How do I do this?
Using the symbol of the previous noble gas to indicate the core electrons, write the electron configuration for each of the following elements.
(a) zirconium, Z = 40
(b) vanadium, Z = 23
[Kr]4d25s2
http://www.webelements.com/zirconium/atoms.html
To write the electron configuration for an element, you need to know the number of electrons in the atom.
(a) Zirconium (Z = 40): The symbol of the previous noble gas is Kr (krypton), which has an atomic number of 36. As electrons fill up orbitals in an atom, they go into specific energy levels and subshells.
Zirconium has 40 electrons, so you will need to place them in the appropriate energy levels and subshells. The electron configuration for zirconium is:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d2
The symbol of the previous noble gas, krypton (Kr, Z = 36), is used to indicate the core electrons. Therefore, you would write the electron configuration for zirconium as [Kr] 5s2 4d2.
(b) Vanadium (Z = 23): The symbol of the previous noble gas is Ar (argon), which has an atomic number of 18. Vanadium has 23 electrons, so the electron configuration is:
1s2 2s2 2p6 3s2 3p6 4s2 3d3
Using the symbol of the previous noble gas, argon (Ar, Z = 18), you would write the electron configuration for vanadium as [Ar] 4s2 3d3.