they are half full and then pair with electrons of opposite spin to fill the sub-shell.
- An element's position in the periodic table can tell you its electron configuration.
No comments:
Post a Comment