Write the number of periods the modem periodic table has. How do the valency and metallic character of elements vary on moving from left to right in a period? How do the valency and atomic size of elements vary down a group?
A modern Periodic table has 7 periods in it.
When moving from left to the right in a period, the valency of the elements increases from 0 to 4 and then it decreases to 0.
As we move from left to right, the nuclear charge on elements increased due to increase in the number of protons. With increase in the nuclear charge, the force with which the valence electrons are pulled becomes stronger and becomes difficult for the atoms to lose the outermost electrons. Therefore, when we move from left to right in a period, the metallic character of the element decreases.
Since the elements have same no. of valence electrons in a group, so valency remains the same in a group.
When we move down in a group, the size of the atom increases due to introduction of a new shell of electrons at each step.
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