The Chemistry Book

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A chemical formula is a symbolic way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions. ^[1] As confusing as this may sound, it is actually quite simple. A chemical formula merely a formula that uses element symbols and numbers to represent a compund, polyatomic, etc. The element symbols show what element is used, and the numbers show how many atoms of each element there are.

An example:

CO₂ means one carbon atom to two oxygen atoms.

Counting atoms

A chemical formula is a combonation of elemental symbols and subscript numbers used to show the compostion of a compound. Due to the type of compound the formula represents, the information will vary slightly. ^{CITATION REQUIRED}. One type of compund is an ionic compound, which contains ionic bonds (duh). Thus, you have a nonmetal bonding with a metal, such as NaCl.

Rules for chemical formulas

The rules for writing chemical formulas are pretty basic. Elemental symbol = what element is present. The written subscript, a number, shows how many atoms of that element is present, and goes after the element. When only one atom of an element if found the subscript 1 is not written. ^[2] For instance, take H₂O. The two is a subscript and is after the H, so you know that a water molecule has two hydrogen atoms and one oxygen atom.

TIPS to Keep In Mind

• Use correct case for element symbols. If correct case is not used, the formula may be ambiguous and the interpretation chosen may not be the desired one. (example: Au and AU are not the same. -.-)
• The metal always goes before the nonmetal(s)
• If only one atom of an atom is there, you don't have to write a subscript 1 after the element symbol.
• Parentheses may be used to group polyatomics.
• The amount of the same element can be added. (example: CH₃ (CH₂ ) 4CH₃ could be also written as C₆H₁₄. )
• A regular-sized number in FRONT of a molecule/compound/etc. means there's that amount of the WHOLE THING (example: 4CH₃, with 4 as a regular-sized number and the three as a subscript, that means there's 4 carbons (4x1=4) and 12 hydrogens (4x3=12))
• To explicitly specify an ion, place the charge at the end of the formula. If the charge is greater than one the charge should be included after the + or - symbol (e.g., Li⁺² ).

Formulas

The empirical formula of a chemical compound is a simple expression of the relative number of each type of atom in it.This formula is known as the simplest formula of a compound that expresses the smallest whole number ratio of the atoms present.^{CITATION REQUIRED}. The actual formula of a compound, the one that gives the composition that are represented are called molecular formulas.^{CITATION REQUIRED}. There are other methods for writing out this formula as well. Chemical formulas such as HClO4 can be divided into empirical formula, molecular formula, and structural formula.^[3] The formula H2O is also the molecular formula of water. For non-molecular substances such as table salt, we represent the composition with an empirical formula.^[4] Ionic compounds are formed by two ions of opposite charges and are held together by a relatively weak attraction also know as a formula unit. NaCl is the chemical formula for the compound table salt. ^[5]

References