Chemical bonding and molecular structure form the backbone of chemistry, especially for students preparing for competitive exams like NEET. This topic explains why atoms combine, how molecules are formed, and why different substances show different physical and chemical properties. From simple salt crystals to complex molecules like ammonia or benzene, everything depends on how atoms bond and arrange themselves in space. This article explains the concepts exactly as covered in the uploaded PDF, keeping the language simple and exam-focused.
I am writing this article because many students struggle with this chapter despite it being scoring. The concepts are logical, but they often feel confusing due to multiple theories, rules, and exceptions. Once these ideas are understood step by step, questions from this chapter become predictable. This explanation sticks strictly to the content of the uploaded PDF and presents it in a clean, connected manner so learners can revise confidently without jumping between multiple sources.
What Is a Chemical Bond
A chemical bond is the force that holds atoms or ions together in a molecule or compound. According to the PDF, atoms bond to achieve a more stable electronic configuration. This stability usually comes from completing the octet in the valence shell, though there are exceptions like hydrogen and boron. Chemical bonds explain why substances exist as solids, liquids, or gases and why they show specific reactivity patterns.
Ionic and Covalent Bonding
Ionic bonding occurs due to the transfer of electrons from a metal to a non-metal, forming oppositely charged ions that attract each other. These compounds generally have high melting and boiling points, conduct electricity in molten or dissolved state, and are hard and brittle.
Covalent bonding, on the other hand, involves sharing of electrons between atoms. Covalent compounds usually have low melting points, poor electrical conductivity, and exist as gases or liquids. Depending on the number of shared electrons, covalent bonds can be single, double, or triple. The PDF clearly contrasts these properties with suitable examples.
Coordinate Bond and Bond Parameters
A coordinate bond is a special type of covalent bond where both shared electrons are donated by one atom. This concept is important for understanding molecules like ammonium ion.
The PDF also explains bond length, bond angle, bond energy, and bond order. With increase in bond order, bond length decreases and bond energy increases. These relationships are commonly tested in NEET questions and are essential for comparing molecular stability.
Polar and Non-Polar Covalent Bonds
Non-polar covalent bonds form when atoms of the same element share electrons equally. Polar covalent bonds form when there is a difference in electronegativity, leading to partial positive and negative charges.
Dipole moment is used to measure polarity. The PDF explains that even molecules with polar bonds can be non-polar overall if their geometry is symmetrical, like CO₂ or BF₃. This idea is crucial for eliminating wrong options in multiple-choice questions.
Valence Bond Theory and Overlapping
According to Valence Bond Theory, a covalent bond forms by the overlap of half-filled atomic orbitals. Greater the overlap, stronger is the bond. Sigma bonds are formed by head-on overlap, while pi bonds are formed by sidewise overlap.
Sigma bonds are stronger than pi bonds and allow free rotation, while pi bonds restrict rotation. The PDF uses clear orbital diagrams to explain this difference, which is very helpful for conceptual clarity.
Download this CHEMICAL BONDING & MOLECULAR STRUCTURE PDF: Click Here
Hybridisation and Molecular Geometry
Hybridisation explains how atomic orbitals mix to form equivalent hybrid orbitals. The type of hybridisation decides the shape of the molecule.
The PDF covers sp, sp², sp³, dsp², sp³d, and sp³d² hybridisations with examples like BeCl₂, BF₃, CH₄, PCl₅, and SF₆. It also explains how lone pairs distort ideal geometry, leading to shapes like bent, trigonal pyramidal, T-shaped, and square planar.
VSEPR Theory and Lone Pair Repulsion
VSEPR theory states that electron pairs repel each other and arrange themselves to minimise repulsion. Lone pair–lone pair repulsion is the strongest, followed by lone pair–bond pair, and then bond pair–bond pair.
This explains why bond angles decrease from CH₄ to NH₃ to H₂O. The PDF provides several tables showing shapes of molecules with and without lone pairs, which are extremely useful for quick revision.
Molecular Orbital Theory
Molecular Orbital Theory treats electrons as belonging to the entire molecule rather than individual bonds. Atomic orbitals combine to form bonding and antibonding molecular orbitals.
Bond order is calculated using this theory and helps predict stability. The PDF explains why molecules like He₂ do not exist and why O₂ is paramagnetic, both of which are classic NEET questions.
Hydrogen Bonding
Hydrogen bonding is an attractive force between hydrogen and highly electronegative atoms like oxygen, nitrogen, or fluorine. It can be intermolecular or intramolecular.
This bonding explains high boiling points of water and alcohols and special structures like ortho-nitrophenol. The PDF highlights how hydrogen bonding affects physical properties rather than forming true chemical bonds.
