This sounds like Helium. It only has 1 electron shell and since it is the first shell, it only has room for 2 electrons, hence why it is full!
Barium has 0 unpaired electrons. It has a full outer shell of electrons, which is why it is a stable element.
An element reacts with another element by sharing electrons. The elements keep sharing electrons until both elements have a full outer shell.
This question is unclear. If you mean 3 full electron shells and nothing else, then it would be argon. But every element after argon has 3 full electron shells also, but they also have other shells with electrons. If you mean a full 3rd energy shell such as in having 3d10 electrons, then it would be Zn but Zn also has 4s2 electrons. So, the question is a vague one.
An element with 86 electrons is reactive because it is not a noble gas and does not have a full outer electron shell. Elements tend to react to achieve a stable electron configuration, such as by gaining or losing electrons to achieve a full outer shell.
Atomic mass does not directly indicate an element's reactivity. Reactivity is primarily determined by the number of electrons in the outer shell of an element (valence electrons). Elements with a full or nearly full outer shell (noble gases) are generally unreactive, while elements with few electrons in the outer shell (alkali metals) are highly reactive.
An element that does not require eight electrons for a full set of valence electrons is represented by the element symbol B. Boron only needs six electrons to complete its valence shell and achieve stability.
Helium
Helium has only 2 electrons and its energy level is full.
If the element has a full valence shell, such as the noble gases, then it is unreactive. It the element is missing few valence electrons of has few valence electrons, then the element is very reactive, such as the sodium.
an element is stable when it has a full outer shell of electrons. to abide by the octet rule it must have a shell of 2 then 8 electrons. An element with a full outer shell (8) will be stable and act like its nearest noble gas.
Barium has 0 unpaired electrons. It has a full outer shell of electrons, which is why it is a stable element.
There are many elements which have no unpaired electrons in their outer shells. The Noble gasses all have closed shells of valence electrons. The alkali earth metals (Beryllium, Magnesium, Calcium etc) also have no unpaired electrons, although their outer shell is not entirely full.
Helium has a full outermost energy level containing only two electrons.
Helium (He)
The element with a stable 2 valence electrons is helium. Helium has a full outer electron shell with 2 electrons, making it very stable and unreactive.
the element with seven valence electrons will be more reactive. The reason for this is that elements want to always want to have a full valence shell (they always want 8, like a noble gas). The element with eight valence electron is happy with its full shell and will not want to get rid of any electrons.
An element reacts with another element by sharing electrons. The elements keep sharing electrons until both elements have a full outer shell.