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Learning Objectives
- Give a short history of the concept of the atom.
- Describe the contributions of Democritus and Dalton to atomic theory.
- Summarize Dalton's atomic theory and explain its historical development.
You learned earlier that all matter in the universe is made out of tiny building blocks called atoms. All modern scientists accept the concept of the atom, but when the concept of the atom was first proposed about 2,500 years ago, ancient philosophers laughed at the idea. It has always been difficult to convince people of the existence of things that are too small to see. We will spend some time considering the evidence (observations) that convince scientists of the existence of atoms.
Democritus and the Greek Philosophers
About 2,500 years ago, early Greek philosophers believed the entire universe was a single, huge, entity. In other words, "everything was one." They believed that all objects, all matter, and all substances were connected as a single, big, unchangeable "thing." One of the first people to propose "atoms" was a man known as Democritus. As an alternative to the beliefs of the Greek philosophers, he suggested that atomos, or atomon—tiny, indivisible, solid objects—make up all matter in the universe.
Democritus then reasoned that changes occur when the many atomos in an object were reconnected or recombined in different ways. Democritus even extended this theory, suggesting that there were different varieties of atomos with different shapes, sizes, and masses. He thought, however, that shape, size, and mass were the only properties differentiating the different types of atomos. According to Democritus, other characteristics, like color and taste, did not reflect properties of the atomos themselves, but rather, resulted from the different ways in which the atomos were combined and connected to one another.
The early Greek philosophers tried to understand the nature of the world through reason and logic, but not through experiment and observation. As a result, they had some very interesting ideas, but they felt no need to justify their ideas based on life experiences. In a lot of ways, you can think of the Greek philosophers as being "all thought and no action." It's truly amazing how much they achieved using their minds, but because they never performed any experiments, they missed or rejected a lot of discoveries that they could have made otherwise. Greek philosophers dismissed Democritus' theory entirely. Sadly, it took over two millennia before the theory of atomos (or "atoms," as they are known today) was fully appreciated.
Greeks: "All Thought and No Action"
Greek philosophers were "all thought and no action" and did not feel the need to test their theories with reality. In contrast, Dalton's efforts were based on experimentation and testing ideas against reality.
While it must be assumed that many more scientists, philosophers, and others studied composition of matter after Democritus, a major leap forward in our understanding of the composition of matter took place in the 1800's with the work of the British scientists John Dalton. He started teaching school at age twelve, and was primarily known as a teacher. In his twenties, he moved to the growing city of Manchester, where he was able to pursue some scientific studies. His work in several areas of science brought him a number of honors. When he died, over 40,000 people in Manchester marched at his funeral.
The modern atomic theory, proposed about 1803 by the English chemist John Dalton (Figure \(\PageIndex{1}\)), is a fundamental concept that states that all elements are composed of atoms. Previously, we defined an atom as the smallest part of an element that maintains the identity of that element. Individual atoms are extremely small; even the largest atom has an approximate diameter of only 5.4 × 10−10 m. With that size, it takes over 18 million of these atoms, lined up side by side, to equal the width of your little finger (about 1 cm).
Dalton studied the weights of various elements and compounds. He noticed that matter always combined in fixed ratios based on weight, or volume in the case of gases. Chemical compounds always contain the same proportion of elements by mass, regardless of amount, which provided further support for Proust's law of definite proportions. Dalton also observed that there could be more than one combination of two elements.
From his experiments and observations, as well as the work from peers of his time, Dalton proposed a new theory of the atom. This later became known as Dalton's atomic theory. The general tenets of this theory were as follows:
- All matter is composed of extremely small particles called atoms.
- Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties.
- Atoms cannot be subdivided, created, or destroyed.
- Atoms of different elements can combine in simple whole number ratios to form chemical compounds.
- In chemical reactions, atoms are combined, separated, or rearranged.
Dalton's atomic theory has been largely accepted by the scientific community, with the exception of three changes. We know now that (1) an atom can be further subdivided, (2) all atoms of an element are not identical in mass, and (3) using nuclear fission and fusion techniques, we can create or destroy atoms by changing them into other atoms.
The evidence for atoms is so great that few doubt their existence. In fact, individual atoms are now routinely observed with state-of-the art technologies. Moreover, they can even be used for making pretty images; or as IBM research demonstrates in Video \(\PageIndex{1}\), control of individual atoms can be use used create animations.
A Boy and His Atom is a 2012 stop-motion animated short film released by IBM Research. The movie tells the story of a boy and a wayward atom who meet and become friends. It depicts a boy playing with an atom that takes various forms. It was made by moving carbon monoxide molecules viewed with a scanning tunneling microscope, a device that magnifies them 100 million times. These molecules were moved to create images, which were then saved as individual frames to make the film.
Summary
- 2,500 years ago, Democritus suggested that all matter in the universe was made up of tiny, indivisible, solid objects he called "atomos." However, other Greek philosophers disliked Democritus' "atomos" theory because they felt it was illogical.
- Dalton's Atomic Theory is the first scientific theory to relate chemical changes to the structure, properties, and behavior of the atom. The general tenets of this theory are:
- All matter is composed of extremely small particles called atoms.
- Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties.
- Atoms cannot be subdivided, created, or destroyed.
- Atoms of different elements can combine in simple whole number ratios to form chemical compounds.
- In chemical reactions, atoms are combined, separated, or rearranged.
FAQs
What is the theory of an indivisible atom? ›
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.
