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Atomic Model of Dalton

The atomic model of Dalton was the first attempt to describe all matter in terms of atoms and their properties scientifically. The idea of ​​atoms was invented by two Greek philosophers, Democritus and Leucippus in the fifth century BC. The Greek word ατoμoν (atom) means  indivisible  because he believed that atoms could not be broken into smaller pieces.

Today, we know that atoms are formed by a  positively charged nucleus  in the center surrounded by  negatively charged electrons  . However, in the past, before the structure of the atom was correctly understood, scientists devised many   different models or  images to describe the appearance of atoms.

JOHN DALTON 

Atomic model presented  in  : 1803

Nickname for your model:   Billiard ball model

John Dalton (September 6, 1766 – July 27, 1844) was an English chemist, physicist and naturalist. He is best known for proposing modern atomic theory also called Dalton’s atomic model and for his research on color blindness, which he suffered from and which caused him a visual defect related to color perception.

Although it is two centuries old, Dalton’s theory is still valid in modern chemical thinking.

Dalton took the idea of ​​the divisibility of matter to explain the nature of atoms. He carefully studied the laws of chemical combinations and came to a conclusion about the characteristics of atoms. Which are the following.

Dalton atomic theory

Part 1: All matter is made of atoms.

Dalton hypothesized that the law of conservation of mass and the law of definite proportions could be explained using the idea of ​​atoms. He proposed that all matter is made of small indivisible particles called atoms, which he imagined as “solid, solid, hard, impenetrable and mobile particles.”
It is important to keep in mind that since Dalton did not have the necessary instruments to see or experiment with individual atoms, he had no idea if they could have any internal structure. We could visualize the Dalton atom as a piece in a molecular modeling kit, where the different elements are spheres of different sizes and colors. While this is a practical model for some applications, we now know that atoms are far from solid spheres.

Part 2: All atoms of a given element are identical in mass and properties.

Dalton proposed that each atom of an element, like gold, is the same as any other atom of that element. He also noted that the atoms of an element differ from the atoms of all other elements. Today, we still know that this is mostly true. A sodium atom is different from a carbon atom. The elements may share some boiling points, melting points and similar electronegativities, but no two elements have the same exact set of properties.
Image of a molecular modeling kit that includes multiple types of plastic spheres in different colors representing elements and “joints” of stick-type plastic.
A basic molecular modeling kit, which includes spherical atoms of different size and color that can be connected by sticks to represent chemical bonds. Image credit: «Photo of the modeling kit» by Sonia in Wikimedia Commons, CC-BY 3.0

Part 3: Compounds are combinations of two or more different types of atoms.

In the third part of Dalton’s atomic theory, he proposed that the compounds are combinations of two or more different types of atoms. An example of such a compound is table salt. Table salt is a combination of two separate elements with unique physical and chemical properties. The first, sodium, is a highly reactive metal.
The second, chlorine, is a toxic gas. When they react, the atoms combine in a ratio of 1: 1 to form white crystals of  N, a, C, l , which we can sprinkle on our food.
Since atoms are indivisible, they will always be combined in simple proportions of whole numbers. Therefore, it would not make sense to write a formula like  N, a, initial subscript, 0, point, 5, final subscript, C, l, initial subscript, 0, point, 5, final subscript  Because you can’t have half an atom!

Part 4: A chemical reaction is a rearrangement of atoms.

In the fourth and last part of Dalton’s atomic theory, he suggested that chemical reactions do not destroy or create atoms. They simply rearranged the atoms. Using our salt example again, when sodium is combined with chlorine to produce salt, the sodium and chlorine atoms still exist. They simply rearrange to form a new compound.

What is the atomic model of Dalton?

It is based on the 4 main Dalton postulates (not all are true) about his atomic theory today. Due to the discoveries of sub-atomic particles.

Characteristics and postulates of Dalton’s atomic theory

1) All matter is made of atoms. Atoms are indivisible and indestructible.

2) All atoms of a particular element are similar in all aspects, either in their physical or chemical properties.

3) The compounds are formed by a combination of two or more different types of atoms.

4) A chemical reaction is a rearrangement of atoms.

Description of Dalton’s atomic model

Dalton’s atomic model is based on a series of postulates and two laws to explain the constitution of all things. Taking up the old idea of ​​the atom. Specifically, the one offered by the philosopher of Nature: Democritus.

His particular contribution resulted in substantiating this view in a scientific way. Properly, from modern science. So he adapted it to the knowledge already acquired and empirically tested.

Explanation of Dalton’s atomic model

Dalton’s atomic model has 4 moments in his theory. From the first one begins with two fundamental laws from which the first 3 postulates that we will touch in the following section are deduced. Then, from these the 4th section is deduced, for its second moment . In the third moment the 5th postulate is deducted and, in the fourth moment, its 6th postulate.

