1. The molecule has a symmetrical shape. This means that the distribution of electrons is equal throughout the molecule, resulting in no overall dipole moment.

2. The molecule is composed of atoms with similar electronegativity. Electronegativity is the tendency of an atom to attract electrons. When atoms have similar electronegativity, they share electrons equally in a covalent bond. This creates a balanced distribution of electrons and, therefore, no dipole moment.

Examples:

* CO2 (carbon dioxide): The linear shape of CO2 and the similar electronegativity of carbon and oxygen atoms result in a nonpolar molecule.

* CH4 (methane): The tetrahedral shape of methane and the similar electronegativity of carbon and hydrogen atoms result in a nonpolar molecule.

* O2 (oxygen gas): The diatomic oxygen molecule has a symmetrical shape and the two oxygen atoms have equal electronegativity. This makes it nonpolar.

In contrast, polar molecules:

* Have an asymmetrical shape.

* Have a difference in electronegativity between the atoms involved in the molecule.

Note: Some molecules can be polar even if they have a symmetrical shape if the atoms involved have a significant difference in electronegativity. This creates a dipole moment within the molecule, even if the overall shape is symmetrical.