def atomic_number(atom):
    """Get the atomic number for an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
       List containing one int only.

    See Also
    --------
    atomic_number_one_hot
    atom_type_one_hot
    """
    return [atom.GetAtomicNum()]
