Why are hydrogen and helium alone in a row on the periodic table?

Answer 1

Thousands of people agree that this is where they should be. Hydrogen is an s block element with only one electron, and helium is a s block element too but it is also a noble gas which is why it is to the right.

Answer 2

Helium can only be located in Group 18 because its valence shell is complete with a 1s2 electron configuration, so it is unreactive and is said to be inert, and is a noble gas. Sometimes helium is placed at the top of Group 18 but with a space between it and the rest of the noble gases. This is to illustrate that helium's valence configuration is different from the other noble gases. The other noble gases have complete valence shells with eight valence electrons, with the configuration ns2np6 , because the rest of the noble gases are in periods 2-7, which correspond to the energy levels being filled with electrons. They are also unreactive, or inert.

Hydrogen can be placed in Group 1, even though it is a nonmetal, because it has one electron which it readily gives up to form H+ ions, just as the other Group 1 elements form 1+ ions. Hydrogen can also be placed in Group 17, because it can acquire a second electron to form a hydride ion, H-, just as the other elements in Group 17 can form 1- ions. Some periodic tables will place hydrogen above the first group of elements, but with a space between hydrogen and the other Group 1 elements.

Click on the related link to see a Periodic Table that has hydrogen detached from the rest of Group 1.

Answer 3

Because Hydrogen and Helium belong to different periodic 'groups'. The Hydrogen element belongs to the 'Hydrogen' group, whereas the Helium element belongs to the 'noble gas' group.

Answer 4

Helium has completely filled s orbitals. It is placed along with the noble gases which have completely filled p orbitals. Also helium is chemically inert and stable similar to noble gases.