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Dalton's Atomic Theory - Definitions, Practice problems & FAQs

Dalton's Atomic Theory - Definitions, Practice problems & FAQs

Around 340 BC Democritus was the first person who tried to define the atom but after around 2200 years dalton was the first person who publish the first atomic theory. Can you guess which fundamental theory about the composition of matter dominated science for the 2200 years before Dalton’s atomic theory?

Aristotle around 300 BC, Aristotle (A philosopher not a scientist) have a problem with Democritus' atomic theory. According to Aristotle, all matter was made up of the four elements: fire, earth water, and air. He was a famous personality of that era and this theory dominated science for many years. In the year 1808, Dalton was the first person who introduced the atomic theory -All matter is made up of atoms, the smallest particle (indivisible). 

By 1800, chemistry had undergone one of the most dramatic intellectual revolutions in millennia, when scientific rigor was given to the ancient science of alchemy, resulting in the 18th century's Chemical Revolution.

And to think, that Dalton contributed only towards the development of atomic theory would be incorrect. During this period, he also published Meteorological Observations and Essays. Dalton suggested several theories during his early research years, including the hypothesis that the atmosphere is made up of a mixture of gases. He also looked at colour blindness and atomic masses. The study of the atomic mass led to the development of various scientific rules and ideas.


Table of contents

  • Dalton’s atomic theory
  • Dalton’s atomic symbol
  • Story of atomic symbols
  • Limitations of Dalton's atomic theory
  • Practice problems
  • Frequently asked questions-FAQs

Dalton's atomic theory

In 1808, John Dalton published an atomic theory in his book “A new system of chemical philosophy” and the main axioms of Dalton’s atomic theory are:

  • All matter is made up of small indivisible entities called atoms.
  • All atoms of a particular element are identical in mass, size, and the rest of all other properties. However, atoms of different elements have different properties and vary in their mass and size.
  • Atoms can neither be created nor destroyed. (atoms cannot be divided into simpler particles).
  • Atoms of different elements can combine with each other in whole-number ratios in order to form compounds.
  • Atoms participate in chemical reactions. Atoms can be rearranged, combined, or separated during a chemical reaction.

Dalton’s atomic symbol

Dalton developed pictorial symbols of a few elements (almost 20) and with the help of this symbol, he represented the structure of some simple molecules.


Story of atomic symbols



Advantages of Dalton's atomic theory

  • Dalton's atomic theory is notable for not violating a number of key rules of chemical combination, including the law of definite proportions, the law of multiple proportions, and the law of conservation of mass.
  • Dalton's atomic theory also allowed scientists to discriminate between elements and compounds, which was a considerable gain.

Limitations of Dalton's atomic theory

The following are some significant flaws in Dalton's atomic theory:

  • It doesn't take into consideration subatomic particles: Dalton's atomic theory asserted that atoms were indivisible. The discovery of subatomic particles such as protons, electrons, and neutrons, on the other hand, invalidated this hypothesis.
  • Isotopes aren't taken into account: According to Dalton's atomic theory, each element's atoms have the same mass and density. Different isotopes of elements, on the other hand, have different atomic masses (For example hydrogen, deuterium, and tritium).
  • Isobars aren't taken into account: According to this idea, the masses of atoms in two different elements must differ. However, it is conceivable for two different elements to have the same mass number. Isobars are atoms that fall under this category (Example: Ar40 and Ca40).
  • Compounds do not have to be formed in straightforward whole-number ratios: Certain complicated organic compounds don't have simple atom-to-atom ratios. Sugar/sucrose is a good example (C11H22O11).
  • Allotropes are not taken into account by the theory: Dalton's atomic theory cannot explain the variations in the properties of diamond and graphite, which both contain solely carbon.

Practice problems

Q 1. Dalton's atomic theory does not include which of the following postulates?

a. Single types of atoms have the same size and shape but have different atomic masses
b. Atoms are neither created nor destroyed in a chemical reaction
c. The masses of various elements vary.
d. None of these

Answer: (A)
According to Dalton’s atomic theory, all atoms of a particular element are identical in mass, size, and rest all other properties. However, atoms of different elements have different properties and vary in their mass and size.

Q 2. According to Dalton’s atomic theory, each and every matter is made up of indivisible

a. Electrons
b. Atoms
c. Ions
d. All of these

Answer: (B)
According to Dalton’s atomic theory, All matter is made up of small indivisible entities called atoms and all atoms of a particular element are identical in mass, size, and rest all other properties. However, atoms of different elements have different properties and vary in their mass and size.

Q 3. What is the name of the book in which Dalton published his famous atomic theory for the first time

a. A new system of atomic philosophy
b. Mathematical principle of natural philosophy
c. A new system of chemical philosophy
d. None of these

Answer: (C)
In 1808, John Dalton published an atomic theory in his book “A new system of chemical philosophy”. The mathematical principle of natural philosophy is written by Newton.

Q 4. Which is the first published atomic theory

a. Quantum mechanical model
b. Bohr’s atomic model
c. Rutherford atomic model
d. Dalton’s atomic model

Answer: (D)
In the year 1808, Dalton was the first person who introduced the atomic theory -All matter is made up of atoms, the smallest particle (indivisible).

Frequently asked questions-FAQs

Q 1. Dalton failed to explain which experimental theory?
Answer: Dalton failed to explain the Gay lussac law of combining gaseous volume. According to gay lussac, when the volume of gases involved in a chemical reaction is measured at the same temperature and pressure, they display simple whole-number ratios to one another. At that time Dalton was unable to explain the free existence of atoms, which means he was not able to understand why some type of atom will combine and form molecules like H2, O2 etc.

Q 2. Who first proved that atoms are composed of subatomic particles?
Answer:
J.J Thomson was the first person who proved that atoms are composed of negatively charged particles (first named corpuscles and further named electrons) which have a very very low charge to the mass ratio in comparison to H+ ion, during the study of conduction of electricity by gases.

Q 3. Which first theory given by Dalton, made him popular in the scientific community?
Answer: Atomic theory was published in 1808 but the first major achievement of Dalton was Dalton’s law of partial pressure. This experimental law was observed in 1801 and published in 1803. Further some major contributions like atomic symbol, relative atomic weight, the law of multiple proportions, Dalton’s atomic theory, contribution to Henry’s law, etc.

Related Topic

Millikan’s oil drop experiment

Bohr’s atomic model

De Broglie equation

Discovery of electrons

Planck's Quantum Hypothesis

Thomson's atomic model

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