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PERIODICITY

ACROSS PERIOD 2

-Moving from Lithium to Neon,the number of shells and inner electron remain same.But the number of proton is increase.The increasement of number of proton will also make effective nuclear charga,Zeff increase.Thus,the attraction between nucleus and the outer electron stronger from Li to Ne .Therefore,the atomic radii become smaller across period 2.So, lithium has the biggest atomic radius and neon has the smallest atomic radius in period 2. Atomic radius generally decrease across a period from left to right.

DOWN GROUP 2

-Moving down from beryllium to radium,the number of shells and inner electron increase and effective nuclear charge,Zeff remain same.But moving down the group 2,shielding effect increase because the nuclear core is farther removed from the valence electrons.This causes the attraction between nucleus and the outer electron become weaker.Thus,the atomic radii become smaller down the group.So,beryllium has the smallest atomic radii and radium has the biggest atomic radii.Atomic radius generally increase down a group from top to bottom.

different RADIUS of atom be & ion be2+ (metal)

-A neutral atom Be donates 2 electron from the outermost shell to form a cation,Be2+.Thus,the number of electron in Be2+ is less than in Be.This means the number of inner electron in Be2+ is also less than in Be.So,there are less electrons repulsion in Be2+ than Be.The effective nuclear charge,Zeff in Be2+ is higher than in Be.This causes the attraction between nucleus and the outermost electron in Be2+ is stronger than in Be.The electron shrinks and causing the ionic radius of Be2+ smaller than Be.So, cation ion,Be2+ is always smaller than a neutral atom,Be.

different radius of atom o and ion o2-(non-metal)

-Two electron was added into the outermost shell of neutral atom O to form an anion O2-.Thus,the number of electron in anion O2- is more than in neutral atom O.So,there will be more electrons repulsion in anion,O2- than O atom and causes the electron to be pushed apart and far from the nucleus.This means that the forces of attraction between nucleus and the outer electron in O2- is weaker than in O atom,Therefore,electron cloud of O2- is bigger than O atom.Thus,the ionic radius of O2- is bigger than the neutral atom O.Hence,anion is always larger than a neautral atom.