Dalton's Atomic Theory

  Postulates and limitations of Dalton’s atomic theory about atoms and matter  

 

  Dalton’s atomic theory was proposed by English physicist and chemist John Dalton in the year 1808 to describe the structure of atoms. According to Dalton’s atomic theory, an atom is an indivisible and indestructible building block of matter and nothing smaller existed. Dalton given some novel postulates about atoms which are,

• All matter is formed by tiny, indivisible particles are called atoms.
• The atoms of specific elements are identical in mass, size, and other properties but atoms of different elements show different types of mass, size, and other properties.
• Atoms of different elements can neither be created nor destroyed.
• The compounds are formed from different atoms by a fixed whole number.
• Atoms are arranged, combined, or separated by different types of chemical processes.

Limitations of Dalton’s Atomic Theory

At the turn of this century, much valuable information about atoms was given. These clearly indicated that Dalton's atom no longer grated its position.

• Instated of Dalton's theory, an atom is composed of further subatomic particles such as electron, proton, and neutron.
• It does not account for isotopes of periodic table elements because Dalton's atomic theory states that the atoms of specific elements are identical in masses. For example, isotopes of hydrogen-like protium, deuterium, and tritium have mass numbers 1, 2, and 3 respectively.

Today an atom is considered to be made up of a tiny nucleus carrying neutrons and protons. This tiny nucleus has around itself certain negatively charged particles of negligible mass or electrons arranged in a definite order.

Today an electron is considered to have standing waves. The probability of discovering a particular electron in a certain region of space around the nucleus is called orbitals. Present-day electrons hold the key to the chemical world. Electronic configuration or arrangement can be used for understanding the chemical elements and their properties.

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