Question

How grouping of similar things is useful to us

Answer 1

Answer:

As you pass from left to right and from one line to the next line below it, you are incrreasing the atomic number of each element, one proton at a time. As the protons increase, so do the electrons, and they fill up shells and start new shells. Chemical properties depend mainly on the number of electrons in the outermost shell (for transition state elements it doesn't work exactly by shells, since in the heavier elements it is possible for an electron in an inner shell to nonetheless be farther from the nucleus than some electrons in the outer shell, but that is an added complication). So, elements in the same group have the same number of outer, or valance electrons as they are known.