Periodicity
Read our general notes on Risk Assessment
Hi. K is in the 4th period of the Table. The transition elements from Sc are in the same line as the 4th Period elements like K, but are called 3d elements. Why 3? Is it because H and He are not regarded as main block elements? Thank you.
Ulex says ...
Not quite! K, Ca are said to be in the 4th Period because the electrons which are being added as you go through the main groups of the period are going into subdivisions of main quantum energy level 4: 4s in the case of K, Ca and 4p for those from Ga to Br. This is because the energy of the 3d orbitals is initially above that of the 4s.
When you reach scandium the energies of the 4s and 3d orbitals become very close together, and below 4p, so for Sc to Zn further electrons go into the 3d orbitals. There are small anomalies with Cr and Cu but basically it is the filling of the 3d orbitals which is the focus of attention between Sc and Zn.
Having said all this, you will occasionally see (mostly older) versions of the Periodic Table in which H and He are thought to be anomalous and are not designated Period 1, the numbering starting with the Li period instead, but this is rare nowadays.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
Rate this page or react
Share your views on this page, 0 ratings so far
updated: 03 June 2007
