# 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, "Ar": 39.95, "K": 39.10 , "Ca" :40.08 ,
'Sc':44.96 , 'Ti':47.87 , 'V':50.94 , 'Cr':52.00 ,
'Mn':54.94 , 'Fe':55.85 , 'Co':58.93 , 'Ni':58.69 ,
'Cu':63.55 , 'Zn':65.38 , 'Ga':69.72 , 'Ge':72.63 ,
'As':74.92 , 'Se':78.97 , 'Br':79.90 , 'Kr' :83.80 ,
'Rb' :85.47 ,'Sr' :87.62,'Y' :88.91,'Zr':91.22,
'Nb' :92.91,'Mo' :95.95,'Tc' :98 ,'Ru' :101.07,
'Rh' :102.91,'Pd' :106.42,'Ag' :107.87,'Cd' :112.41,
'In' :114.82,'Sn' :118.71,'Sb' :121.76,'Te' :127.60,
'I':126.90,'Xe':131.29,'Cs':132.91,'Ba':137.33,
'Hf':178.49,'Ta':180.95,'W':183.84,
'Ir':192.22,'Pt':195.08,'Au':196.97,
'Pb':207.2,'Bi':208.98}
# 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()