Question

"The number of elements in each period is twice the number of atomic orbitals available in the energy level that is being filled."
Can you please explain the meaning of this? please make it fast I have a test tomorrow please!!!!

Answer 1

Elements are twice the number of the orbitals. 

Lets understand it by taking the elements of 4th period. In fourth period there are 18 elements. The types of the subshells used in 4th period are s, p and d so,

Number of orbitals of s subshell = 1

Number of orbitals of p subshell =3

Number of orbitals of d subshell =5

Total number of orbitals = 9

Total number of elements = 18 which is twice the total number of orbitals.

Answer 2

Answer:

According to Pauli's Exclusion Principle we can actually fill two electrons i.e. one clockwise and other is anti-clockwise in every Atomic orbital.

Since the number of elements in a period depends on Atomic number which is nothing but number of electrons in an atom filled in different shells.... hence the number of elements in each period is twice the number of atomic orbitals available in that energy level.