1. Chemistry 111
Periodic Trends

2. 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

3. 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

4. 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

5. 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

6. 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-