Dalton’s atomic theory concerns the atoms and their properties given by the British chemist John Dalton in 1808. This theory was the first attempt to describe all the matters about the atoms. This theory depends on the law of conservation of mass as well as the law of constant composition. According to this scientific theory, all matter is formed by small and indivisible particles known as ‘atoms’. The various elements contain atoms having varying sizes and masses. An individual element’s atom contains the same size and mass.
Dalton’s atomic theory
The general principle of this theory was proposed in 1804 by John Dalton after conducting various experiments and observations, as well as the work of his peers:
Part 1: All matter contains the atoms.
Dalton used the law of conservation of mass and the law of definite proportions to explain the idea of atoms. He suggested that all matter contains tiny and indivisible particles called atoms. These are “solid, massy, hard, impenetrable, and movable particle(s)”.
Part 2: All atoms of a certain element contain in same masses and properties.
Dalton described that every single atom of an element, such as silver, is the same as every other atom of that element. He also described that the atoms of one element are completely different from the atoms of all other elements. For example, a neon atom is different from a silicon atom. They may have similar boiling points, melting points, density, and electronegativities, but most of the properties of elements must be different from each other.
Part 3: Atoms from different elements contain different properties and vary in mass and size.
Two or different types of atoms are combined to form compounds. An example, aluminum chloride is formed by the combination of aluminum with chlorine at a definite ratio. Aluminum is a metal and chlorine is a toxic gas which are mixed to form aluminum chloride salt. The crystal of aluminum chloride is essential to conduct various chemical reactions.
Part 4: Atoms take part in chemical reactions to form compounds.
John Dalton proposed that there is no chemical reaction to destroy or create atoms. They are just rearranged in a specific way to form the compound. When the Magnesium atom and chlorine atom react to each other, then we get the Magnesium chloride compound.
The summarized form of the postulates of John Dalton’s atomic theory is given below:
All matter contains tiny and indivisible particles called atoms.
The atoms of a specific element are identical in mass, size, and other properties. However, atoms from different elements have different properties and vary in mass and size.
Atoms cannot be created or destroyed in a chemical reaction. Furthermore, atoms cannot be subdivided into smaller fragments.
Atoms from different types of elements can attach in fixed whole-number ratios to form various chemical compounds. Atoms can be combined, separated, or rearranged through various chemical reactions.
Limitations of Dalton’s Atomic Theory
There was no necessary instrument to see or otherwise experiment on individual atoms by John Dalton. So there were some limitations which are given below:
This theory states that all matter contains tiny and indivisible particles called atoms. But it is not a correct statement nowadays because the discovery of protons, electrons, and neutrons disproved this matter.
This theory states that the atoms of a specific element are identical in mass, size, and other properties. It is not a correct statement nowadays because the discoveries of isotopes of elements have different atomic masses
This theory states that atoms from different elements have different properties and vary in mass and size. But it is not correct nowadays because discoveries of isobars of elements have the same atomic mass numbers.
This theory states that atoms from different types of elements can attach in fixed whole-number ratios to form various chemical compounds. However, it is not correct nowadays because various complex organic compounds do not maintain simple ratios of constituent atoms to make compounds. Example: Sucrose.
There exist various chemical allotropes like diamond and graphite whose properties can never be explained by this theory.
Advantages of Dalton’s Atomic Theory
This theory follows the law of conservation of mass and the law of constant proportions.
This theory is helpful in differentiating between elements and compounds.
The law of conservation of mass
This law states that matter cannot be created or destroyed in a closed system area. It means that the amount of each element is unchanged during the starting materials and the products in chemical reactions. This law is very helpful for balancing chemical equations properly.
The law of constant composition
This law states that there is the same proportion of the same elements in a pure chemical compound. For example, the molecular formula of table salt is NaCl which contains the elements sodium and chlorine. The proportion of sodium and chlorine is the same during the formation of NaCl at a pure state.
Frequently Asked Questions (FAQs)
What is Dalton’s atomic theory?
This theory is the first attempt to reveal the atoms and their properties given by the British chemist John Dalton in 1808.
What are the main postulates of Dalton’s atomic theory?
Atoms in elements are completely tiny and indivisible particles.
It has unique mass, size, and other properties for the same atoms.
It has different mass, size, and other properties for the different atoms.
There is no possibility of dividing the atoms into smaller fragments.
The various chemical compounds are formed by reacting with the atoms in a certain ratio.
What are the limitations of Dalton’s atomic theory?
The atoms can be divided in a specific way and electrons, protons, and neutrons are found. So this theory is unable to explain that atoms are tiny and indivisible.
This theory cannot explain the matter of isotope.
This theory is unable to express the matter of isobars.
This theory does not state the matter of allotropic issues.
What are atoms constituted of?
Atoms are formed by the proper management of negatively charged electrons, positively charged protons, and neutral neutrons.
Who is John Dalton?
John Dalton was a British chemist who gave a good atomic model in 1804 after conducting some research.
