def __charge_to_sdf(charge):
    """Translate RDkit charge to the SDF language.

    Args:
        charge (int): Numerical atom charge.

    Returns:
        str: Str representation of a charge in the sdf language
    """
    if charge == -3:
        return "7"
    elif charge == -2:
        return "6"
    elif charge == -1:
        return "5"
    elif charge == 0:
        return "0"
    elif charge == 1:
        return "+1"
    elif charge == 2:
        return "+2"
    elif charge == 3:
        return "+4"
    else:
        return "0"