Chemical elements have both a full name, such as “oxygen,” and a corresponding symbol, like “O.” This distinction often causes confusion regarding capitalization, as the rules for names are distinct from the rules for symbols. Understanding the proper conventions for writing element names versus their symbols is important for clarity when discussing scientific concepts. These standards are established by the scientific community for the 118 known chemical elements.
Capitalization Rules for Element Names
The written names of chemical elements are treated as common nouns in the English language, meaning they are generally not capitalized within a sentence. This convention applies regardless of whether the element name is derived from a place, a person, or a mythological figure, such as uranium, curium, or titanium. For instance, one would write, “The atmosphere contains nitrogen and oxygen,” using lowercase letters for both element names.
The International Union of Pure and Applied Chemistry (IUPAC) confirms that element names are common nouns and should be written in lowercase. The primary exception is the standard grammar requirement that the first word of any sentence must be capitalized. Therefore, the element name is capitalized only when it begins a sentence, such as in the statement, “Neon is a noble gas used in certain types of lighting.”
Capitalization may also occur if the element name is incorporated into a proper noun, such as the name of a company or a registered trademark. This rule also applies to element names that are part of a larger chemical compound or isotope name, such as “carbon-14” or “sodium chloride,” where the element name itself remains uncapitalized.
Capitalization Rules for Chemical Symbols
In contrast to the full names, the abbreviations used to represent elements—known as chemical symbols—adhere to a strict set of capitalization guidelines. The chemical symbol for every element must always begin with a capital letter, regardless of its position within a sentence or a chemical formula. This standardized notation is universally applied to ensure instant recognition of the element.
For elements with a single-letter symbol, such as hydrogen (H), carbon (C), or fluorine (F), the letter is always capitalized. When the symbol consists of two letters, the first letter is capitalized, and the second letter is always written in lowercase. Examples of this two-letter convention include iron (Fe), cobalt (Co), and aluminum (Al).
This rule of capitalization for symbols is essential for reading chemical formulas correctly, as the capital letter signals the start of a distinct element. For example, the symbol for carbon monoxide is CO, signifying one atom of carbon and one atom of oxygen. If the symbol were written as Co, it would instead represent a single atom of the element cobalt.