A short Note on Linear Shape of Molecule

In chemistry, linear molecular geometry refers to the shape of a molecule that revolves around a centre atom connected to two additional atoms (or ligands) at an angle of 180 degrees. The carbon centres of linear organic compounds like acetylene (HC Ξ CH) are frequently explained using sp orbital hybridization.

Linear Shape Molecules

Linear shape molecules: Linear geometry occurs at centre atoms with two linked atoms and zero or three lone pairs (AX₂ or AX₂E₃) in the AXE notation, according to the VSEPR model (Valence Shell Electron Pair Repulsion model). Beryllium fluoride (F-Be-F) with two single bonds, carbon dioxide (O=C=O) with two double bonds, and hydrogen cyanide (HCN) with one single and one triple bond are examples of neutral AX₂ molecules with linear geometry. Acetylene (HC Ξ CH) is the most important linear molecule with more than three atoms, with each of its carbon atoms acting as a core atom with a single hydrogen bond and a triple connection to the other carbon atom. Azide (N₃^–) and thiocyanate (SCN^–) are linear anions, and the nitronium ion (NO₂⁺) is a linear cation.

Valence Shell

The valence shell is the outermost shell of each atom, and the electrons that reside in it are known as valence electrons. When the valence electrons in any atom receive enough energy from an external force, they can break away from the parent atom and become free electrons. The outermost shell of the copper atom seen below has only one electron, indicating that it has only one valence electron.

Valence-Shell Electron-Pair Repulsion Theory (VSEPR)

To minimize electron-electron repulsion, pairs of electrons surrounding the core atom , The Valence Shell Electron Pair Repulsion (VSEPR) theory states that a molecule or ion should be as far away as possible.

By following a basic approach, this simple principle may be utilised to predict the shapes of molecules:

• Decide which atom in a molecule is the center atom.

(If in doubt, choose the least electronegative atom because it will  be better equipped to share electrons with the other atoms in the molecule.)

• On the centre atom, add up the valence (outer shell) electrons .
• Count how many electrons the outside atoms utilised to form bonds with the central atom .
• The count of Valence Shell Electron Pairs (VSEP) is equal to the sum of (2) + (3) divided by two.
• The number of VSEP determines the molecule’s expected shape .

Linear Molecules List

1. CO₂ : CO₂ is linear because there are no lone pairs on the C atom that would cause the bond angle to decrease. In CO₂, the bond angle of O-C-O is 180^o .
2. XeF₂ :The electron configuration is a trigonal bipyramidal , Because lone pairs prefer equatorial locations, the form is linear. XeF₂ has three lone pairs and two bond pairs.
3. BeH₂ : Because the beryllium atom in the centre has two Be-H bonds with the two hydrogen atoms on either side. In linear geometry, the H-Be-H bond creates a 180-degree angle. Because it includes two hydrogen atoms, the BeH₂ molecule has a linear form. 

Determine If The Molecule Is Linear By Looking At The VSEPR Theory

Simply remember that lone pairs reject one another. Lone pairs are electrons with a negative charge, and because negative and negative charges repel one another (while positive charges attract negative charges), they repel each other. In other words, unpaired electrons will want to go as far away from each other as feasible.So, if we get a compound for example BeH₂ that is not having any lone pairs of electrons , it will develop into a linear compound because the hydrogens will oppose each other as much as possible to form a straight line. In contrast to other compounds, BeF₂ has lone pairs of electrons on the fluorines , 6 electrons apiece. Because an equal number of lone pairs of electrons reject each other so aggressively, the farthest they may be from each other is when the molecule rests at 180 degrees, this compound remains linear. The majority of molecules, such as Co₂ and Scl₂, are linear . There are a few exceptions to this rule. Another way to look at it is from the bottom up. Take, for instance, water. Despite the fact that H₂O appears to be linear, it is not. Because oxygen has eight electrons and the two hydrogens only have four, there are two pairs of lone electrons (or 4 electrons left). Because electrons oppose each other, water will have a tetrahedral bent structure rather than a linear shape.

Linear Shape Molecules Examples

BeCl₂ , AX₂E₃ , CO₂ , XeF₂  etc.

Conclusion

The molecular shape or molecular geometry is defined by the placement of each atom’s nucleus in three-dimensional space. Molecular shapes are significant in predicting how one molecule will react with another and defining macroscopic features like melting and boiling points.