What is a Chemical ? We encounter chemical substances and compounds every day.The substances under the kitchen sink that we use to clean our houses as well as those that are staples in our medicine cabinet are made up of chemical substances. These chemicals are made up of a fixed proportion of , and these atoms are arranged in a certain way. In order to figure out what these proportions are and how they are arranged for any given substance, we need to know the of the substance or compound. A compound is a substance made up of a definite proportion of two or more elements. A chemical formula tells us the number of atoms of each element in a compound. It contains the symbols of the atoms of the elements present in the compound as well as how many there are for each element in the form of subscripts.

Each has a specific , so these chemical substances have their own chemical formula. Let's take a look at the chemical formula of : there are 12 (C) atoms, 22 (H) atoms and 11 (O) atoms. If we look at , we see it has 4 carbon (C) atoms and 10 hydrogen (H) atoms.

Empirical Formula The word empirical is defined as something that is verified by observation. In , we verify facts by performing experiments. So, the is defined as the simplest ratio of whole numbers of elements that make up a compound, and this type of formula is derived from experimental data. Just like how we simplify fractions in math class, in chemistry we can simplify as well. In this case, let's look at the molecular formula of :

While the molecular formula gives us the actual number of atoms of each element in a , the empirical formula gives us the simplest ratio and not the actual number of atoms of an element. Here are some examples of empirical formulas derived from molecular formulas:

Sometimes, there are molecular formulas that are already at their simplest ratio which means they cannot be further reduced. In these cases, the molecular formula is the same as the empirical formula which can be seen with these examples.

In Sucrose, the subscripts 12, 22 and 11 do not have a greatest common factor, so they cannot be further reduced. The same goes with .

STRUCTURAL FORMULA When we simply write the molecular formula, we do not know how the atoms are arranged or which atoms are bonded to each other. The shows both the actual number of atoms of elements in a compound, how the atoms are arranged and which atoms are bonded to one another. Here are the structural formulas of , and ethanol. The molecular formulas of each are reflected below the structural formulas.

Let's look at ethane. It shows that the carbon (C) on the left is bonded to three hydrogen (H) atoms and the other carbon atom. The carbon on the right is also bonded to three hydrogen atoms and the carbon on the left.