[jamesgarbachov]

Explain why transition metals show great similarities within a period as well as within a give vertical group?

I don't know how to explain it

[chenbeier]

What is the electron configuration of these metals? Maybe the coin drop now.

[P]

Yes - look at how the shells fill to be in the most stable states. Look at how electrons are taken from lower levels to fill or half fill outer d shells, so that they are more stable. Seeing as the chemistry is determined by the electrons would we not expect similar reactivity for elements with similarly filled outer shells?

The transition metal elements usually have their d shells empty, full or half full where possible and they take electrons from lower p orbitals to balance the d orbitals into one of these configurations.  Can you work it out from here?

[Flatbutterfly]

Electron configurations of transition metals:
SHRIVER  and ATKINS, Inorganic Chemistry 4th ed (2006: note 4th ed and it has ten authors, so any mistakes at the fundamental level have probably been corrected).  Fig 1.22 (p 20) shows that except for K and Ca the 4s AO  is ALWAYS higher in energy than the 3d AOs BUT (p 22): “the determination of actual ground states by spectroscopy and calculation shows that is advantageous to occupy orbitals predicted to be HIGHER in energy (the 4 s orbitals).  The explanation for this order is that the occupation of orbitals of higher energy can result in a reduction in the repulsion between electrons that would occur if the lower energy 3d were occupied.” 
The Full Story of the Electron Configurations of the Transition Elements W. H. Eugen Schwarz J. Chem. Educ., 2010, 87 (4), pp 444–448
 4s is always above 3d!  F. L. Pilar, J. Chem. Ed. 1978, 55, 2.

https://en.wikipedia.org/wiki/Electron_configurations_of_the_elements_(data_page)