Name: dalton’s laws and early atomic ideas
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 2 min 59 s
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Chemistry

Matter and its Interactions

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The Atomic Theory of Matter

Early Greeks like Democritus first advanced the idea of atomos, the smallest indivisible unit of matter. This concept was later put forth as the atomic theory by the English scientist John Dalton. &nbsp;

The first postulate of Dalton&rsquo;s atomic theory suggests that elements are composed of tiny indivisible particles called atoms. For example, hydrogen is made up of two hydrogen atoms bonded together and oxygen is made up of two oxygen atoms bonded together.

The second postulate states that while atoms of the same element are identical, they differ from the atoms of other elements. Thus, all the atoms of hydrogen are identical to each other, but differ from oxygen atoms. &nbsp;

The third postulate states that atoms of different elements may combine with each other, in simple whole-number ratios, to form compounds. For example, two atoms of hydrogen and one atom of oxygen combine in a 2 to 1 ratio to form H2O &mdash; water.&nbsp;

The last postulate of Dalton&rsquo;s theory states that chemical reactions do not change the atoms of one element into atoms of a different element; instead, the existing atoms rearrange themselves to form new substances. During the formation of water, existing hydrogen and oxygen atoms are neither created nor destroyed, they only rearrange.&nbsp;

Dalton built his atomic theory upon two previous laws of chemical reactions:&nbsp;the law of conservation of mass and the law of definite proportions.

The law of conservation of mass states that the total mass before and after a chemical reaction remains constant. So, 18 g of water breaks down into 2 g of hydrogen and 16 g of oxygen.

The law of definite proportions states that independent of the source, in a given chemical compound, the mass ratio of constituent elements always remains fixed. Thus, a sample of pure water will always have a 1 to 8 mass ratio of hydrogen to oxygen irrespective of the total mass of the water.

Dalton then proposed the law of multiple proportions based on his own theory. According to this law, when two elements combine to form more than one compound, different masses of one element combine with the fixed mass of the other element in a small whole-number ratio.&nbsp;

Thus, a fixed mass of hydrogen, 2 g, combines with different masses of oxygen, 32 or 16 g, in a small whole-number ratio of 2 to 1, to form two different compounds &mdash; hydrogen peroxide, and water.&nbsp;

the atomic theory of matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter was composed of small, finite particles that they called atomos, meaning &ldquo;indivisible.&rdquo; Later, Aristotle and others came to the conclusion that matter consisted of various combinations of the four &ldquo;elements&rdquo; &mdash; fire, earth, air, and water &mdash; and could be infinitely divided. Interestingly, these philosophers thought about atoms and &ldquo;elements&rdquo; as philosophical concepts, but apparently never considered performing experiments to test their ideas.&nbsp;

The Aristotelian view of the composition of matter held sway for over two thousand years until English scientist John Dalton revolutionized chemistry with his hypothesis that the behavior of matter could be explained using an atomic theory. First published in 1807, many of Dalton&rsquo;s hypotheses about the microscopic features of matter are still valid in modern atomic theory.&nbsp;

Here are the postulates of Dalton&rsquo;s atomic theory:

<ol>
	<li>Matter is composed of exceedingly small particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change.</li>
	<li>An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element. A macroscopic sample of an element contains an incredibly large number of atoms, all of which have identical chemical properties.</li>
	<li>Atoms of one element differ in properties from atoms of all other elements.</li>
	<li>A compound consists of atoms of two or more elements combined in a small, whole-number ratio. In a given compound, the numbers of atoms of each of its elements are always present in the same ratio</li>
	<li>Atoms are neither created nor destroyed during a chemical change but are instead rearranged to yield substances that are different from those present before the change.</li>
</ol>

Dalton used three laws of chemical reactions as a basis for his theory: (1) The Law of Conservation of Mass, (2) The Law of Definite Proportions, and (3) The Law of Multiple Proportions. Dalton&rsquo;s atomic theory provides a microscopic explanation of the many macroscopic properties of matter.&nbsp;

The law of conservation of mass was discovered by the French chemist, Antoine Lavoisier. It states that atoms are neither created nor destroyed during a chemical change; the total mass of matter present when matter changes from one type to another remains constant.

Dalton also knew of the experiments of French chemist Joseph Proust, who demonstrated that all samples of a pure compound contain the same elements in the same proportion by mass. This statement is known as the law of definite proportions or the law of constant composition. The suggestion that the numbers of atoms of the elements in a given compound always exist in the same ratio is consistent with these observations.&nbsp;

Dalton also used data from Proust, as well as results from his own experiments, to formulate another interesting law. The law of multiple proportions states that when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other elements in a ratio of small, whole numbers.

Dalton&rsquo;s theory provided a framework that was later expanded to demonstrate that the atom is composed of subatomic particles and that atoms of the same element can differ in mass, known as isotopes.

This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/2-1-early-ideas-in-atomic-theory">Openstax, Chemistry 2e, Section 2.1: Early Ideas in Atomic Theory.</a> &nbsp;

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

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dalton’s laws and early atomic ideas

Dalton’s atomic theory explains matter with atoms, elements, and compounds. It also shows how chemical changes follow simple laws. This idea gave chemistry a microscopic model for what can be seen in the lab.

The earliest recorded ideas about matter came from ancient Greek philosophers. Leucippus and Democritus said all matter was made of tiny, finite particles called atomos, meaning “indivisible.” Aristotle and others later argued that matter was made from four elements: fire, earth, air, and water. They also believed matter could be divided forever, and these ideas were treated as philosophy rather than experiments.

That view lasted for more than two thousand years. Then English scientist John Dalton changed chemistry with an atomic theory of matter. He first published it in 1807. Many of his ideas still fit modern atomic theory.

Dalton’s postulates describe matter at the atomic level. Matter is made of extremely small particles called atoms. An atom is the smallest unit of an element that can take part in a chemical change. An element contains only one type of atom, and atoms of the same element have the same characteristic mass and chemical properties. Atoms of different elements have different properties. A compound is made of atoms of two or more elements joined in a small, whole-number ratio, and the ratio stays the same in a given compound. During a chemical change, atoms are not created or destroyed. They are rearranged into new substances.

Dalton built his theory using three key laws of chemistry. The law of conservation of mass says mass stays constant during a chemical change, a result linked to Antoine Lavoisier. The law of definite proportions, also called the law of constant composition, says every pure sample of a compound contains the same elements in the same mass ratio, as shown by Joseph Proust. Dalton also used the law of multiple proportions, which says that when two elements form more than one compound, fixed masses of one element combine with the other in small whole-number ratios.

Dalton’s atomic theory gives a microscopic explanation for macroscopic matter. It also helped later scientists show that atoms contain subatomic particles. Later work also showed that atoms of the same element can differ in mass, which are called isotopes.

Dalton’s Laws and Early Atomic Ideas

Dalton’s atomic theory explains matter with atoms, elements, and compounds. It also shows how chemical changes follow simple laws. This idea gave chemistry a microscopic model for what can be seen in the lab. The earliest recorded ideas about matter came from ancient Greek philosophers. Leucippus and Democritus said all matter was made of tiny, finite particles called atomos, meaning “indivisible.” Aristotle and others later argued that matter was made from four elements: fire, earth, air, and...

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key terms and concepts

Explore Dalton’s atomic theory, the laws of conservation of mass, definite proportions, and multiple proportions, plus the early ideas that shaped modern chemistry.

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Dalton’s Laws and Early Atomic Ideas

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