What is the difference between element, compound and mixture?

Today we are going to see three very basic concepts: element, compound and mixture. Sure they seem obvious to those with an elementary scientific training, but their meaning is also surely not entirely clear to many others.

Definition

Any substance, understood as type of mattercan be classified according to many and varied criteria, including the macroscopic homogeneity or the type of atoms and molecules that compose it. Based on these characteristics, a substance could be a pure substance, which in turn can be an element or a compound, or a mixture (non-pure substance).

Element

One item is the simplest form of a pure substance. It is always made up of same kind of atomsand therefore an element cannot be separated or broken down into other substances.

An element cannot be formed by the combination of other substances either, only by the combination of that type of atoms (at least not by ordinary physical and chemical methods, although it could be done by nuclear fission and fusion techniques, for example by beta decay).

A pure elementary substance can also be made up of molecules but they will be molecules made up of only one type of atoms or type of element. For example, oxygen is an element, a type of atom, but in atmospheric air the most abundant oxygen is molecular oxygen, which is made up of two bonded oxygen atoms (Otwo).

In summary, an element has these characteristics:

  • It is made up only one type of atom
  • cannot be separated into simpler types of substances neither by physical methods nor by chemical methods
  • can exist as atoms (for example argon) or as molecules (for example nitrogen), but never as molecules of different atoms.

Compound

A compound is also a form of pure substance, since it is always formed by the same type of moleculesBut they are molecules that contain several types of atoms.

Compounds can be break down into elements and can be formed by combination of elements in a chemical reaction.

However, compounds, as a pure substance, always appear in a homogeneous phase and cannot be separated into its components by physical methods, only by chemical methods.

The compounds, therefore, meet these requirements:

  • its about two or more types of atoms bondedthat is, they are made up of molecules with two or more elements
  • always contain the same types of atoms and in the same proportion. For example, the water molecule is always made up of 2 hydrogen atoms and 1 oxygen (HtwoEITHER).
  • can be broken down into simpler substances (into the constituent elements) by chemical methods but not by physical methods
  • the compound properties are different from the properties of separate elements. For example, the properties of water as a substance have nothing to do with the properties of hydrogen or oxygen.

Mixture

Mixtures can be understood as impure substances, as opposed to elements and compounds, or as a physical mixture of pure substances. Mixtures are made up of several elements and/or compounds mixed together. random proportions which are not always fixed.

Also, unlike compounds and elements, mixtures can be separated into their components by physical methods. For example, if there is a water-soluble and an insoluble substance in a mixture, both could be separated by decantation.

Mixtures can be homogeneous or heterogeneous. If the mixture is homogeneous, the composition in any part of the mixture is the same, while heterogeneous mixtures have a composition that varies from one part to another.

In addition, the mixtures may contain substances in different phases. For example, liquid and solid.

The key characteristics of the blends are:

  • are made up of two or more elements and/or compounds physically mixed
  • its components can be separated by physical methods into pure substances, and these, if they are compounds, can be decomposed in turn into elements.
  • they often retain many properties of their components
Comparative element, compound and mixture
ElementCompoundMixture
Phase111 or more
CompositionUniformconstant proportionsWithout a defined ratio
Separation by chemical methodsNopeYesYes
Separation by physical methodsNopeNopeYes
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