The Number of Valence Electrons in Transition Metals

[nolansheow3G]

Hi, how do you know the number of valence electrons for transition metals? One of the homework questions asked "How many valence electrons are in Mn?" The answer is 7, but how can you tell?

[Sara Lakamsani 4D]

You need to write out the electron configuration of the element and then count the electrons in levels past the last noble gas, so for Mn, it would be the number of additional electrons it has after [Ar].

[Emmaraf 1K]

But @Sara Lakamsani 4C why do you include the 3d orbitals in the number of valence electrons? Doesn't valence electrons only come from the outermost shell which would be when n=4 for Mn? I understand the correct answer is 7 but why do you count the 2 4s electrons and the 5 3d electrons when counting valence since they are 2 different shells?