Chemical Formulas PDF

The Periodic Table of Elements classifies all elements known to humankind. If there are only 118 elements, how can there be so many more different types of substances in the world? The answer to that question is that elements combine with each other to form molecules, and in many cases, new substanc...

The Periodic Table of Elements classifies all elements known to humankind. If there are only 118 elements, how can there be so many more different types of substances in the world? The answer to that question is that elements combine with each other to form molecules, and in many cases, new substances. Sometimes, atoms of the same element combine to form molecules. Oxygen is a good example of an element molecule because when two atoms of oxygen combine, they still retain the properties of oxygen. In contrast, a compound molecule forms when atoms of different elements combine to make a new molecule. Water is a good example of a compound molecule because it contains different atoms (hydrogen and oxygen). A compound molecule has properties that are distinct from the individual elements. Chemical bonds are the glue that holds elements together. A chemical compound is a substance composed of the same molecules throughout but from more than one kind of atom. Water is considered a chemical compound because all the molecules in water are made up of hydrogen and oxygen atoms. The hydrogen and oxygen are bonded together in a specific ratio (two hydrogens to one oxygen). Chemists use chemical formulas to show this ratio as H2O. A chemical formula tells which elements and how many atoms of each element there are in a chemical compound. The chemical formula is written using the elements’ symbols and sometimes subscript numbers. If there is more than one atom of an element in a compound, a subscript number will appear to the right of the element symbol. The subscript number tells the number of atoms of that element in the compound. If there is no subscript next to an element’s symbol, there is only one atom of that element. Let’s look at the chemical compound calcium carbonate (chalk). The chemical formula is written as CaCO3. This formula tells us there are three different elements in this compound: calcium, carbon, and oxygen. Because there is no subscript number to the right of calcium or carbon, there is only one atom of each in this compound. Oxygen has a subscript 3 after it, which means there are 3 atoms of oxygen in this compound. Interpreting this formula tells us that calcium carbonate is made of one atom of calcium, one atom of carbon, and three atoms of oxygen. As you can see, a chemical formula is a bit like an abbreviation! Chemical Name Magnesium Sulphate Common Name Epsom Formula MgSO₄ Sodium Bicarbonate Baking powder NaHCO₃ Nitrous Oxide Laughing Gas N₂O Here are a few more chemical compounds. See if you can identify the atoms and tell how many of each atom make up the molecules in the compound! Background image by Simone Cimò, CC BY-SA 4.0 via Wikimedia Commons © Kesler Science, 2021