To determine which pairs of elements do not have to satisfy the octet rule for stability, we need to understand which elements are exceptions to this rule.
The octet rule states that atoms tend to form compounds in ways that give them eight valence electrons, achieving a noble gas configuration. However, there are exceptions:
1. Group 1 Elements (Alkali Metals): These elements, including potassium (K) and sodium (Na), do not follow the octet rule strictly because they achieve stability by losing one electron to form cations with a complete octet in their next inner shell.
2. Group 2 Elements (Alkaline Earth Metals): These elements also deviate from the octet rule by losing two electrons to attain stability.
3. Hydrogen (H) and Helium (He): Hydrogen achieves stability with only two electrons, and helium is already stable with two electrons in its outermost shell.
Now, let's analyze the pairs given in the question:
1. Potassium (K) and Sodium (Na):
- Both potassium and sodium are Group 1 elements.
- They achieve stability by losing one electron.
- Therefore, they do not strictly follow the octet rule.
2. Neon (Ne) and Argon (Ar):
- Both neon and argon are noble gases with already complete octets.
- They naturally have a full set of eight electrons in their outermost shell.
- They do follow the octet rule because they are stable without needing to gain or lose electrons.
3. Oxygen (O) and Fluorine (F):
- Both oxygen and fluorine are nonmetals that aim to gain electrons to complete their octet.
- They follow the octet rule to achieve stability by gaining electrons.
4. Helium (He) and Hydrogen (H):
- Helium is stable with two electrons and does not need eight to be stable.
- Hydrogen achieves stability with only two electrons as well.
- They do not strictly follow the octet rule.
Among the pairs, many elements do not rely on the octet rule, but considering Group 1 where elements like potassium and sodium inherently do not follow it, we identify:
Potassium (K) and Sodium (Na) as the pair that does not have to satisfy the octet rule for stability.
Final Answer:
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