chem 問題..高手唔該幫手

我地諗下一個atom, 係由 nucleus 同埋 electrons 形成,
而down the group 即係 period 愈黎愈大
period即係 no. of occupied electron shells
咁佢愈多層shells, 舊野米愈大舊囉...
所以atomic size大了..

When down the group, the principal quantum number increase, new quantum shell are formed which is much far away from the nucleus, the attraction between outer electron decrease, the atomic size increase.