Атомна теорія Дальтона

John Dalton, a British chemist, proposed his theory about atoms in the early 1800s. The theory was not initially accepted, but is now considered a foundation for modern chemistry. It should be known, however, that his theories were not all correct.

$1.$ All matter is made of atoms.

$2.$ Atoms cannot be created nor destroyed, and they are indestructible; they cannot be broken into smaller parts. This was based on the Law of Conservation of Mass. It was later learned that atoms can break into smaller parts. Chemical reactions involve a separation, combination, or rearrangement of atoms.

$3.$ All atoms of an element are identical, in both mass and properties. Atoms of different elements have different mass and properties. In modern chemistry, we now know that sometimes, atoms of the same element may have different masses because the number of neutrons can vary. We call these variations isotopes. This is why the atomic mass of an element is actually an average of the masses of its different isotopes. His theory about atoms of different elements has been proven to have exceptions as well.

$4.$ Compounds are formed by multiple kinds of atoms. When atoms of different elements form compounds, they combine in a simple, whole number ratio.

$5.$ Atoms of the same element can form multiple compounds when they combine in more than one ratio.

Having trouble remembering? Maybe this video will help!

In 1804, John Dalton came up with the first full set of rules describing how atoms form all of the different substances in the world. Unfortunately, his ideas weren't entirely correct, but they're still taught in schools as a starting point of how modern chemistry was developed. Here were the five components of his original theory, with explanations of what he was wrong about.

1. All matter is composed of atoms.

Dalton got off to a good start with this statement- it's completely true.

2. All atoms of the same element have the same mass, size, and chemical properties.

This one isn't entirely true. The element of an atom is defined by its number of protons, but its mass depends on the amount of protons and neutrons. Two atoms of the same element can have a different number of neutrons, and therefore a different mass. Size and chemical reactivity are determined by amount of electrons, and ions, or charged atoms, of an element have different electron counts.

3. Atoms are the smallest possible unit of matter- they can't be split apart or created or destroyed.

We now know that this isn't true at all- atoms are composed of smaller particles, called protons, neutrons, and electrons. Even protons and neutrons are made of smaller particles called quarks.

4. Atoms of different elements can combine in simple whole number ratios to form compounds.

This is essentially a concise combination of two other scientific laws: the Law of Definite Proportions and the the Law of Multiple Proportions, and is entirely true.

5. This occurs through chemical reactions, where atoms are moved, rearranged, and form new bonds, but do not change elements.

Again, this is true- chemical reactions do not create or change atoms, just rearrange them.

Dalton's Atomic Theory

John Dalton:

Dalton's Atomic Theory

• A theory created by John Dalton, having to do with atoms (their properties and rules)

• Broken up into 5 key concepts:

In 1808, John Dalton proposed his atomic theory. There are 5 parts to his theory.

1. Elements are composed of incredibly small particles called atoms.
2. Atoms of the same element are exactly identical, and atoms of different elements are different.
3. Atoms cannot be divided, created, or destroyed.
4. Atoms of different elements combine in whole number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated, and rearranged.

With our modern understanding of science, we know that not all aspects of his atomic theory are true, but his findings were used by many scientists to further a lot of later research. We know that atoms of the same element are not exactly identical, there can be variations in the number of neutrons which affects the mass and other properties. Moreover, we know that atoms can be divided. In nuclear reactions, atoms can be split apart (fission) to form smaller atoms, or put together (fusion) to form larger atoms.

On the other hand, we have retained the most important parts of his theory in our modern understanding of chemistry. In a chemical reaction, atoms are combined, separated, and rearranged to form new compounds, and the atoms that compose these elements exist in whole number ratios. What this second statement means, is that a compound will never have a partial atom.