Definition of Chemical Formula
A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas, and plus (+) and minus (−) signs.
These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words.
Here are some more definitions of Chemical Formula:
Although a chemical formula may imply certain simple chemical structures. It is not the same as a full chemical structural formula.
Chemical formulae can fully specify the structure of only the simplest of molecules and chemical substances and are generally more limited in power than chemical names and structural formulae.
A chemical formula is any of several kinds of expressions of the composition or structure of chemical compounds. The forms commonly encountered are empirical, molecular, structural, and projection formulas.
An empirical formula consists of symbols representing elements in a compound, such as Na for sodium and Cl for chlorine, and subscripts indicating each constituent element’s relative number of atoms.
A subscript is not used, however, unless the number is more than one. Thus, benzene is represented by the empirical formula CH. Which indicates that a typical compound sample contains one atom of carbon (C) to one atom of hydrogen (H).
Water is represented by the empirical formula H2O, denoting that the substance contains two atoms of hydrogen (H2) for every atom of oxygen (O).
A chemical formula is a notation used by scientists to show the number and type of atoms present in a molecule, using atomic symbols and numerical subscripts.
Chemical formula is a simple representation, in writing, of a three-dimensional molecule that exists. A chemical formula describes a substance, down to the exact atoms which make it up.
There are three basic types of chemical formula, the empirical formula, the molecular formula, and the structural formula.
When the chemical compound of the formula consists of simple molecules, chemical formulae often employ ways to suggest the molecule’s structure.
These types of formulae are variously known as molecular formulae and condensed formulae. A molecular formula enumerates the number of atoms to reflect those in the molecule.
The molecular formula for glucose is C6H12O6 rather than the glucose’s empirical formula, which is CH2O.
However, except for elementary substances, molecular chemical formulae lack needed structural information and are ambiguous.
Types of Chemical Formula
There are three basic types of chemical formula, the empirical formula, the molecular formula, and the structural formula:
1. Empirical Formula
- The empirical chemical formula represents the relative number of atoms of each element in the compound. Some compounds, like water, have the same empirical and molecular formula because they are small and have the same ratio of atoms in molecules and the number of atoms in a molecule. The empirical and molecular formula for water looks like this: H2O.
- The empirical formula is determined by the weight of each atom within the molecule. Therefore, for a slightly bigger molecule like hydrogen peroxide, the empirical formula shows only the ratio of atoms. In this case: HO: However, this empirical chemical formula only shows the basic foundation of the molecule. In reality, two HO: molecules come together to form a hydrogen peroxide molecule.
Read Full Article on Empirical Formula- Empirical Formula
2. Molecular Formula
- The molecular formula comes in to show the actual number of atoms within each molecule. Thus, for hydrogen peroxide, the molecular formula is thus: H2O2
- As you can see, this somewhat confuses the actual structure of hydrogen peroxide. While the empirical chemical formula gives clues that the molecule has two oxygen atoms bonded together in the middle, the molecular formula does not clarify. However, the molecular formula is often used to describe molecules simply because it is convenient, and most molecules can be looked up after their formula is identified.
Read full article on Molecular Formula: Molecular Formula
3. Structural Formula
- The structural formula of a molecule is a chemical formula with a more artistic twist. In these chemical formulas, the actual bonds between molecules are shown. This helps the reader understand how the different atoms are connected and thus how the molecule functions in space. There are many different structural, chemical formulas to consider.
- The simplest, the electron dot method, uses colons and periods to show bonds between atoms. Each colon represents a pair of electrons shared between the atoms on either side of the colon. This formula more accurately represents the actual arrangement of atoms within a molecule. In water, the electron dot formula would look like this: H:O: H.
- Another chemical formula, the bond-line formula, also shows the bonds between atoms. Instead of showing each electron that is shared, a line is used to designate an electron pair shared between the atoms. Water, in the bond-line formula, looks like this: H-O-H.
- Scientists have come up with much more advanced formulas and representations of molecules, including three-dimensional ball-and-stick models, space-filling models, and even models which consider the electron density of the atoms being modeled. And these advanced models consider the atoms present and their number and the angles, sizes, and distances between atoms within a molecule. The ball and stick model of water below shows the molecule’s polarity, as the large oxygen atom tends to attract the most electrons.
Importance of Chemical Formula
- Chemical formulae provide insight into the chemical composition of a compound.
- They also represent the ratios in which the constituent elements combine to form the compound.
- The chemical formula of a compound is crucial while representing it in a chemical equation.
- Chemical formulae can also be employed to represent ions, free radicals, and other chemical species.
How to write Chemical Formula ?
In order to write a chemical formula, it is important to know the symbol of the elements present in the compound, the formula of the radicals, and the valency of the elements in that compound.
The following points should be kept in mind while writing a chemical formula:
- Most of the compounds are binary compounds, i.e., they have two elements. Compounds with more than two elements are also known as an atom with a positive charge is called a cation, whereas an atom with a negative charge is called an anion.
- For a compound containing a metal and a non-metal, the metal is named first, followed by the non-metal. For example, NaCl which consists of Na+ (metal ion) and Cl– (non-metal ion).
- Anions are having a -1 negative charge usually have a suffix aside. For example, F– – Fluoride.
- Anions having oxyanions (oxygen + another element) usually have a suffix as –ate. For example – SO42 (Sulphate).
- When a polyatomic anion has H– ion, bi–, or hydrogen is used as a suffix. For example – HCO3–-Bicarbonate or hydrogen carbonate.
Examples of Chemical Formula
Question: Write the chemical formulae for
- Sodium Chloride
- Chemical formula of Hexane = C6H14
It has 6 atoms of carbon and 14 atoms of Hydrogen and is collectively called Hexane.
2. Chemical formula of Sodium Chloride = NaCl
It is also known as Sodium Chloride or common salt. This formula has a single atom of Sodium and a single atom of Chloride.
Always remember that in places where there is no subscript, like in the example above, the
value of atom is presumed to be 1.