Elements and compounds are scientifically pure substances. It means that they cannot be broken down into their constituents by physical processes. In fact, in the case of elements, they cannot be broken down into any more substances since they are made up of the same kind of substances which are the most basic form of matter constituting that particular element. Compounds, on the other hand, are made up of two or more elements chemically bonded together.
At the other end of the spectrum are the mixtures, which are not pure substances and can be separated into their constituents by physical processes. Their constituents are not chemically bonded to each other.
History of Elements
Ancient Greeks had theorised that all matter was essentially made up of five elements-fire, air, water, ether and earth. The ancient Indians had a similar theory. However, later Greeks and Indians acknowledged the existence of atoms as the smallest form of matter.
Some elements like gold, silver and iron have been known to humans for thousands of years. However, the first scientific discovery of an element was made by discovering phosphorus by Henning Brand.
Over the years, several attempts were made to organise the list of known elements. This led to the invention of periodic tales. A Russian chemist, Dmitri Mendeleev is often referred to as the “father of the periodic table”. At present, around 118 elements have been discovered. Each element has a unique atomic number in the periodic table.
History of Compounds
The history of Compounds is no less interesting. However, in the late eighteenth century, it was difficult for scientists to distinguish compounds as separate entities from mixtures. According to Dalton, the chemical composition of compounds remained fixed. However, the scientists had a hard time proving this.
Two sets of arguments were placed in this case. A French chemist, Claude Louis Bethollet was against the idea that compounds had a fixed composition and were different from mixtures. He used the example of metal oxides as his argument. According to him, when a metal is heated at different temperatures, the composition of the oxide changes. He was refuted by his fellow countryman Joseph Proust. According to Proust, metals form different oxides at different temperatures which are not the same compound. Hence the composition of a particular compound remains constant. He also argued that the scientific discovery was not advanced back then to precisely determine the chemical composition of substances and that nominal changes in composition could be attributed to human imprecision. His arguments finally took over and today, there is no scientist who denies that compounds are in fact, different from mixtures. However, even Proust had difficulties explaining the case of Alloys. Today we know that alloys are actually mixtures since they display the properties of their individual constituents.
Types of Elements
Elements can be roughly classified into metals, nonmetals and metalloids.
The metals can be found on the left side of the periodic table. Metals have a few special characteristics or properties which distinguishes them from non-metals. These characteristics are as follows:
- Thermal and heat conductivity
Some examples of metal are iron, copper etc.
Non-metals, in contrast, are found on the right side of the periodic table. These do not display the special characteristics of metals and are known as poor conductors. Some examples of non-metal are oxygen, carbon etc.
Metalloids form the borderline between metals and nonmetals. They show some characteristics of metals and some of the non-metals. Some examples are silicon and arsenic.
Types of Compounds
Compounds are actually a group of two or more elements chemically bonded together. Although the components of a compound cannot be separated by physical processes, it is possible to do so by using chemical reactions. The various types of compounds are listed below:
- Molecular Compounds (chemically held by covalent bonds
- Intermetallic Compounds(chemically held by ionic bonds)
- Ionic Compounds(chemically held by metallic bonds)
- Coordinate covalent bonds holding complexes
Comparison and Differences
- Elements: Composed of the same kind of particles(atoms).
- Compounds: Composed of two or more elements chemically bonded together in a fixed proportion by mass.
Ability to Break Down
- Elements: Elements cannot be broken down into any more basic constituents by any physical or chemical processes.
- Compounds: Compounds can be broken down into their constituents by chemical processes.
- Elements: They are represented by their unique symbols from the periodic table.
- Compounds: They are represented using chemical formulae derived from their constituents.
- Elements: Classified as metals, nonmetals and metalloids based on properties.
- Compounds: Classified based on the chemical bonds holding the constituents together in a compound.
- Elements: Oxygen, Iron, Gold, Aluminium etc.
- Compounds: Water, Aqua Regia, Sodium Hydroxide etc.
Substances found in nature have been classified as pure substances and mixtures. Pure substances include elements and compounds and cannot be broken down into their constituents by physical processes. Mixtures can be broken down into their components by physical processes. Elements are made up of the same kind of particles, while compounds are made up of two or more elements chemically bonded together in a fixed proportion by mass.