@staticmethod
def is_apolar(a):
    """
        returns true if a given atom is a apolar

        :param a: a `ccdc.molecule.Atom` instance
        :return: bool, true if the atom classification is "apolar"
        """
    if (a.is_donor or a.is_acceptor or a.formal_charge != 0 or a.
        atomic_symbol == 'Xe'):
        return False
    else:
        return True
