Daltons Atomic Theory and its Modifications

Biola Emmanuel - Thu, 18th April, 2019 @ 11:26: AM

Topics in Chemistry

Salts and Types of Salt in Chemistry Separation Techniques Separation Techniques part 2 Separation Techniques part 3 Physical Change, Chemical Change, Element, Compound and Mixture Electrolysis, Electrolyte, Electrode, Anode and Cathode Grahams law of diffusion Physical Properties of Metals Daltons Atomic Theory and its Modifications Periodic table and Classification of Elements

Academic Questions in Chemistry

Please check out our Test Your Knowledge page to see all Questions and Answers

The reaction involving an acid and a base is termed _____.

  • A. Hydrolysis
  • B. Neutralization
  • C. Combustion
  • D. Displacement
  • E. Decomposition
  • F. Sublimation

Which of the following is NOT a type of salt?

  • A. Acid salt
  • B. Basic salt
  • C. Double salt
  • D. Tripple salt
  • E. Complex salt
  • F. Normal Salt

The only metal that exist as liquid at room temperature is _____.

  1. Nickel
  2. Duralumin
  3. Mercury
  4. Lead
  5. Titanium
  6. Cesium

Dalton’s atomic theory:

John Dalton, an English Chemist is considered the father of modern chemistry because of the understanding he brought into the composition of matter and the basis for their chemical reactions. (Remember that chemistry is the study of matter and the changes they undergo). Some of the atomic theory which he postulated in 1808 had to be modified. In this article, we will look into these atomic theories and their modifications.


Atomic Theory 1

  • All matter consists of tiny indivisible particles called atoms.

Modification of Atomic theory 1

Based on the discovery made by Rutherford, atoms can no longer be regarded as indivisible because they can be further divided into the followings:

  • Protons: positively charged particles in the nucleus of an atom.

  • Neutrons: These particles have no charge (neutral) and are found in the nucleus of an atom.

  • Electrons: Negatively charged and revolve round the shell of atoms.

  • Quarks: A quark is a fast moving energy and is comprised of both the protons and neutrons in the nucleus of an atom.


Atomic theory 2

  • Atoms of the same element are identical to each other in every aspect because they have the same shape and mass, while atoms of different elements are different in all respect.

Modification of Atomic theory 2

The discovery of isotopes has shown that not all atoms of the same elements are similar in every aspect. Isotopy is a phenomenon whereby atoms of the same element have the same atomic number but different mass number. As a result, the same element can have a different mass and density. Some of these include:

3517Cl and 3717Cl : Isotopes of Chlorine with mass numbers 35 and 37 respectively.

11H and 21H and 31H : Hydrogen-1, Hydrogen-2 (Deuterium) and Hydrogen-3 (Tritium) are isotopes of hydrogen with masses of 1, 2 and 3 respectively.

Also, the discoveries of isobars have shown that the atoms of different elements are not completely different. Isobar is a phenomenon whereby atoms have the different atomic number but the same mass number. For instance;

147N and 146C are isobars: These are different elements (Nitrogen and Carbon) with the same mass number. Both elements will have the same weight under a specific gravitational force. Read our article on gravity HERE

2411Na and 2412Mg are isobars: These are different elements (Sodium and Magnesium) with the same mass number.


Atomic theory 3

  • Atoms are indestructible and can neither be created nor destroyed.

Modification of Atomic theory 3

With regards to ordinary chemical reaction, this statement remains valid. Since the discovery of radioactivity, radioactive elements have shown that atoms can be created (through a process called nuclear fusion) and destroyed (through a process called nuclear fission). Example of radioactive elements are Thorium-232 and Uranium-238


Atomic theory 4

  • Atoms of different elements can combine with each other in simple whole number ratios to form compounds.

Modification of Atomic theory 4

This statement is true for simple inorganic chemical reaction. With regards to complex organic compounds or molecules, the statement becomes false because they don’t combine in simple whole numbers but rather, they do so in complex numbers. For instance, glucose molecule has a chemical formula of C12H22O11. Starch is another organic compound that contains many repeating units of simple sugars and with a chemical formula of (C6H10O5)n, where "n" is a large whole number


Atomic theory 5

  • Atoms of same element can combine in more than one ratio to form two or more compounds.

Modification of Atomic theory 5

This theory cannot explain allotropy. Allotropy is phenomenon whereby atoms of the same element can exist in different forms in the same physical state. For example, carbon in a solid state can exist in four different forms. These are:

  • Diamond
  • Graphite
  • Graphene
  • Fullerene


Advantages of Dalton’s Atomic Theory

1. His theory gave a clearer explanation of the laws of chemical combination which includes:

  • Law of constant composition
  • Law of multiple proportions

2. Dalton created the distinctions between atoms, molecules and compounds.

3. His work paved way for the discovery of atomic bomb.

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The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals. Please read some interesting facts about gold here