The allocation of electrons in an element’s atomic orbitals is described by its electron configuration. Atomic electron configurations follow a paradigm nomenclature in which all electron-containing atomic subshells are arranged in a sequence (with the number of electrons they possess written in superscript). The electron configuration of sodium, for example, is 1s22s22p63s1.
The conventional notation, on the other hand, regularly produces long electron configurations (especially for elements having a relatively large atomic number.The series of entirely filled subshells that correspond to a noble gas’s electronic configuration is substituted with the noble gas’s symbol in square brackets in the shorthand notation. As a result, sodium’s abridged electron configuration is [Ne]3s1.

This nomenclature for the distribution of electrons in atomic orbitals became popular immediately after Ernest Rutherford and Niels Bohr published their Bohr model of the atom in 1913.

Applications of electronic configuration:

• Calculating an element’s valency.
• Predicting a group of elements’ qualities (elements with similar electron configurations tend to exhibit similar properties).
• The interpretation of atomic spectra

Depicting electronic configurations:

Shells:

The principal quantum number determines the greatest number of electrons that can be accommodated in a shell (n). The shell number is articulated by the formula 2n2, where ‘n’ is the number of shells. Below is a table listing the shells, n values, and the total number of electrons that can be accommodated.

Subshells:

• The azimuthal quantum number (abbreviated as ‘l’) determines the subshells into which electrons are distributed.
• Subshells are determined by principal quantum numbers. As a result, when n = 4, four alternative subshells are possible.
• When n=4 is used. The s, p, d, and f subshells are called after the l=0, l=1, l=2, and l=3 subshells, in that order.
• The formula 2*(2l + 1) gives the maximum number of electrons that can be handled by a subshell.

Notation:

• Subshell labels are used to represent an atom’s electron configuration.
• The shell number (determined by the principal quantum number), the subshell name (determined by the azimuthal quantum number), and the total number of electrons in the subshell are all listed in superscript on these labels.
• For example, if two electrons are occupied in the first shell’s’s’ subshell, the notation becomes ‘1s2’.
• The electron configuration of magnesium (atomic number 12) can be expressed as 1s22s22p63s2 using these subshell labels.

Filling of Orbitals:

1. Aufbau’s Principle-

• The German word ‘Aufbeen,’ which means ‘to build up,’ inspired the name of this idea.
• According to the Aufbau principle, electrons will initially occupy less energy orbitals prior to moving on to higher-energy orbitals.
• The sum of the principal and azimuthal quantum numbers is used to calculate the energy of an orbital.
• Electrons are filled as: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p…

2. Pauli’s Exclusion Principle –

• According to the Pauli exclusion principle, an orbital can only hold a ulmost of two electrons with reverse spins.
• “No two electrons in the identical atom have the similar values for all four quantum numbers,” says this principle.
• As a result, if two electrons have the same principal, azimuthal, and magnetic numbers, they must have reverse spins.

3. Hund’s Rule-

• It states that before a subsequent electron is placed in an orbital, every orbital in a particular subshell is singly-occupied by electrons.
• The electrons in orbitals with only one electron have the same spin to maximize the total spin (or the same values of the spin quantum number).

Chemical Properties of Metals:

1. Reaction of metals with oxygen- Metal oxides are formed when metals react with oxygen. Metal oxides are formed when metals contribute electrons to oxygen. For example,
   4K + O2 → 2 K2O.
2. Reaction of metals with water-Some metals generate metal hydroxide when they come into contact with water, while others do not. The reactivity of metals with water varies. Sodium and potassium are very reactive metals. Alkalis such as sodium hydroxide and potassium hydroxide are formed when they react with water.
3. Reaction with dilute acids- Metals such as sodium, potassium, lithium, and calcium generate metal salts and hydrogen when they react vigorously with dilute HCl and H2SO4. Magnesium, zinc, iron, tin, and lead, on the other hand, do not react aggressively with acids.
4. Reaction of metals with salts of other metals- Metals that are more reactive will rapidly react with metals that are less reactive. The less reactive metal is displaced from its oxides, chlorides, or sulphides by the more reactive metal.

Chemical Properties of Non-Metals:

1. Reaction with water- Non-metals do not react with water. Phosphorus, for instance, is an extremely reactive non-metal that catches fire when exposed to air, which is why it is preserved in water to avoid contact with ambient oxygen.
2. Reaction with acids- There is no proof that any of the non-metals react with acids.
3. Reaction with Bases- The interaction of non-metals with bases is quite complicated. When chlorine reacts with bases like sodium hydroxide, it produces sodium hypochlorite, sodium chloride, and water.
4. Reaction with Oxygen-When non-metals react with oxygen, they generate oxides. Non-metal oxides are acidic or neutral in nature.

Conclusion:

The electronic configuration of elements is based on three principles or rules which are- Aufbau’s principles, Pauli’s exclusion principle and Hund’s rule. The electronic configuration of elements tells us whether the given element falls under the category of metals, non-metals, noble gases or metalloids. Generally, if the number of valence electrons is up to 3, the element is classified as metal. If the number of valence electrons is 4 to 7, then the given element is non-metal and if the number of valence electrons is generally 8, the given element is said to be a noble gas. The reactivity of the metals as well as that of non-metals is categorised with the help of their respective electronic configuration.