Which has highest boiling point

Answer: H₂O is the polar molecule.

Boiling point order:
H₂S < H₂Se < H₂Te < H₂O

Why H₂O is a polar molecule: An Explanation

When determining molecular polarity, chemists focus on two key factors: bond polarity and molecular geometry. A molecule is polar if it has polar bonds and an asymmetric shape that produces a net dipole moment.

Step 1: Check bond polarity

Bond polarity arises from differences in electronegativity between atoms. Oxygen is much more electronegative than hydrogen, so the O–H bonds in H₂O are polar covalent bonds, with oxygen pulling electron density toward itself.

Step 2: Examine molecular shape

Using VSEPR theory (Valence Shell Electron Pair Repulsion), the shape of each molecule can be predicted:

• CO₂ – Linear molecule. The two C=O bond dipoles point in opposite directions and cancel out. Result: nonpolar.

• CH₄ – Tetrahedral and perfectly symmetrical. Even though C–H bonds have slight polarity, their dipoles cancel. Result: nonpolar.

• BF₃ – Trigonal planar and symmetrical. The three B–F bond dipoles cancel each other. Result: nonpolar.

• H₂O – Bent (V-shaped) due to two lone pairs on oxygen. The O–H bond dipoles do not cancel, creating a net dipole toward oxygen. Result: polar.

Why this matters in chemistry

The polarity of water explains many of its important properties, such as hydrogen bonding, high boiling point, and excellent ability to dissolve ionic and polar substances. This is why water is often called the “universal solvent.”