What ₂ means
In H₂O, the lowered 2 marks two hydrogen atoms. It attaches a count to the element symbol just before it; alone, ₂ has no fixed reading.
Swedish chemist Jöns Jacob Berzelius used raised atom counts in formulas in the 19th century; modern formulas place them below element symbols. Raised and lowered characters also serve phonetic transcription (writing speech sounds with symbols), databases, and plain-text exchange. Use formatting for full expressions.
Don't confuse it with
1Combination ideas
2Water's formula: two hydrogen atoms and one oxygen atom.
Carbon dioxide's formula: one carbon atom and two oxygen atoms.
Questions people ask
1Why does ₂ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ₂
Windows (Word)
Alt+XType 2082, then Alt+X to get ₂.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “subscript two”.
Linux
Ctrl+Shift+UType 2082, then Enter or Space.
HTML
₂CSS
\2082HTML
In HTML, use `₂` for this character or `<sub>2</sub>` to style a 2 below the line.
Codes and encoding1 code points
HTML decimal
₂
HTML hex
₂
CSS content
content: "\2082";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%82%82
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.