formula weight: meaning, definition, pronunciation and examples
C1Technical/Scientific
Quick answer
What does “formula weight” mean?
The sum of the atomic weights of all atoms in a chemical formula, expressed in atomic mass units (amu).
Audio
Pronunciation
Definition
Meaning and Definition
The sum of the atomic weights of all atoms in a chemical formula, expressed in atomic mass units (amu).
In chemistry, the calculated mass of a molecule or formula unit based on the standard atomic weights of its constituent elements. It is numerically equivalent to molecular weight for covalent compounds but is used for ionic compounds and other substances without discrete molecules.
Dialectal Variation
British vs American Usage
Differences
No significant difference in meaning or usage. Spelling follows regional conventions (e.g., 'formulae' as plural is slightly more common in UK English, but 'formulas' is standard for this compound term in both).
Connotations
Identical technical connotations in both varieties.
Frequency
Equally frequent in academic and technical chemistry contexts in both regions.
Grammar
How to Use “formula weight” in a Sentence
The formula weight of [compound] is [number].To find the formula weight, sum the atomic masses.[Compound] has a formula weight of [number].Vocabulary
Collocations
Examples
Examples of “formula weight” in a Sentence
verb
British English
- n/a
American English
- n/a
adverb
British English
- n/a
American English
- n/a
adjective
British English
- n/a
American English
- n/a
Usage
Meaning in Context
Business
Not used.
Academic
Core term in introductory and analytical chemistry courses and textbooks.
Everyday
Virtually never used outside scientific contexts.
Technical
Essential term in chemical calculations, stoichiometry, and analytical reports.
Vocabulary
Synonyms of “formula weight”
Strong
Neutral
Weak
Vocabulary
Antonyms of “formula weight”
Watch out
Common Mistakes When Using “formula weight”
- Using 'formula weight' for a single element (use 'atomic weight').
- Confusing it with 'molar mass' (which has units of g/mol).
- Misspelling as 'formular weight'.
FAQ
Frequently Asked Questions
They are often used interchangeably, but strictly, 'molecular weight' refers to the mass of a discrete covalent molecule, while 'formula weight' is used for ionic compounds (like salts) which do not exist as individual molecules.
Formula weight is expressed in atomic mass units (amu or u). When this number is expressed in grams per mole (g/mol), it is called molar mass.
Multiply the atomic weight of each element in the formula by the number of atoms of that element, then sum all the values.
Yes, because atomic weights of elements are averages based on isotopic abundance, so calculated formula weights often have decimals (e.g., the formula weight of NaCl is approximately 58.44 amu).
The sum of the atomic weights of all atoms in a chemical formula, expressed in atomic mass units (amu).
Formula weight is usually technical/scientific in register.
Formula weight: in British English it is pronounced /ˈfɔːmjʊlə weɪt/, and in American English it is pronounced /ˈfɔːrmjələ weɪt/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “n/a”
Learning
Memory Aids
Mnemonic
Think of a 'formula' as a recipe. The 'formula weight' is the total weight of all ingredients (atoms) listed in that recipe.
Conceptual Metaphor
WEIGHT AS A SUM (The total is conceptualized as a weight accumulated by adding parts).
Practice
Quiz
For which of the following is 'formula weight' the most precise term to use?