import re


def check_molecule(molecule):
    """
    Check if the given string is a molecule

    Parameters
    ----------
    molecule : String
        Molecular formula.

    Returns
    -------
    True if the given string is a molecule, false otherwise (if it is an atom).

    """
    match = re.match('^[A-Z]{1}[a-z]?$', molecule)     # Matches a string containing only 1 capital letter followed by 0 or 1 lower case letters
    
    if match: return False   # If our 'molecule' matches the pattern, it is really an atom
    else: return True        # We did not get a match, therefore must have a molecule