All elements have energy levels, but they are never described as unfolded. The energy levels are like layers, similar to how a gobstopper has different layers of color. They cannot be unfolded.
The element in period 3 with 8 electrons in its outermost energy level is chlorine (Cl).
Helium has a full outermost energy level containing only two electrons.
It is the most stable element in the universe and does not need anymore electrons. Its outermost energy level is full.
The element carbon
The element with its outermost electron in the 7s1 orbital is francium (element 87). Its outermost electron is in the 7th energy level (n=7), specifically in the 7s subshell.
Mg -magnesium.
Helium (He)
Well, darling, that element you're looking for is helium. It sits pretty on the periodic table with its full outermost energy level of 2 electrons, living its best life. So, there you have it, helium is the sassy star of the show with its energy level on lock.
An atom with an incompletely filled outermost energy level is likely to be reactive. This is because atoms tend to gain, lose, or share electrons to achieve a stable outer electron configuration. Atoms with incomplete outermost energy levels are looking to fill or empty their outermost energy level to achieve stability.
Valence electrons are found in the outermost energy level of an atom, also known as the highest principal energy level. These are the electrons involved in chemical bonding and determining the reactivity of an element.
Helium has only 2 electrons and its energy level is full.
The velence electron will vary for element to element and can have 1 to 8 valence electrons.