⚗️ Chemistry introductory Lesson 2 of 5 2 min read

Chemical Bonding and Molecular Geometry

How atoms join through ionic, covalent, and hydrogen bonds, and how VSEPR theory predicts the shapes that give molecules their function.

Reading level

What you'll learn

Distinguish ionic, covalent, and hydrogen bonds by how electrons are transferred or shared.
Differentiate polar from nonpolar covalent bonds using electronegativity.
Predict molecular geometry and bond angles from electron domains using VSEPR theory.
Explain why hydrogen bonding is essential to water, DNA, and protein structure.

Types of Chemical Bonds

Ionic Bonds

Ionic bonds form when one atom transfers electrons to another, creating oppositely charged ions that attract electrostatically. Typical between metals and nonmetals (electronegativity difference > ~1.7).

Example: NaCl — Na donates 1 electron to Cl → Na⁺ and Cl⁻.

Covalent Bonds

Electrons are shared between atoms. Occur between nonmetals with similar electronegativities.

Nonpolar covalent — equal sharing (e.g., H₂, O₂)
Polar covalent — unequal sharing → dipole moment (e.g., H₂O, HCl)

Bond order: single (σ) < double (σ+π) < triple (σ+2π). Higher order → shorter, stronger bond.

Hydrogen Bonds

A special dipole–dipole attraction between an H bonded to N, O, or F and a lone pair on another N, O, or F. Weak individually (~20 kJ/mol) but crucial collectively.

Hydrogen bonds govern:

Water’s high boiling point and surface tension
DNA double helix stability (A-T: 2 H-bonds; G-C: 3 H-bonds)
Protein secondary structure (α-helices and β-sheets)

VSEPR Theory

VSEPR (Valence Shell Electron Pair Repulsion) predicts geometry by minimizing electron-pair repulsion.

Electron domains	Geometry	Bond angle	Example
2	Linear	180°	CO₂
3	Trigonal planar	120°	BF₃
4	Tetrahedral	109.5°	CH₄
4 (1 lone pair)	Trigonal pyramidal	~107°	NH₃
4 (2 lone pairs)	Bent	~104.5°	H₂O

Electronegativity and Polarity

Electronegativity (Pauling scale) measures an atom’s ability to attract shared electrons. If two bonded atoms have different electronegativities, the bond is polar — charge is partially shifted toward the more electronegative atom (δ−).

Medical Relevance

Drug-receptor binding relies on intermolecular forces (H-bonds, van der Waals, ionic, and hydrophobic interactions). Understanding polarity helps predict drug solubility, membrane permeability, and bioavailability.

Going deeper advanced

Extra depth for when you're ready — expanded automatically in Advanced mode.

Bond polarity, molecular dipoles, and geometry

A bond's polarity depends on the electronegativity difference between atoms, but a molecule's overall polarity also depends on VSEPR geometry, because bond dipoles add as vectors. Carbon dioxide has two strongly polar C=O bonds yet is nonpolar overall, since its linear shape makes the dipoles cancel; water's bent geometry leaves a net dipole. This distinction predicts solubility and membrane permeability of drugs, since only sufficiently nonpolar or uncharged species cross the lipid bilayer readily.

Hydrogen bonding and the hierarchy of intermolecular forces

Individually weak (roughly 5 to 30 kJ/mol) hydrogen bonds gain their power from cooperativity and number: the same forces that stabilize a protein's alpha-helix and beta-sheet backbone let it fold reproducibly yet unfold during turnover. Beyond hydrogen bonding, London dispersion forces arise from transient induced dipoles and scale with molecular surface area and polarizability, dominating the interactions of nonpolar drug fragments. The balance of these forces, not covalent bonds, governs most reversible receptor binding and protein-ligand recognition.

Key terms

Ionic bond: An electrostatic attraction between oppositely charged ions formed by electron transfer, typically between a metal and a nonmetal.
Covalent bond: A bond in which two atoms share one or more pairs of electrons.
Polar covalent bond: A covalent bond with unequal electron sharing, producing a partial charge separation (dipole).
Hydrogen bond: A weak attraction between a hydrogen bonded to N, O, or F and a lone pair on another electronegative atom.
Electronegativity: An atom's ability to attract shared electrons in a bond, measured on the Pauling scale.
VSEPR theory: A model that predicts molecular shape by arranging electron pairs to minimize repulsion.
Dipole moment: A measure of the separation of positive and negative charge across a bond or molecule.
Bond order: The number of bonding electron pairs shared between two atoms; higher order means shorter, stronger bonds.

Check your understanding

5 questions · answers reveal instantly.

1.Which type of bond forms when one atom transfers electrons to another?
2.According to VSEPR theory, a molecule with four bonding electron domains and no lone pairs (such as CH4) is:
3.Why does water have a bent shape rather than a linear one?
4.A covalent bond between two atoms of very different electronegativity is best described as:
5.Which interaction is primarily responsible for holding the two strands of DNA together?

Citations & References

Links open publicly available educational and peer-reviewed sources.