Which of the following species is isoelectronic, Ba2+ and Ba, Al3+ and Ar, Cl - and Na+ , or Sr2+ and Se2-
Check out Cl^- and Na^+ as well as Sr^2+ and Se^2-
To determine which species are isoelectronic, we need to compare their electron configurations. Isoelectronic species have the same number of electrons.
Let's first look at the options:
1. Ba2+ and Ba:
Barium (Ba) has atomic number 56 and the electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s².
Ba2+ means that it lost 2 electrons, so the electron configuration would be 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶.
2. Al3+ and Ar:
Aluminum (Al) has atomic number 13 and the electron configuration is 1s² 2s² 2p⁶ 3s² 3p¹.
Al3+ means it lost 3 electrons, so the electron configuration would be 1s² 2s² 2p⁶.
Argon (Ar) has atomic number 18 and the electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶.
3. Cl- and Na+:
Chlorine (Cl) has atomic number 17 and the electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁵.
Cl- means it gained 1 electron, so the electron configuration would be 1s² 2s² 2p⁶ 3s² 3p⁶.
Sodium (Na) has atomic number 11 and the electron configuration is 1s² 2s² 2p⁶ 3s¹.
Na+ means it lost 1 electron, so the electron configuration would be 1s² 2s² 2p⁶.
4. Sr2+ and Se2-:
Strontium (Sr) has atomic number 38 and the electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s².
Sr2+ means it lost 2 electrons, so the electron configuration would be 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s⁰.
Selenium (Se) has atomic number 34 and the electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴.
Se2- means it gained 2 electrons, so the electron configuration would be 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶.
Now, let's compare the electron configurations:
Ba2+ and Ba have the same electron configuration, so they are isoelectronic.
Al3+ and Ar have different electron configurations, so they are not isoelectronic.
Cl- and Na+ have different electron configurations, so they are not isoelectronic.
Sr2+ and Se2- have different electron configurations, so they are not isoelectronic.
Therefore, the correct answer is Ba2+ and Ba.