Molecular masses that are twice the atomic mass generally occur when a molecule consists of two atoms of the same element. In such cases, the molecular mass is equal to twice the atomic mass of the element.
For example:
Oxygen (O2): The molecular mass of oxygen (O2) is approximately 32 atomic mass units (amu), which is twice the atomic mass of oxygen (16 amu). Each oxygen molecule (O2) consists of two oxygen atoms.
Nitrogen (N2): The molecular mass of nitrogen (N2) is approximately 28 amu, which is twice the atomic mass of nitrogen (14 amu). Nitrogen gas (N2) is made up of two nitrogen atoms.
This pattern generally applies to diatomic molecules composed of the same element. It's worth noting that molecular masses can vary for molecules that contain different elements or have more complex structures.