Use subscript for numbers in formulas
Type the formula normally, such as H2O
Highlight the number you want to make subscript
Click Format
Select Text
Click Subscript
Use the keyboard shortcut Ctrl+, on Windows or Cmd+, on Mac
Repeat for each number that should be subscript
Use superscript for charges or exponents when needed
Highlight the character you want to make superscript
Click Format
Select Text
Click Superscript
Use the keyboard shortcut Ctrl+. on Windows or Cmd+. on Mac
Use the equation editor for more complex chemical notation
Click Insert
Select Equation
Type the chemical expression using equation formatting
Use special characters if needed from the Insert menu
Copy and paste formulas from another source if formatting is already correct