Anything and everything has a pattern to follow and function accordingly, and these functions, methods, approaches, and strategies are all together in the vastest branch of science, which is mathematics. According to the father of mathematics, Archimedes, it has shaped the world by introducing people to unique counting and calculating perspectives.
To narrow it further, geometry itself is divided into two more broad categories, namely Molecular Geometry and Electron Geometry, which refer to the positioning and ordering of electrons, neutrons, and atoms to provide specific and most suitable angles, positions, and shapes to molecules.
Molecular geometry is the configuration of atoms in a molecule, mostly comparative to one central atom, whereas the configuration of pairs of electrons around a central atom is called electron geometry.
These distinctive and conceptual branches of geometry are discussed extensively in this article.
Molecular Geometry: 3-Dimensional Shape
The characterization of atoms in a molecule arranged in a 3-dimensional space is known as molecular geometry. Some approaches, like spectroscopy and diffraction analysis, are usually deployed for understanding molecular geometry.
Certain theories are utilized to help in getting information about the configuration of molecules like hybridization theory, Lewis concept, and VSEPR theory.
Hybridization Theory
Hybridization theory describes the presence of covalent bonds in atomic molecules.
The process of mixing orbitals having the same energy but different in shape to form hybrid orbitals with the same number, shape, and energy is the basic process of hybridization.
Types of Hybridization:
Some types of hybridization are as follows:
- sp hybridization: 1s and 1p orbitals
- sp² hybridization: 1s and 2p orbitals
- sp³ hybridization: 1s and 3p orbitals
Lewis Theory
An American scientist (G.N. Lewis) first introduced the concept that each atom shares two electrons to form a covalent bond by bond pairing, whereas the pair of electrons uninvolved in any type of bonding is called a lone pair.
Lone Pairs
It has been observed theoretically and practically that molecular geometry does not possess lone pairs in its central atom in the molecule due to the more incredible amount of space that it occupies than a single bond would settle in the molecule throughout the central atom.
This could be one of the top critical points among many behind the absence of lone pairs of electrons in Molecular Geometry. Not only this, according to studies, lone pairs can be found in orbitals where electron bonding is present.
The reason behind occupying more space than electron bonds is that lone pairs are captivated by the nucleus; this concludes that these lone pairs are being spread and functioning near the nucleus with some space.
Valence Shell Electron Pair Repulsion Theory
VSEPR stands for (Valence shell electron pair repulsion); this is the leading mechanism and theory that has proved to be the most helpful factor in the context of determination and prediction of shapes and structural behaviors of the molecule.
Some benefits and critical aspects of the VSEPR charts are that they help with molecular shape prediction. Still, apart from that, it provides electron group identification and electronic structure and assigns AXmEn to the molecules with the identification of bonds and angles.
VSEPR charts also provide three-dimensional molecular geometrical prediction and deep understanding based on the quantity of electron bond pairs and the valence shell of an atom in the molecule. It is widely used for the minimization of repulsion effects along with an auto-arrangement of electron bond pairs.
Electron Geometry
The configuration of pairs of electrons revolving around a central atom is termed electron geometry. It includes the existence of lone pairs and pairs of bonds, as well as the determination of the shape of a molecule in an atom. It is usually specified by the electron pairs.
Types of Electron Geometry
Electron geometry is classified into various types according to electron groups.
Linear Type of Electron Geometry
It involves bonding between the central atom and two electron pairs at 180 degrees of angle, forming a straight-line shape.
Trigonal Planar Type of Electron Geometry
The central atom with three electron pairs at 120-degree angles is termed a trigonal planar arranged in a flat shape.
Tetrahedral Type of Electron Geometry
The central atom is encircled by four pairs of electrons bonding at an angle of 109.5 degrees, arranged in the form of a tetrahedron.
Trigonal Bipyramidal Type of Electron Geometry
A central atom bonds with five pairs of electrons at 120 degrees of angle, forming a trigonal shape with three pairs and 90 degrees of angle with two pairs.
