Why do all elements of the same group have similar properties?

Elements in the same period may have

Elements A, B, C, D, E, F, G, H, I, J and have atomic masses 13, 3, 97, 25, 7, 35, 9, 30, 50, and 19 respectively. According to law of octaves, which elements would have similar properties? Explain.

a) What property do all elements in the same column of the periodic table as boron share? b) What property do all elements in the same column of the periodic table as fluorine share?

What are the similar properties of Li and Mg.

a] Why are sodium and chlorine placed in the same period in the Modern Periodic Table? b] Why do elements placed in the same group of the periodic table have similar chemical properties? c] Who proposed the modern periodic law? On which fundamental property of an atom is it based?

What property do all elements in the same column of the Periodic Table as boron have in common?