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Describe the main points of Dalton's atomic theory and then explain what points of the theory are still accepted in modern atomic theory and what points have been changed as the result of later experiments and discoveries.

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According to Dalton's Atomic Theory, matter is made up of atoms, which are indivisible and indestructible particles. All the atoms of the same chemical element are equal in mass and properties and different from the atoms of any other element. The compounds are formed by combinations of atoms of different elements. Modern Atomic Theory Indicates that all matter is made up of atoms, and cannot be destroyed or created. Atoms are made of electrons, protons, and neutrons, it is not indivisible but it is the smallest particle that takes part in chemical reactions. The atoms of an element can have variable masses, that is called isotopes. The atoms of different elements can have the same mass number. The bases of the atomic theory were not new, but I contribute to discovering a way to obtain the atomic weight, and also by means of this theory the standard symbols appear for the elements.

Explanation:

The postulates of the Dalton's Atomic Theory are;

  1. Everything is composed of atoms, which are the indivisible building blocks of matter and cannot be destroyed.
  2. Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements. That is, all atoms of an element are identical.
  3. Atoms cannot be created or destroyed.
  4. Atoms of different elements may combine with each other in a fixed, simple, whole number ratios to form compound atoms.
  5. A chemical reaction results in the rearrangement of atoms in the reactant and product compounds.
  6. The atom is the smallest unit of matter that can take part in a chemical reaction.

Points changed;

1. The indivisibility of an atom was proved wrong: advances in the field of science revealed an atom can be further subdivided into protons, neutrons and electrons.

2. According to Dalton, the atoms of same element are similar in all respects. However, atoms of some elements vary in their masses and densities. The discovery of isotopes proved this to be wrong. Isotopes are atoms with different mass number but same atomic number For example, hydrogen has three isotopes with mass numbers 1, 2 and 3.

3. Nuclear chemistry shows that indeed atoms can be destroyed (Nuclear Fission). The destroyed atoms is converted into energy.

4. According to Dalton, atoms of different elements combine in simple whole number ratios to form compounds. However this is not the case in complex organic reactions involving compounds like RNA, Polymers etc.

Point Still Accepted;

1. An atom is indeed the smallest particle that takes part in chemical reactions.

2. A chemical reaction results in the rearrangement of atoms in the reactant and product compounds.

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