Electron Cloud

Erwin Schrödinger developed the concept of the electron cloud. He developed an equation that can calculate the probability of finding an electron in an area around the nucleus.

An electron cloud is a group of electrons that circulate the nucleus. Electrons are most likely to be found in the electron cloud. The higher density of electrons means that the chances of finding an electron are higher, which is why those regions are called electron orbitals.

Meaning of electron cloud

The electron cloud is a system of electrons surrounding the nucleus of an atom, and each orbital around the nucleus of the atom resembles a cloud-like structure. 

• Electron orbitals predict a certain level of probability of the presence of an electron.
• The number and types of orbitals increase with an increase in atomic number.
• There are four basic electron orbitals: s, p, d and f.
• There are always two electrons in every single orbital, which can be different by the property of spin.

Different models first gave a different idea about an atom, like the plum pudding model, Rutherford’s model, Bohr’s model. All these models assumed that an electron is a particle of well-defined mass that revolves around the nucleus like a planetary system. 

However, the electron cloud is like a dense cloud of probability that surrounds the nucleus. Because of electron cloud formation, it is impossible to find the simultaneous measurement of the position and momentum of an electron.

• Electron density is also a term used for describing electron clouds.
• Electron density is used to describe electron electronegativity, and the greater the difference in electronegativity between two atoms, the more the electron density is pulled toward, the more electronegative atom. 

Covalent bond

It is formed when the electron clouds of two atoms overlap with each other in a fixed direction.

Electron affinity

Electron affinity is the energy released when an electron is added to a neutral isolated gaseous atom to form a negatively charged ion.

• It is an energetic term as it describes the released energy of an electron. 
• It depends on stable electronic configuration; it does not regularly increase in a period.
•  It is measured in eV/atom, KJ/mol, or Kcal/ mol.
• High electron affinity means that the atom can more readily accept electrons, whereas a lower electron affinity indicates that an atom can not accept electrons easily.

Electron affinity is written with a negative sign, as energy is released in an exothermic process. In general, elements with more negative electron affinity are smaller and have the highest ionisation energies.

Various factors can affect the electron affinity, like:

• the atomic size
• nuclear charge and 
• the symmetry of the electronic configuration. 

Electron cloud on sigma bond

To know the influence of electron clouds on sigma bonds, let us first study sigma bonds.

• Sigma bonds are the strongest covalent bonds.
• They are formed by head-on overlapping between the atomic orbitals.
• Sigma bonding orbitals are cylindrically symmetrical orbitals.
• A sigma bond is formed first, then a pi bond because it has lower energy.
• Free rotation around the sigma bond is possible.

In sigma bonding, the electron cloud is symmetrical about the internuclear axis, which means it is not localised towards any one atom.

Electron cloud on pi bond

• Pi bonds are also covalent bonds.
• The sideway overlapping of atomic orbitals forms this bond.
• Unlike sigma bonds, free rotation about pi bonds is not possible.
• In pi bonding, there are two electron clouds present, in which one is above the plane of atomic nuclei, and the other is below it.

Electron cloud effect on polarisation

It occurs because of the distortion of an electron cloud. To be more precise, polarisation occurs when a negative cloud is distorted by the electric field around positive atomic nuclei in the direction opposite the field.

Conclusion

Electron clouds are the area subjected to the prediction of the presence of electrons. Understanding its formation and influence on different kinds of bonds is necessary to understand the meaning of electron clouds better.

Electron clouds describe that we can not know exactly where an electron is present at any given time, but we can know the probability of its presence in a specific area. Orbitals are those areas having a high likelihood of finding an electron with a dense electron cloud. 

There are four basic orbitals: s, p, d and f. electron affinity is also a character slightly influenced by an electron cloud. It is the energy liberated when an electron is added to a neutral atom. Sigma bonds have symmetrical electron clouds, while in pi bonds, the number of electron clouds is two.