There is only one electron inhabiting hydrogen and the compound therefore only has one shell, effectively making that shell the outer shell.
TL;DR
There is 1 electron in the outer shell of hydrogen.
Carbon has four valence electrons, so it will need four more electrons to fill its outer shell.
Enough to fill the outer-most shell. For most this is eight, but for helium it is two.
Carbon needs 4 electrons to fill up its outer shell. It has 4 valence electrons and can achieve a full octet by gaining 4 more electrons.
Beryllium will lose 2 electrons to satisfy the octet rule (to fill its outer shell).
It is because the two electrons in helium are placed in K-shell. The K-shell has the capacity of only two electrons. Therefore, in Lithium the third electron is placed in the L-shell. You can find the capacity of a shell to hold electrons by the formula 2n2 where n is the shell no.
Not by itself, no (that is, hydrogen is not a noble gas). A neutral hydrogen atom starts out with 1 electron, but it needs 2 electrons to fill its shell. Therefore, a hydrogen atom will often form 1 covalent bond with another atom, in order to gain that 1 extra electron it needs to fill its shell. Important note: Most elements need 8 electrons to get a full shell, but hydrogen is the exception: it only needs 2 electrons to get a full shell.
Sulfur has 6 electrons in its outer shell. Therefore, it needs 2 more electrons to fill its outer shell.
Carbon has four valence electrons, so it will need four more electrons to fill its outer shell.
Enough to fill the outer-most shell. For most this is eight, but for helium it is two.
Carbon has four valence electrons, so it will need four more electrons to fill its outer shell.
Nitrogen needs 3 more electrons to fill its outer shell. It has 5 electrons in its outer shell, and it typically needs a total of 8 electrons to achieve a full outer shell (octet rule).
Helium and neon will have their outer energy level filled with two electrons. Helium has 2 electrons in its only energy level, while neon has 8 electrons in its second energy level.
Carbon needs 4 electrons to fill up its outer shell. It has 4 valence electrons and can achieve a full octet by gaining 4 more electrons.
Beryllium will lose 2 electrons to satisfy the octet rule (to fill its outer shell).
Its atomic number is 7, and so it needs a further 3 electrons to fill its outer shell.
It is because the two electrons in helium are placed in K-shell. The K-shell has the capacity of only two electrons. Therefore, in Lithium the third electron is placed in the L-shell. You can find the capacity of a shell to hold electrons by the formula 2n2 where n is the shell no.
Helium does not form compounds because it is a noble gas with a full outer electron shell, making it very stable and unreactive. Its outer shell is already filled with electrons, so it does not need to gain, lose, or share electrons with other atoms to achieve stability.