To determine which pairs of elements do not have to satisfy the octet rule for stability, we need to understand the rules each element follows to achieve stability:
1. Potassium (K) and Sodium (Na):
- Both potassium and sodium belong to group 1 of the periodic table, known as alkali metals.
- These elements achieve stability by losing one electron, which means they do follow a rule similar to the octet rule (they achieve stability by having a noble gas configuration when they lose an electron).
2. Neon (Ne) and Argon (Ar):
- Both neon and argon are noble gases, which belong to group 18 of the periodic table.
- These elements are inherently stable because they already have a complete set of eight valence electrons, fulfilling the octet rule from the start.
3. Oxygen (O) and Fluorine (F):
- Oxygen and fluorine are non-metals found in groups 16 and 17, respectively.
- These elements achieve stability by gaining electrons to complete their octet, thereby following the octet rule.
4. Helium (He) and Hydrogen (H):
- Helium, a noble gas in group 18, is stable with just two electrons, following what we call the "duplet rule" rather than the octet rule.
- Hydrogen, when forming covalent bonds, achieves stability by having two electrons (similar to helium), thus following the duplet rule as well.
Therefore, analyzing the pairs:
- Potassium (K) and sodium (Na): These follow the octet rule by losing one electron.
- Neon (Ne) and argon (Ar): These noble gases are already stable and do not need to follow the octet rule.
- Oxygen (O) and fluorine (F): These follow the octet rule by gaining electrons.
- Helium (He) and hydrogen (H): These follow the duplet rule.
The pairs that do not need to satisfy the octet rule for stability are:
- Neon (Ne) and argon (Ar)
- Helium (He) and hydrogen (H)
Thus, there are 4 such pairs that do not have to satisfy the octet rule for stability:
- Neon (Ne) and argon (Ar)
- Helium (He) and hydrogen (H)
