Which postulates of Dalton that is not accepted?

Answer 1

one of the postulates that is not considered true today is that atoms are indivisible^-^

He said that all atoms of a given element are alike. This is not true due to the existence of isotopes. Isotopes are atoms of the same element that have different masses because they have different numbers of neutrons.

During a chemical reaction, atoms can change their identities

Answer 2

To answer this question, we must look at the original postulates of Dalton's Atomic Theory:

1. All Matter Consists of Tiny Particles

Which basically states that matter is made of atoms, a theory that was actually suggested about 2000 years ago by Democritus, a Greek philosopher.

Atoms still stand today as the fundamental unit of matter, made up of numerous subatomic particles that make up the overall characteristic of the atom. Though there are smaller particles making up the atoms and other massless particles have been observed that do not conform to the definition of atoms, for general chemistry understanding of reactions, the observation of matter making up of atoms is correct.

2. All Atoms are indestructible and unchangeable

Which states atoms are immutable and are unchanged in their interaction with other atoms.

This is often the simplification for many general chemistry introductions, that chemical reactions do not change the atoms themselves only their interaction and bonding with other atoms. This was fine and dandy for 19th century chemistry, but there are many other interactions that affect the atoms themselves that were revealed in the 20th century with the advent of quantum theory and instrumentation that could delve beneath the electron shell of the atom. The most dramatic example of these non-atom conserving interactions is the nuclear reactions that so many of us are familiar with, the generation of enormous amounts of energy from mass. Through quantum interactions one type of atoms could be converted into another, as one type of subatomic particle is converted to another, usually less massive, particle. Which leads to the next of Dalton's postulate:

3. Elements are characterized by the mass of their atoms

Which means atoms of the same element have the same Atomic Mass, which is completely unfounded. Elements, as we known now, have numerous different isotopes, or variations on the atomic mass but having the same atomic number thus having the same characteristics as other isotopes of the element. The most common example of which is the comparison between the normal stable Nitrogen-14 and the popularly radioactive Carbon-14, both having atomic masses of 14, but are different elements (N-14 has 7 protons and 7 neutrons, and C-14 has 6 protons and 8 neutrons). Under Dalton's definition of elements, they would be the same element.

The last two are fundamental to general chemistry and still hold today, and are the basis for stoichiometry.

4. When elements react they combine in simple, whole number fractions

Which means elements will always combine in whole number parts or a ratio that reduces to simple fractions, you will never see 1.23 Part hydrogen combining with 3.14 part oxygen. Which essentially reiterates the indivisible nature of atoms in chemical reactions, which means you can't have half an atom attached to a molecule.

5. When elements react they usually combine in more than one simple whole number ratios

Which states that two elements will combine not only in one ratio, but many ratios. This observation reinforces the existence of many compounds that make up the same elements but make up to be different compounds. For instance hydrocarbons are the most ubiquitous example of this postulate, the varying combination of hydrogen and carbon results in numerous different compounds (eg. methane, butane, propane, hexane, cyclo-hexane, just to name a few out of millions)

6. And finally a postulate that Dalton stated that nearly resulted in the general rejection of his entire theory (which you can see did contain a lot of truths) was the assertion that elements only reacted in binary combinations, which means only two elements can react to create compounds, which is just completely false, as empirical evidence during his lifetime showed.

Overall, Dalton's Atomic Theory was the first proposed since the classical ages, and it did spawn the thoughts and theories that would eventually become the modern atomic theory. But analyzing the technology Dalton had to derive the Atomic theory (which consisted of conducting a series of combustion reactions and weighing the results), his mistakes are more than excusable. As the technology progressed and human could delve deeper and deeper into the atom, more and more is discovered about the nature of the subatomic world, which challenges even now the "Modern" Theory of Atoms.

Answer 3

That atoms are indivisible and that all atoms of a given element are identical are not acceptable today.

Answer 4

These postulates are:
· All atoms of a given element are identical. · A given compound always has the same relative numbers of types of atoms.

Answer 5

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