Octahedral Type of Electron Geometry
A central atom with six pairs of bonding electrons forms 90 degrees of an angle. This arrangement gives the shape of two pyramids with an attached square base.
Distinguishing Factors Between Molecular and Electron Geometry
| Features | Molecular Geometry | Electron Geometry |
|---|---|---|
| Basic Concept | Molecular Geometry deals with the understanding and determination of the whole atom and its organization. These atoms are merely present in molecules, and this branch of geometry has all the positioning in 3D. | Whereas Electron Geometry has all the concepts regarding the positioning and organization of numerous electrons. |
| Lone Pairs | In the process of regulating the shape of molecules, this type of geometry keeps lone pairs out. However, lone pairs are considered when repulsion is required in angle and bonding. | While Electron geometry is the opposite of molecule geometry, it does consider not only lone pairs but also bond pairs for the determination of a molecule’s shape. |
| Calculations | It calculates the total quantity of bond pairs of electrons in the process. | It calculates the total quantity of electron pairs in the process. |
| Examples | As an example, we are breaking down H₂O (water) structure; it has O (oxygen) as a central atom in the molecule (along with 6 valence electrons of O), 2 electrons are donated by the hydrogen atom and 8 electrons are surrounding N (nitrogen), 4 electron groups along with 2 lone pairs and single bond pairs in electrons. Moreover, this type is also called Bent. | As an example, we are breaking down CH₄ (Methane); this substance has 4 central atoms in the molecule (along with 4 valence electrons of C (carbon), 4 electrons are donated by the Hydrogen atom and 8 electrons are surrounding C, 4 electron pairs and 4 single bonds are there along with no lone pairs. Further, this type is also called tetrahedral. |
Determination of Shape in Molecule and Electron Geometry
As we have already come to know so far, both are beneficial in their perspectives and conceptual studies. Some steps are concerned with the determination of shapes in both types of geometry, which are important to know about to be aware of the ongoing mechanisms.
For Molecular Geometry
- As mentioned above, lone pairs are not contemplated and reviewed in the process of determining a molecule’s shape, but bonding is still required to keep the function in progress.
- So, single bonds work here for both (double and triple type of bonds, or they both are considered as a single bond)
- In addition, the reason behind the consideration of bond pairs over lone pairs is that lone pairs often take up more space than bond pairs.
- For the determination of an atom’s positions together with the shape of molecules, some geometrical parameters are kept into account, for example, bond angles and lengths, and torsional angles.
- These parameters help in providing significant effects in the form of properties like reactivity, color, polarity, magnetism, etc.
For Electron Geometry
- For shape, the prophecy of an atom in a molecule is important in the way that this prognosticated atom must possess high electron negativity in terms of potential.
- This atom should be central in the molecule, and its configurations, like the number of valence electrons it possesses, should be determined.
- As this is a process, other atoms are supposed to be there, and their donated electron quantity must be calculated.
- Calculate the number of electrons that are neighboring central atoms in a molecule.
- For the determination of the total number of electron groups that are present, we are supposed to subtract the count of total neighboring electrons from (2) so that we can have the required result.
- For the determination of the total count of lone pairs of electrons in the molecule, we need to perform a subtraction of a steric number from the number of single bonds that are present all over the central atom in the molecule.
- Lastly, deep analysis and understanding of electron geometry are required to be determined.
- One additional point to bring to your notice is that there is a chance of similarity in both types of geometry if lone pairs are excluded from the molecule through which central atoms are surrounded.
Conclusion
- Molecular and electron geometry are key branches of geometry.
- The geometry is about how atoms and electron pairs are arranged in molecules.
- Molecular geometry deals with atom arrangement. In contrast, electron geometry focuses on electron pairs around a central atom.
- Lone pairs’ presence distinguishes molecular geometry from electron geometry.
- VSEPR theory predicts molecular shapes based on electron geometry.
- Molecular geometry ignores lone pairs. And Electron geometry considers them.
- Both are vital for understanding chemical properties and molecular structures.
- The understanding of geometry helps in determining molecular shapes. It benefits in many scientific fields.
- Despite differences, both contribute to our grasp of molecular structures and properties.