Chemistry 111Periodic Trends

Atomic Size Atomic size increases from top to bottom

within a group and decreases from left to right across a period

Group – the number of protons increase, as does the number of energy levels (+ charge draws in – charge but increase in orbitals causes larger atoms)

Period – no added levels and an increase in + draws the e- closer to the nucleus

Ions An atom that has lost or gained e- in

order to have a filled outermost orbital

The amount of energy required to remove an e- from its orbital is called its ionization energy

It decreases from top to bottom within a group and increase from left to right across a period

Trends in Ionization Energy Group – the further away an e- is

from its nucleus, the easier it is to remove it from its current orbital; larger atoms have smaller ionization energies

Period – the number of protons increases in the nucleus but the shielding effect remains constant; added e- are attracted to the increased + charge

Trends in Ionic Size Positive ions are always smaller than

their respective atoms because they are removing e- and causing those that remain to be more attracted to the + charge which draws them into the centre

Negative ions are always larger because they have gained e- and now the attraction to the nucleus is not as great

Electronegativity It is the ability of an atom to attract e-

when forming a compound Representative Elements: Group trends - decrease from top to

bottom because there is greater distance from the nucleus and less attraction to + charge

Period trends – values increase from left to right because of the increased positive charge and space for added e-