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PERIODIC TRENDSIonic Size
Ionic Radius
The distance from the center of an ion’s nucleus to its outermost electron
Cation – ion that has lost electrons (POSITIVE CHARGE)
Anion – ion that has gained electrons (NEGATIVE CHARGE)
Ionic Radius Trends:1. Cations will always be
smaller than their parent atoms
There are two reasons: Many times when electrons are lost by
an atom it loses enough to empty the outermost energy level
If the valence electrons are still on the same energy level, losing electrons decreases the electron-electron repulsion allowing the ion to get smaller
Na vs Na+1
Na 1s22s22p63s1
Na+1 1s22s22p6
You lost the only electron on the 3rd energy level so the valence energy level is now the 2nd level so it is smaller
Mg vs Mg+1
Mg 1s22s22p63s2
Mg+1 1s22s22p63s1
The valence electrons are still on the 3rd EL but Mg+1 will be smaller because there are fewer valence electrons so they are not repelling as much
2. Anions will be larger than their parent atoms
Why?When electrons are added
to an atom, there is an increase in the electron-electron repulsion causing the atoms’ radius to expand
Cl vs Cl-1
Cl [Ne]3s23p5
Cl-1 [Ne]3s23p6
Cl-1 has more electrons shoved on the valence energy level so there is more electron-electron repulsion hence a bigger size
Practice Problem: Which is smaller?
1. Ca or Ca+2
2. S or S-2
1. Ca+2
2. S
Easier Way???1. Look at valence energy level first
Higher the energy level, the bigger the atom
2. Look at # of protons second (only if needed)
More protons = smaller atom
3. Look at # of electrons last (only if needed)
More electrons = larger atom
Which is larger?
Rb+1 or S-2
Na+1 or O-2
F-1 or NePb+1 or Pb+2
Rb+1
O-2
F-1
Pb+1