Cu: [Ar]3d104s1
1st I.E. is relatively small (one 4s e- is removed)
2nd I.E. is relatively large (one 3d e- is removed from full-filled 3d-orbitals, extra E is required)
Zn: [Ar]3d104s2
1st I.E. is relatively large (one 4s e- is removed from full-filled 4s-orbital, Zeff also increases from Cu to Zn)
2nd I.E. is relatively small (another 4s e- is removed to achieve all full-filled orbitals, relatively stable)