def atom_mass(atom, coef=0.01):
    """Get the mass of an atom and scale it.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    coef : float
        The mass will be multiplied by ``coef``.

    Returns
    -------
    list
        List containing one float only.
    """
    return [atom.GetMass() * coef]
