Both Ca and Sr are in Group 2 of the Periodic Table, with Sr below Ca (see image)..
Ionization energies
They are both metals, so they have relatively low ionization energies.
Sr is below Ca in the Group, so Sr has the lower ionization energy.
Electron configurations
Their electron configurations both end in ns².
For example, the electron configuration of Ca is [Kr]4s² and that of Sr is [Kr]5s².
Physical chsrscteristics:
Chemical characteristics
Both metals react with
• Hydrogen to form hydrides: M + H₂ ⟶ MH₂
• Oxygen to form oxides: 2M + O₂ ⟶ 2MO
• Nitrogen to form nitrides: 3M + N₂ ⟶ M₃N₂
• Halogens to form halides: M + X₂ ⟶ MX₂
• Water to displace hydrogen: M + 2H₂O ⟶ M(OH)₂ + H₂