Two of most unique elements on the periodic table are hydrogen and helium. What makes them so unique and removed from the other groups on the periodic table?

Question

A) Unlike all other elements, hydrogen and helium are gases.
B) Unlike all other elements, hydrogen and helium are not considered metals.
C) Unlike all other elements, hydrogen and helium only have a maximum of 2 valence electrons.
D) Unlike all other elements, hydrogen and helium have very limited properties.

Answer 1

The best answer from the options provided is:

C) Unlike all other elements, hydrogen and helium only have a maximum of 2 valence electrons.

Here's why:

• Hydrogen has one electron in its outer shell, which is why it is placed in Group 1 (alkali metals) but behaves differently from metals because it can gain, lose, or share that electron.
• Helium has a completely filled outer shell with 2 electrons, placing it in Group 18 (noble gases), which are known for their lack of reactivity due to having a full valence shell.

While it is true that both hydrogen and helium are gases at standard temperature and pressure, the statement "unlike all other elements" may not hold true because there are other gases on the periodic table. Additionally, categorizing them as non-metals doesn't fully encapsulate their unique positions and characteristics. Therefore, option C specifically highlights their unique valence electron configurations, setting them apart from many other elements.