Write the number of periods and groups present in the Modern periodic table .State the changes in valency and metallic character of elements as we move from left to right in a period. Also state the changes, if any, in the valency and atomic size of elements as we go down a group.
Answers
Modern periodic table contains seven periods and 18 groups. All elements in periodic table are divided into four blocks: s, p, d and f.
From left to right electronegativity, a tendency of an atom to attract and form bonds with electrons increases. Most of elements follow tendency to get 8 electron in their outer shell to finish octet. From left to right most of elements with less than half full valance shell are required significantly higher energy to gain the electron as compare to losing the electron. Elements with more than half full valance shell are easily able to get an electron as compared to lose. Due to this reason elements from left side are easier to lose electron to form bonds while elements from right side are more efficient in getting the electron to finish the octet in outer shell.
Metallic nature is defined as easiness for an element to lose an electron. From left to right in a period metallic nature is decreased due to stronger attraction between nucleus and valance electrons. Metallic nature down the group increases due to bigger atomic size and lesser attraction between nucleus and valance electrons.
In each group, elements contain similar number of electrons in their outer shell so valency remains unchanged down the group. Down the group atomic size of elements increases because outer shells are having weaker attraction between nucleus and valance electrons.