Given below are some elements of the modem periodic table:
${}{4}Be$,
${}{9}F$,
${}{14}Si$,
${}{19}K$,
${}_{20}Ca$
(i) Select the element that has one electron in the outermost shell and write its electronic configuration.
(ii) Select two elements that belong to the same group. Give reason for your answer.
(iii) Select two elements that belong to the same period. Which one of the two has bigger atomic size ?
(i) ${}{19}K$, its electronic configuration is: 2,8,8,1
(ii) ${}{4}Be$,
${}{20}Ca$ (Both have two valence electrons,and in a group valence electrons remain the same).
(iii) ${}{4}Be$ and
${}_{9}F$ belong to same period. Atomic size of Be is bigger because in a period, atomic size decreases due to increased nuclear charge.