Answer:
The elements in the second, third, fourth and fifth periods that have the same number of electrons with the highest energy level that barium are beryllium (Be) magnesium (Mg), calcium (Ca ) and strontium (Sr).
Explanation:
The Electronic Configuration of the elements is the arrangement of all electrons of an element in energy levels and sub-levels (orbitals). The filling of these orbitals occurs in increasing order of energy, that is, from the orbitals of lower energy to those of higher energy.
There are 7 energy levels, numbered from 1 to 7, and in which electrons are distributed, logically in order according to their energy level. Electrons with less energy will be spinning at level 1.
Valencia electrons are the electrons found in the last electronic layer (called valence orbitals). This electrons allows to determine their location in the Periodic Table. All elements of the same group have the same number of valence electrons (This does not occur in transition metals). The valence electrons increase in number as one advances in a period. Then, at the beginning of the new period, the number decreases to one and begins to increase again.
So, in summary, those elements that belong to a group have the same number of electrons in their last or last layers, and the group number indicates the electronic configuration of their last layer, varying only the period of the element.
On the other hand, periods represent the energy levels that an atom has. That is, an element with five layers or energy levels will be in the fifth period.
Given this, <u><em>the elements in the second, third, fourth and fifth periods that have the same number of electrons with the highest energy level that barium are beryllium (Be) magnesium (Mg), calcium (Ca ) and strontium (Sr).</em></u> This is because they are in the same group (they have the same number of electrons in their last layer)
