Calculate molar mass, elemental composition, and mass percentages instantly
Enter a valid chemical formula. Case sensitive (e.g., 'Co' is Cobalt, 'CO' is Carbon Monoxide).
Invalid chemical formula format.
— Select a Compound —
Water (H2O)
Carbon Dioxide (CO2)
Sodium Chloride (NaCl)
Glucose (C6H12O6)
Ethanol (C2H5OH)
Sulfuric Acid (H2SO4)
Caffeine (C8H10N4O2)
Baking Soda (NaHCO3)
Total Molecular Weight (Molar Mass)
180.156
g/mol
24
Total Atoms
3
Unique Elements
O
Heaviest Component
Elemental Breakdown
Element
Atom Count
Atomic Mass (g/mol)
Total Mass (g/mol)
Mass %
What is a Periodic Table Molecular Weight Calculator?
A periodic table molecular weight calculator is an essential tool for chemists, students, and researchers designed to compute the total mass of a chemical compound based on its formula. By referencing the atomic weights of individual elements from the periodic table, this calculator determines the molar mass—defined as the mass of one mole of a substance, typically expressed in grams per mole (g/mol).
Whether you are balancing stoichiometric equations in a lab or calculating the dosage for a pharmaceutical solution, understanding the precise molecular weight is critical. This tool eliminates the need for manual lookups and tedious addition, ensuring accuracy in your chemical calculations.
Common misconceptions include confusing molecular weight (mass of a single molecule in Daltons) with molar mass (mass of a mole in grams). While numerically identical for practical purposes, their units differ. This calculator provides the standard molar mass used in most laboratory settings.
Molecular Weight Formula and Mathematical Explanation
The calculation of molecular weight follows the principle of summation of atomic masses. The formula is derived by summing the product of the atomic mass of each element and the number of atoms of that element present in the molecule.
The General Formula
MW = Σ (ni × Ai)
Where:
MW = Total Molecular Weight (g/mol)
ni = Number of atoms of element i
Ai = Standard Atomic Weight of element i
Variable
Meaning
Unit
Typical Range
Atomic Weight
Average mass of an atom
u or g/mol
1.008 (H) to 294 (Og)
Subscript
Quantity of atoms
Integer
1 to 1000+ (polymers)
Molar Mass
Mass per mole of substance
g/mol
2.016 to 100,000+
Practical Examples (Real-World Use Cases)
Example 1: Glucose (C6H12O6)
Glucose is a simple sugar and a vital energy source. To find its molecular weight:
Interpretation: If you need 1 mole of glucose for a reaction, you would weigh out exactly 180.156 grams.
Example 2: Calcium Hydroxide (Ca(OH)2)
Used in sewage treatment and food processing. Note the parentheses indicating the hydroxide group is doubled.
Calcium (Ca): 40.078 × 1 = 40.078
Oxygen (O): 15.999 × 2 = 31.998
Hydrogen (H): 1.008 × 2 = 2.016
Total: 40.078 + 31.998 + 2.016 = 74.092 g/mol
How to Use This Periodic Table Molecular Weight Calculator
Enter the Formula: Type the chemical formula into the input field. Use standard notation (e.g., NaHCO3).
Case Sensitivity: Ensure you use uppercase for the first letter of an element and lowercase for the second (if applicable). For example, use "Cl" for Chlorine, not "cl" or "CL".
Handle Groups: Use parentheses for groups like nitrates or hydroxides, e.g., Mg(NO3)2.
Review Results: The calculator instantly updates the total mass, atom count, and provides a visual breakdown of the mass percentage.
Analyze Composition: Use the table to see which element contributes most to the total mass—crucial for gravimetric analysis.
Key Factors That Affect Molecular Weight Results
While the calculation is mathematical, several physical factors influence the interpretation and application of molecular weight data:
Isotopic Variation: Standard atomic weights are averages based on natural abundance. If you are working with isotopically enriched samples (e.g., Carbon-13), the standard weight will be inaccurate.
Hydration State: Many compounds absorb water from the air. Copper Sulfate (CuSO4) has a different weight than Copper Sulfate Pentahydrate (CuSO4·5H2O). Always account for water molecules.
Purity of Sample: In practical applications, reagents are rarely 100% pure. Impurities affect the effective molar mass needed for stoichiometric calculations.
Precision of Atomic Weights: The IUPAC periodically updates atomic weights. This calculator uses standard values to 3-4 decimal places, which is sufficient for most analytical chemistry but may differ slightly from ultra-high precision physics data.
Polymerization: For polymers, the formula represents a monomer. The actual molecular weight is a distribution average (Mn or Mw) rather than a single fixed number.
Experimental Error: When comparing calculated weight to experimental mass spectrometry data, remember that mass specs often measure the most abundant isotope mass, not the average atomic mass.
Frequently Asked Questions (FAQ)
Does this calculator handle hydrates?
Yes, but you must enter them as part of the formula. For example, for CuSO4·5H2O, you can enter it as CuSO4(H2O)5 to get the correct total mass.
Why is the result different from my textbook?
Small discrepancies often arise from rounding differences in atomic weights. This calculator uses high-precision values (e.g., H = 1.008), whereas some textbooks round to H = 1.01 or 1.0.
Can I calculate the weight of an ion?
Yes. The mass of an electron is negligible compared to protons and neutrons. Therefore, the molar mass of SO42- is effectively the same as the neutral SO4 group for most stoichiometric purposes.
What is the difference between molecular weight and molar mass?
Molecular weight is the mass of one molecule (measured in amu or Daltons). Molar mass is the mass of one mole of substance (measured in g/mol). Numerically, they are the same.
How do I enter organic chains?
You can enter condensed formulas like CH3CH2OH or molecular formulas like C2H6O. Both will yield the same correct molecular weight.
Does the calculator support all 118 elements?
Yes, the calculator includes atomic data for elements from Hydrogen (1) to Oganesson (118).
Why is case sensitivity important?
Chemistry symbols rely on case to distinguish elements. "Co" is Cobalt, while "CO" is Carbon and Oxygen. Incorrect casing will lead to calculation errors.
Is this tool suitable for pharmaceutical calculations?
Yes, it provides the precision necessary for general pharmaceutical compounding and molarity calculations.