PERIODIC TRENDS Ionic 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 Na1s 2 2s 2 2p 6 3s 1 Na +1 1s 2 2s 2 2p 6 You lost the only electron on the 3 rd energy level so the valence energy level is now the 2 nd level so it is smaller

Mg vs Mg +1 Mg1s 2 2s 2 2p 6 3s 2 Mg +1 1s 2 2s 2 2p 6 3s 1 The valence electrons are still on the 3 rd 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]3s 2 3p 5 Cl -1 [Ne]3s 2 3p 6 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 S or S Ca 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 Ne Pb +1 or Pb +2 Rb +1 O -2 F -1 Pb +1