John Dalton formulated an atomic model in 1808 that was able to make sense of some very important concepts within Chemistry, such as the concept of molecules, elements and substances. His model, which was proposed based on discussions made in Ancient Greece by Democritus and Leucippus, determined that the atom had the following characteristics: it was spherical, massive, indivisible and indestructible.
Dalton associated the model of the atom to a billiard ball due to its similarity (massive and spherical) to his proposal. The following is the representation of the atom according to the Dalton model:
Sphere that resembles a billiard ball — representation of Dalton’s atomic model
O dalton model It is very useful to understand some important concepts, such as:
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Chemical element: group of atoms that have the same characteristics. In the following image, we have the representation of two chemical elements, since we have two different atoms.
Representation of two different chemical elements using the Dalton model
Dalton model used to represent a molecule
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Substance: group of molecules. In the following image, we have the representation of a substance, since we have a group of identical molecules.
Group of identical molecules, according to the Dalton model, that form a substance
Analyzing the following representation that uses the dalton model, we can easily perceive the amount of atoms, elements, molecules and substances present:
In the image, there are seven atoms, three chemical elements, three molecules and three substances.
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atoms: 7 (all spheres);
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elements: 3 (red, green, pink);
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molecules: 3 (red, green and pink group);
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substances: 3 (red, green and pink group).
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Mind Map: Dalton’s Atomic Model
* To download the mind map in PDF, click here!
Dalton’s model is still sufficient for us to understand the concept of simple substance. A substance is said to be simple when its molecules are formed exclusively by atoms of the same chemical element. Below is a representation of three simple substances:
Representation of three simple substances using the Dalton model
When analyzing the image, we noticed that a molecule is formed only by blue atoms; the other, only by reds; and the last, only by yellow atoms; which denotes that the three are representations of simple substances since they are formed by equal atoms (same element).
If we have in Dalton’s model a molecule that has different atoms, we will have the representation of what we call composite substancewhich is nothing more than the substance formed by more than one type of atom, that is, more than one type of chemical element.
Representation of a compound substance according to the Dalton model
Finally, we have five molecules in the image below. When observing them, we will realize that they are all different from each other (different combinations of atoms), containing atoms of different elements. Therefore, in this image we will have five compound substances represented.
Representation of five different compound substances according to the Dalton model
* Mind map by Victor Ricardo Ferreira
Chemistry teacher
By Me. Diogo Lopes Dias