```python
- A dictionary of some common elements and their relative atomic masses
elements = {'H': 1.008, 'He': 4.003, 'Li': 6.941, 'Be': 9.012,
'B': 10.81, 'C': 12.01, 'N': 14.01, 'O': 16.00,
'F': 19.00, 'Ne': 20.18, 'Na': 22.99, 'Mg': 24.31,
'Al': 26.98, 'Si': 28.09, 'P': 30.97, 'S': 32.07,
'Cl': 35.45, 'K': 39.10, 'Ar': 39.95, 'Ca': 40.08,
'Sc': 44.96, 'Ti': 47.87, 'V': 50.94, 'Cr': 52.00,
'Mn': 54.94, 'Fe': 55.85, 'Ni': 58.69, 'Co': 58.93,
'Cu': 63.55, 'Zn': 65.38, 'Ga': 69.72, 'Ge': 72.63,
'As': 74.92, 'Se': 78.96, 'Br': 79.90, 'Kr': 83.80,
'Rb': 85.47, 'Sr': 87.62, 'Y': 88.91, 'Zr': 91.22,
'Nb': 92.91, 'Mo': 95.94, 'Tc': 98.00, 'Ru': 101.1,
'Rh': 102.9, 'Pd': 106.4, 'Ag': 107.9, 'Cd': 112.4,
'In': 114.8, 'Sn': 118.7, 'Sb': 121.8, 'I': 126.9,
'Te': 127.6, 'Xe': 131.3, 'Cs': 132.9, 'Ba': 137.3,
'La': 138.9, 'Ce': 140.1, 'Pr': 140.9, 'Nd': 144.2,
'Pm': 145.0, 'Sm': 150.4, 'Eu': 152.0, 'Gd': 157.3,
'Tb': 158.9, 'Dy': 162.5, 'Ho': 164.9, 'Er': 167.3,
'Tm': 168.9, 'Yb': 173.0, 'Lu': 175.0, 'Hf': 178.5,
'Ta': 180.9, 'W': 183.8, 'Re': 186.2, 'Os': 190.2,
'Ir': 192.2, 'Pt': 195.1, 'Au': 197.0, 'Hg': 200.6,
'Tl': 204.4, 'Pb': 207.2, 'Bi': 208.9, 'Th': 232.0,
'Pa': 231.0, 'U': 238.0, 'Np': 237.0, 'Pu': 244.0,
'Am': 243.0, 'Cm': 247.0, 'Bk': 247.0, 'Cf': 251.0,
'Es': 252.0, 'Fm': 257.0, 'Md': 258.0, 'No': 259.0,
'Lr': 262.0, 'Rf': 267.0, 'Db': 270.0, 'Sg': 271.0,
'Bh': 270.0, 'Hs': 277.0, 'Mt': 276.0, 'Ds': 281.0,
'Rg': 280.0, 'Cn': 285.0, 'Nh': 284.0, 'Fl': 289.0,
'Mc': 288.0, 'Lv': 293.0}
- A function to calculate the relative molecular mass of a chemical formula
def calculate_rmm(formula):
# Initialize the result to zero
result = 0
# Initialize an empty string to store the current element symbol
element = ""
# Initialize an empty string to store the current number of atoms
number = ""
# Initialize an empty list to store the stack of parentheses
stack = []
# Loop through each character in the formula
for char in formula:
# If the character is an uppercase letter
if char.isupper():
# If there is a previous element symbol
if element:
# If there is a previous number of atoms
if number:
# Convert the number to an integer and multiply it by the relative atomic mass of the element
value = int(number) * elements[element]
else:
# Otherwise assume the number is one and multiply it by the relative atomic mass of the element
value = elements[element]
# If there is a stack of parentheses
if stack:
# Append the value to the stack
stack.append(value)
else:
# Otherwise add it to the result
result += value
# Reset the number to an empty string
number = ""
# Set the current element symbol to the character
element = char
# If the character is a lowercase letter
elif char.islower():
# Append it to the current element symbol
element += char
elif char.isdigit():
number += char
elif char == "(":
if element:
if number:
value = int(number) * elements[element]
else:
value = elements[element]
if stack:
stack.append(value)
else:
result += value
element = ""
number = ""
stack.append(char)
elif char == ")":
if element:
if number:
value = int(number) * elements[element]
else:
value = elements[element]
if stack:
stack.append(value)
else:
result += value
element = ""
number = ""
# Pop the values from the stack until reaching a left parenthesis
temp_result = 0
while stack and stack[-1] != "(":
temp_result += stack.pop()
# Pop the left parenthesis from the stack
if stack and stack[-1] == "(":
stack.pop()
# Check if there is a number after the right parenthesis
i = formula.index(char) + 1
if i < len(formula) and formula[i].isdigit():
# Multiply the temporary result by the number and append it to the stack or add it to the result
temp_result *= int(formula[i])
if stack:
stack.append(temp_result)
else:
result += temp_result
# Skip the next character as it is already processed
continue
else:
# Otherwise append the temporary result to the stack or add it to the result as it is
if stack:
stack.append(temp_result)
else:
result += temp_result
# Check if there is a remaining element and number at the end of the formula and add them to the result
if element:
if number:
value = int(number) * elements[element]
else:
value = elements[element]
result += value
return result
- Ask for user input and print out the result or error message
def main():
while True:
try:
formula = input("Enter a chemical formula: ")
rmm = calculate_rmm(formula)
print("The relative molecular mass of {} is {:.3f}".format(formula,rmm))
except KeyError as e:
print("Unknown element: {}".format(e))
except ValueError as e:
print(e)
if __name__ == "__main__":
main()
```