That is beryllium.
The atom of an element in the third period of the Periodic Table has 3 energy levels and so on. Also, atoms of elements in the same group have the same no. of valence electrons.
If it has electrons in three different energy levels, then it must be in period 3 of the periodic table. To have the fewest electrons, it would be in group 1. So, the element in group 1, period 3 is sodium (Na).
The element magnesium has four electron energy levels and two electrons in its outer energy level in the neutral atom. Use the link to Wikipedia for more details.
going down a group, each element gains 1 shell (energy levels)
the group number shows the number of electrons in the outermost energy levels. forexample sodium (Na) have 1 electron in the outermost shell and is placed in the group 1. Elements are grouped in rows depending on their energy levels, or valence electron numbers. Columns of elements are those that are chemically similar, or react
arsenic belongs to V-A group of periodic table it has 5 electrons in its outermost energy level.
The Group Number of the Element you're working on determines the number of Valence Electrons. Valence electrons are electrons in the outside energy level.
5 valence electrons.
the period number tells which is the highest energy level occupied by the electrons
Group 18 or noble gases.
Strontium has 5 energy levels in group 2.It is represented by symbol Sr and has five energy levels K,L,M,N and 0.
The trend of atomic radius increases down a group on the periodic table. This occurs because each successive element down a group has another energy level. As more electrons are added, more energy levels are needed to hold the electrons.