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In 1999, NASA lost a $125 million Mars orbiter because one engineering team calculated force in imperial pound-seconds while another calculated in metric newton-seconds. A single unstandardized unit sent the entire spacecraft burning up in the Martian atmosphere.
To prevent catastrophic miscommunication, modern science relies on universal rules for units, chemical formulas, and biological names.
How do we write measurements and names so any scientist on Earth interprets them identically?
SI Units and Formatting Conventions
The SI system (Système International d'Unités) defines the standard units of measurement used across all scientific disciplines.
Unit symbols named after a person are capitalized (such as N for Isaac Newton or J for James Joule), whereas general units stay lowercase (such as m for meter or s for second).
📊A visual cheat-sheet card comparing SI unit formatting rules. Left card: 'Case Rules' showing full names written in lowercase ('newton', 'joule', 'celsius') versus single-letter symbols capitalized when named after a scientist ('N', 'J', 'K') and lowercase when not ('m', 's', 'kg'). Right card: 'Spacing & Exponents' showing correct syntax '25.0 cm³' (with space) vs incorrect '25.0cm³' (no space), and derived units written as index notation 'm s⁻¹' or 'g cm⁻³' vs slashed 'm/s'. High-contrast badges with green checkmarks and red crossmarks.
Always leave a single non-breaking space between the numerical value and the unit symbol—write 15.4 g, never 15.4g.
In formal reporting, express compound units using negative index notation, writing velocity as m⋅s−1 and density as g⋅cm−3 rather than using multiple slash symbols.
Standard units solve physical quantities—but what happens when you need to identify an exact chemical substance?
IUPAC Chemical Nomenclature
Before 1919, chemicals went by confusing historical trade names like 'oil of vitriol' or 'muriatic acid.' The IUPAC (International Union of Pure and Applied Chemistry) created systematic naming conventions so that a compound's name directly reflects its molecular structure.
For transition metals that form ions with different charges, the oxidation state (the net positive charge of the metal ion) is written as a Roman numeral in parentheses right after the metal name.