Clarity on Electronic Configuration

We know that an electron is an atom that is characterized by a set of four quantum numbers. The principal quantum number denoted by ‘n’ defines the main energy level which is called a shell. As we know, orbitals (s, p, d, f) are about the filling of electrons in different subshells. So, the electronic configuration is defined as the distribution of electrons into orbitals of an atom. The electronic configuration is given by the Aufbau principle.

In the periodic table, where the element is located reflects the quantum numbers of the last orbital filled. Here we will notice a direct connection between the electronic configuration of the elements and the periodic table. 

ELECTRONIC CONFIGURATION IN PERIOD

There are different principles for filling the electrons in the shell. But the most famous and widely used method is the Aufbau principle. The method to fill the shell of an atom is discussed below-

In the periodic table, the successive period is associated with the filling of the next higher principal energy level (n=1, n=2 …). We can see that the number of elements in each period is double the number of atomic orbitals available in the energy level that is being filled. 

The first period ( n=1) can be started by filling the lowest level (1s) and hence has two elements- Hydrogen (1s1) and helium (1s2). Now, the first shell (K) is completed. 

The second period (n=2) starts with helium and the third electron enters the 2s orbital. The next element which is beryllium has four electrons and has the electronic configuration 1s22s2. Going ahead to the next element, which is the Boron, the 2p orbitals are filled with electrons when the L shell is completed at neon (2s22p6).  Hence, 8 elements are there in the second period. 

The third period (n=3) begins at sodium. The added electrons enter a 3s orbital. Simultaneously filling of 3s and 3p orbitals give rise to the third period of 8 elements starting from sodium to argon.

The fourth period (n=4) starts at potassium. The added electrons fill up the 4s orbital. Now, before the 4p orbital is filled, the filling up of 3d orbitals becomes favorable and it is called the 3d transition series of elements. It starts from scandium (Z=21) which has the electronic configuration of 3d14s2. The 3d orbitals are filled at zinc (Z=30) with electronic configuration 3d14s2.

The fourth period ends with Krypton while filling up the 4p orbitals. Together there are 18 elements in the fourth period. 

The fifth period (n=5) beginning with rubidium is very similar to the fourth period and has 4d transition series starting from yttrium (Z=39) and ending at xenon filling up of the 5p orbitals. 

The sixth period (n=6) has 32 elements and electrons enter successively into 6s, 4f, 5d, and 6p orbitals, in order. Filling up of the 4f orbitals begins with cerium (Z=58) and ends at lutetium(Z=71) giving a 4f inner transition series called lanthanide series. 

The seventh period (n=7)is also similar to the sixth period. Successively filling up of the 7s, 5f, 6d, and 7p orbitals include most of the man-made radioactive elements. This period ends with an element having atomic number 118 belonging to the noble gas family. Filling the 5f orbitals after actinium (Z=89) gives the 5f-inner transition series known as the actinide series. 

The 4f and 5f inner transition series of elements are separately placed in the periodic table. 

ELECTRONIC CONFIGURATION OF COPPER

Let’s talk about the electronic configuration of copper-

Copper has an atomic number of 29. So, The electronic configuration of copper is 1s22s22p63s23p64s13d10. This can also be written as [Ar] 3d104s1. It is because the half-filled and filled electronic configurations have lower energy or are more stable. Therefore, to become stable, the 4s orbital will go to 3d orbital so that 3d orbitals become fully filled orbitals. This is an exception. Hence, it does not follow the Aufbau principle. 

CONCLUSION- 

The electronic configuration is about the position of electrons around the nucleus. Elements in the same group in the periodic table have similar electronic configurations. It is because an electron is responsible for similar chemical properties. K shell to Q shell is subdivided into sets of orbitals