Pure substances in chemistry are a classification of matter (substances) that are made up of all the same type of atom (elements), or all the same, molecules (covalent bonds), or all the same ionically bonded elements (compounds).
Get free estimates from chemistry tutors near you.In chemistry, pure substances are only two things: elements or compounds. Elements are substances made up of only one kind of atom. Currently, the Periodic Table of the Elements recognizes 118118 such pure substances. Compounds are molecules (covalently bonded) or units of ionic compounds.
Whether element, molecule, or compound, pure substances share similar physical and chemical properties. These predictable properties make pure substances the foundation of chemistry because known interactions can be used to form new materials and new types of matter.
All pure substances will also show the same chemical properties regardless of where they are found. Chemical properties, meaning behavior of the pure substance during chemical changes, include:
All matter is either a pure substance (atoms or compounds) or mixtures. Heterogeneous mixtures are not pure substances because they have variable compositions. Mixtures are formed by combining different substances.
There are two types of mixtures; homogeneous mixtures and heterogeneous mixtures.
Heterogeneous mixtures do not have the same characteristics as pure substances. For example, one sample of a heterogeneous mixture can have different physical and chemical properties than a second sample from the same mixture.
In addition, mixtures are made up of more than one type of atom, compound, or molecule, making them impure.
Examples of mixtures are a bowl of different fruits, a jar full of coins, and sand at the beach.
As said earlier, every one of the 118 elements on the Periodic Table is a pure substance, so you can start your search for examples with hydrogen, atomic number 1, and continue through to oganesson at 118.
Pure substances that form compounds and molecules include, well, everything around you that is not a mixture. For example, the molecule for sugar or sucrose, C 12 H 22 O 11 ___ C 12 H 22 O 11 is a pure substance similar in sweetness to another pure substance, the molecule fructose, C 6 H 12 O 6 ___ C 6 H 12 O 6 . Millions of molecules, all pure substances, exist.
Baking soda (sodium bicarbonate, N a H C O 3 NaHC_ N a H C O 3 ) is a molecule, while lithium hydroxide ( L i O H LiOH L i O H ) is only a compound, not a molecule; hundreds of thousands of such compounds, all pure substances, exist.
Atoms of different elements can bond together using ionic bonds, but these are not considered molecules. Instead, they are still pure substances and are often referred to just as units of the compound.
An example of a chemical compound that is a pure substance but not a molecule is sodium chloride, table salt, which is formed when a sodium atom gives up an electron to a chlorine atom, creating a positive sodium ion and a negative chlorine ion called chloride. This chemical reaction created the pure substance we know as table salt.
Here is the chemical formula for salt:
N a + C l = N a C l Na+Cl=NaCl N a + Cl = N a Cl
The pure substance formed, N a C l NaCl N a Cl , is formed through electrostatic interactions, not the much stronger chemical bonds of covalently bonded atoms that form molecules.
Any substance composed entirely of one type of atom is considered an element and a pure substance. From the lightest element, hydrogen, to the heaviest element, oganesson.
The current iteration of the Periodic Table of the Elements, as approved by the International Union of Pure and Applied Chemistry (IUPAC), shows 118 elements, every one of them a pure substance.
Covalent bonds (two or more atoms sharing electrons) create molecules. A molecule is an arrangement of two or more atoms forming the smallest identifiable unit of a pure substance. If the molecule is broken apart, it has neither the physical nor chemical properties of the pure substance.
Molecules exist in many degrees of complexity. The simple diatomic hydrogen is composed of just two hydrogen atoms forming H 2 _ H 2 . Or O 2 _ O 2 , which is the "dioxide" part of carbon dioxide. And the incredibly complex molecule known as PG5.