Dalton’s atomic model theory

This is nothing more than the result of the postulates that are accepted on it and we have addressed previously. But, also, it is at first its generations. Let’s see how Dalton put into play each of them to give a satisfactory explanation that endures in history until today.

Starting from the hypothesis raised by it of the law of conservation of mass and the law of defined proportions, the first three postulates are obtained . Now, putting them into play, the fourth postulate was obtained. Already here, what he did was propose from the previous postulates the 5th and prove it. And finally, he obtained the 6th postulate.

Dalton atomic model scheme

Dalton atomic model scheme

It consists of two laws: the conservation of mass and the law of fixed stoichiometry proportions. And, six postulates that satisfy each other, these are : The atoms belonging to the same element are equal to each other. Every compound is formed from the combination of at least 2 different atoms.

The chemical reaction is a re-configuration of atoms. All matter is made up of atoms. Its minimal structure. Each atom is indivisible and indestructible. Atoms belonging to different elements are not equal at all. That is, its properties are excluded.

Postulates of Dalton’s atomic model

Postulates of Dalton's atomic model

All matter is made of atoms. This means that all things, from the greatest to the smallest, are made of atoms. Even the elements. Normally, the sets in which reality is separated are usually encompassed as macro and microcosm.

Each atom is indivisible and indestructible. I take this idea directly from the ancient studies of the Greeks. Precisely, Democritus . So, since everything that exists has atoms, it would be foolish to assume that there are no in any condition.

Atoms, as belonging to the same element, are equal in everything. This applies both to its dimensions, that is, width, height and fineness, as well as to its mass, weight, functionality, among other things. From here the following postulate could be extracted: If the atom belongs to an element, it will not be equal to those of another element.

Every compound is formed by the combination of at least 2 or more different types of atoms . This means that something that is different from a kind of aggregate of atoms does not arise from the same atom, no matter how many combinations are attempted.

Finally, a chemical reaction is nothing more than a re-organization of atoms. That is, these are nothing more than the result of union, separation or reorganization of atoms that gives rise to something new. But, it is clear, it is only a re-configuration from the atoms that are had. There are no “new atoms” but what you already have.

Contributions of Dalton’s atomic model

At the time, this model made it possible to clarify for the first time the reason why chemical substances reacted in fixed (or defined) stoichiometric proportions. It also gives an account of why the formation of two or more different compounds from the same substances given. And, in addition, the most revolutionary, explained each substance from its fundamental constituents, atoms.

It is very important to remember that science was being formally born in Europe at the end of the 18th century. Although each of the various contributions of the most diverse scientists was later passed, it is important to emphasize the following . Dalton’s atomic model explained the bulk of the chemistry of the eighteenth and nineteenth centuries, at least at the beginning of it .

Limitations of Dalton’s atomic model

Limitations of Dalton's atomic model

Clearly all our knowledge is limited by the advances that are made. So, Dalton’s model was no less . Thus, it could not obtain a greater depth in the knowledge of the atom as that contributed in the twentieth century. As, for example, the fact that it is not the tiniest, but that they are made up of protons, neutrons and electrons.

Without wanting to be so close to us. Dalton’s model did not have a greater perspective because only a few elements and minimal characteristics of him were known, even poorly. So some of its failures derive from the bad information received.

Dalton Atomic Model Errors

John Dalton thought that atoms always remained individual. So, from his theory, it would be wrong to deduce the possibility that they can be found as molecules. Also, believing that every compound was nothing more than the union between at least two different atoms, he deduced that the water configuration was HO and not H2O.

Finally, his tools were still very primitive compared to the current ones. For what they were deduced, thanks to it, erroneous calculations . As, for example, the fact that the value of oxygen was 5.5.

Images of the atomic model of Dalton

Based on all his observations, Dalton proposed his atom model. It is also known as the billiard ball model. He defined an atom as a spherical structure, since the concepts of atomic nucleus and electrons were unknown at that time. If you asked Dalton to draw the diagram of an atom, he would simply draw a circle!

dalton model
Dalton model image

Later, he tried to symbolize atoms, and became one of the first scientists to assign such symbols. He gave a specific symbol to each atom, here some of his sketches.

dalton model

History of Dalton’s atomic theory

Although the concept of the atom dates back to the ideas of Democritus, the English meteorologist and chemist John Dalton formulated the first modern description of it as the fundamental component of chemical structures. Dalton developed the law of multiple proportions (first presented in 1803) by studying and expanding the works of Antoine Lavoisier and Joseph Proust.

