Group IIa Characteristics
* Valence Electrons: Group IIa elements all have two valence electrons in their outermost energy level (the s-orbital).
* Reactivity: They are highly reactive metals, readily losing their two valence electrons to form +2 ions.
Electronic Configurations
Here's how you can deduce their electronic configurations:
1. Start with the general form: All Group IIa elements have a general electronic configuration ending in *ns²*, where 'n' is the principal quantum number (energy level) of the outermost shell.
2. Determine the principal quantum number (n): The principal quantum number corresponds to the period (horizontal row) the element is in on the periodic table.
3. Fill in the rest: To get the full electronic configuration, follow the filling order rules (Aufbau principle, Hund's rule, Pauli exclusion principle).
Examples:
* Beryllium (Be): Period 2, so n = 2. Electronic configuration: 1s² 2s²
* Magnesium (Mg): Period 3, so n = 3. Electronic configuration: 1s² 2s² 2p⁶ 3s²
* Calcium (Ca): Period 4, so n = 4. Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
* Strontium (Sr): Period 5, so n = 5. Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s²
* Barium (Ba): Period 6, so n = 6. Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s²
* Radium (Ra): Period 7, so n = 7. Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s²
Key Point: Notice that the last two electrons always fill the *s* orbital of the highest energy level. This explains their common chemical behavior and why they form +2 ions.
