Question

Use principles of atomic structure to Explain why in aqueous solution,
(a) potassium forms 1+ but not a 2+ ion
(a) Ti3+ is colored but Sc3+ is not.
(b) Ti2+ is a reducing agent but Ca2+ is not.

Answer 1

19K is 1s2 2s2 2p6 3s2 3p6 4s1
K can lose the 1 4s1 easily but the next shell is a closed shell.

Sc^3+ has no unpaired electrons. Ti^3+ has an unpaired electron. Here is the electron configuration.
21Sc is 1s2 2s2 2p6 3s2 3p6 3d1 4s2. Note that the +3 ion is formed by removing the 4s2 electrons and the 1 3d1.

22Ti is 1s2 2s2 2p6 3s2 3p6 3d2 4s2.
Note that the +3 ion is formed by removing the 4s2 electrons and ONE of the 3d2 electrons. That leaves an unpaired electron.

c.
20Ca 1s2 2s2 2p6 3s2 3p6 4s2
So Ca^2+ is formed by removing the 4s2 electrons. The next shell down is a closed shell.
Look at the Ti^2+ ion and where it can go (compare with the Ti^3+ above).

Answer 2

thank you!