Why do elements in a given group of the periodic table show similar chemical properties?

it is organized in how many electrons they have and how many electron shells(electron clouds) they are also in how the first collum can only bond with some ands second colum with others.

They have the same valence number. Meaning that all elements in group 1 have 1 unpaired electron on the outer shell. Are you just curious or are you working on a lab or somethin? Cause throw electronegativity in all this and some other properties and it gets a little more confusing.

By the number of electrons and how they react.
Ex) the group ALL the way to the right, the noble gases are ALL stable elemnts because they all have full energy levels.. it doesnt mean they have the same amount of electrons. it goes by their energy levels. and in noble gases all their energy levels are full

because that is how the periodic table is organized; by groups with similar chemical properties

chemical incest?