Proust had studied tin oxides and found that their masses were 88.1% tin and 11.9% oxygen or 78.7% tin and 21.3% oxygen (these were tin oxide (II) and tin dioxide, respectively). Dalton observed from these percentages that 100 g of tin will be combined with 13.5 g or 27 g of oxygen; 13.5 and 27 form a ratio of 1: 2. Dalton discovered that an atomic theory of matter could elegantly explain this common pattern in chemistry: in the case of Proust tin oxides, a tin atom will be combined with one or two oxygen atoms

Dalton also believed that atomic theory could explain why water absorbed different gases in different proportions: for example, he found that water absorbed carbon dioxide much better than nitrogen. Dalton hypothesized that this was due to differences in the mass and complexity of the respective gas particles. In fact, carbon dioxide (CO  2  ) molecules are heavier and larger than nitrogen (N 2  ) molecules  .

Dalton proposed that each chemical element is composed of atoms of a unique and unique type, and although they cannot be altered or destroyed by chemical means, they can combine to form more complex structures (chemical compounds). Since Dalton reached his conclusions by experimenting and examining the results empirically, this marked the first truly scientific theory of the atom.

Bases for Dalton’s theory.

Dalton based his theory on two laws: the law of conservation of mass and the law of constant composition.
The  law of conservation of mass  says that matter is not created or destroyed in a closed system. That means that if we have a chemical reaction, the quantity of each element must be the same in the starting materials and in the products. We use the law of conservation of mass every time we balance equations!
Salt atom structure
A chemist thinks of table salt as sodium and chloride ions arranged in a glass lattice structure. Image credit: «Salt image» by OpenStax Anatomy and Physiology, CC-BY-NC-SA 4.0.
The  law of constant composition  says that a pure compound will always have the same proportion of the same elements. For example, table salt, which has the molecular formula.  N, a, C, l , contains the same proportions of the elements sodium and chlorine, regardless of the amount of salt you have or where it comes from. If we combined some metallic sodium and chlorine gas, something that I would not recommend at home, we could make more table salt, which will have the same composition.
Verification of concepts:  a scientist who has been traveling through time since the beginning of the 18th century decides to carry out the following experiment: take a 10 gram sample of ethanol (  C, H, initial subscript, 3, final subscript, C, H, initial subscript, 2, final subscript, O, H ) and burns it in the presence of oxygen in an open vessel. Once the reaction is over, the beaker is empty. Does this result violate the law of conservation of mass?

Scientific defects:

The main defect in Dalton’s theory, that is, the existence of molecules and atoms, was corrected in principle in 1811 by Amedeo Avogadro. Avogadro proposed that equal volumes of any two gases, at the same temperature and pressure, contain equal numbers of molecules. In other words, the mass of the particles of a gas does not affect the volume it occupies.

Avogadro’s law allowed him to deduce the diatomic nature of numerous gases by studying the volumes to which they reacted. Therefore, Avogadro was able to offer more precise estimates of the atomic mass of oxygen and several other elements, and made a clear distinction between molecules and atoms. Unfortunately, these and other discoveries contradicted and refined Dalton’s theories.

For example, since then scientists have discovered that the atom, which was once thought to be the smallest part of matter, can in fact be subdivided into even smaller elementary particles. And while Dalton conceived as atoms as a single entity without separation between positive, negative and neutral charges, subsequent experiments by JJ Thomson, Ernest Rutherford and Neils Bohr revealed a more complex structure for the atom.

These theories were then validated by observations made with the electron microscope. We also know that atomic weight is a product of the structure of the atoms themselves. Therefore, Dalton’s Atomic Model, in its purest form, is now only considered valid for chemical reactions. However, this does not diminish Dalton’s contribution to modern science.

Dalton atomic model summary

  • Dalton’s atomic theory was the first complete attempt to describe all matter in terms of atoms and their properties.
  • Dalton based his theory on the law of conservation of mass and the  law of constant composition  .
  • The first part of his theory states that all matter is made of atoms, which are indivisible.
  • The second part of the theory says that all the atoms of a given element are identical in mass and properties.
  • The third part says that the compounds are combinations of two or more different types of atoms.
  • The fourth part of the theory states that a chemical reaction is a rearrangement of atoms.
  • Parts of the theory had to be modified based on the existence of subatomic particles and isotopes.

Proposed year of the Dalton atomic model

Dalton Atomic Model Year

Dalton’s atomic model was proposed and modified hereinafter, between 1803 and 1807, at 37 years of its creator. By the way, it was considered “billiard ball”, due to the conclusion that the atoms were solid and hard spheres . From there, the various explanations were given with wooden balls which reaffirmed his nickname.

Atomic model of Dalton mockup

Want to know more about the dalton model? Look at this mockup of images of the atomic model of Dalton, where the different atomic models are bought.

dalton mockup

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