Please tell me the trick to remember electronic configuration of lanthanides and the actinoides

Sure! Here is a step-by-step trick to remember the electronic configuration of lanthanides and actinides:

1. Start by writing down the atomic number of the element you want to remember the electronic configuration for. For example, let's take the lanthanide element with atomic number 57, which is Lanthanum (La).

2. Next, subtract 56 from the atomic number. In this case, 57 - 56 = 1.

3. Now, write down the electronic configuration of the noble gas that comes before the element. In the case of Lanthanum, the noble gas before it is Xenon (Xe), which has the electronic configuration [Xe] 5s^2 4d^10 5p^6.

4. Finally, add the number obtained in step 2 to the noble gas electronic configuration. In this case, 1 + [Xe] 5s^2 4d^10 5p^6 = [Xe] 5s^2 4d^10 5p^6 6s^2.

This trick can be applied to all the lanthanides and actinides. Just remember to adjust the atomic number and noble gas electronic configuration accordingly.

For example, for the actinide element with atomic number 92, which is Uranium (U), you would subtract 90 from the atomic number (92 - 90 = 2) and add it to the noble gas electronic configuration of Radon (Rn), which is [Rn] 7s^2 5f^14.

So, the electronic configuration of Uranium would be [Rn] 7s^2 5f^14 6d^1.

I hope this trick helps you remember the electronic configuration of lanthanides and actinides!