Why does Democritus said that the atom is indivisible? ›His famous disciple, Democritus of Abdera, named the building blocks of matter atomos, meaning literally “indivisible,” about 430 bce. Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped.
What are the 4 principles of the atomic theory? ›1) All matter is made of atoms. Atoms are indivisible and indestructible. 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms.
Who said dude believe me atoms are indivisible and Cannot be created nor destroyed? ›John Dalton. Experiments with gases that first became possible at the turn of the nineteenth century led John Dalton in 1803 to propose a modern theory of the atom based on the following assumptions. 1. Matter is made up of atoms that are indivisible and indestructible.
Who proposed that atom is indivisible? ›John Dalton proposed the theory that atom is indivisible. He considered atom to be the smallest part of matter and which cannot be further divided.
What disproved that atoms are indivisible? ›Limitations of Dalton's Atomic Theory
It does not account for subatomic particles: Dalton's atomic theory stated that atoms were indivisible. However, the discovery of subatomic particles (such as protons, electrons, and neutrons) disproved this postulate.
All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed.
Do you agree that atoms are indivisible? ›Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms.
Who came up with 4 main ideas of atomic theory? ›Dalton proposed his atomic theory in 1804. The general tenets of this theory are: All matter is composed of extremely small particles called atoms.
How can I explain the atomic theory? ›Atomic theory states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. It began as a philosophical concept in ancient Greece (Democritus) and India and entered the scientific mainstream in the early 19th century.
Who developed 4 rules for atomic theory? ›
A theory of chemical combination, first stated by John Dalton in 1803. It involves the following postulates: (1) Elements consist of indivisible small particles (atoms).
Why didn t anyone believe Democritus ideas about atoms? ›Early Greek philosophers disliked Democritus' theory of atomos because they believed a void, or complete "nothingness", was illogical. To ancient thinkers, a theory that went against "logic" was far worse than a theory that went against experience or observation.
What was Aristotle's beliefs about atoms? ›Aristotle did not believe that matter was made up of tiny particles called atoms, but rather matter up of five basic elements, earth, water, air, fire, and ether. Although Aristotle's idea wasn't correct, his idea was more widely accepted than Democritus's idea from about 2000 years.
What did Einstein say about atoms? ›Einstein also in 1905 mathematically proved the existence of atoms, and thus helped revolutionize all the sciences through the use of statistics and probability. Atomic theory says that any liquid is made up of molecules (invisible in 1905). Furthermore, these molecules are always in random, ceaseless motion.
Did Thomson think atoms were indivisible? ›Some scientists gathered in the hall admitted later to Thomson that they thought he was “pulling their legs”. It was firmly believed then that the atom was indivisible. Even the word 'atom', with its Greek root word atomos, means indivisible.
Do indivisible particles exist? ›Atoms, however, do not have an independent existence, in general. They generally exist in combination with other atoms in the form of molecules or ions.
What particle means indivisible? ›C, Democritus postulated that matter is made up of very small particles called “atoms” which means"indivisible".
When did Democritus describe atoms as indivisible particles? ›In 400 B.C., the Greek philosopher Democritus proposed that all matter was made of tiny indivisible particles, which he named atomos.
What does indivisible mean in science? ›Something indivisible cannot be broken up or divided: it's rock solid.
Why are atoms called indivisible particles? ›Atom is an indivisible particle. Atoms can neither be created nor be destroyed. Atoms of an element are identical in size, shape, mass and in other properties. Atoms of different elements are different in their properties.
What are the 5 atomic theories? ›
- Ancient Greek Beliefs. ...
- Dalton's Atomic Theory. ...
- J.J. ...
- Rutherford's Hypothesis. ...
- Bohr's Theory. ...
- Einstein, Heisenberg and Quantum Mechanics.
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.
Is the atomic theory proven? ›Viewpoint: No, many pre-twentieth-century scientists, lacking any direct evidence of the existence of atoms, concluded that atoms are not real. Today the reality of the atom is taken for granted. Pictures taken by tunnelling electron microscopes can even "show" individual atoms.
Why is atomic theory so important? ›Atomic theory established that all matter is made of tiny particles, a discovery that led to amazing scientific breakthroughs in areas from modern chemistry to nuclear energy.
Is the atomic theory a fact? ›Atomic theory is the description of atoms , the smallest units of elements. The scientific evidence for the existence of atoms and its even smaller constituents is so vast that most people now consider the existence of atoms to be a fact and not just a theory.
How do we know atoms exist? ›How do we know they exist? Through chemical reactions we can witness their effects. Through mathematical equations combined with indirect observations, we can calculate their various sizes. And finally, with the aid of new technologies such as the Scanning Tunnelling Microscope, atoms can now be seen.
What are the four major points of Dalton's atomic theory? ›Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction. Atoms of a given element are identical in mass and chemical properties. Atoms of different elements have different masses and chemical properties. Atoms combine in the ratio of small whole numbers to form compounds.
Who disproved Democritus theory? ›Although Democritus' theory was remarkable, it was rejected by Aristotle, one of the most influential philosophers of Ancient Greece; and the atomic theory was ignored for nearly 2,000 years.
Why did Democritus not believe in God? ›Democritus regarded the freedom of the individual as more important than the needs of the state. Democritus did not believe in God or the gods, believing the world to be governed entirely by natural laws. This may be one of the reasons his works perished in later years. Democritus lived a long life, probably 90 years.
Are Democritus ideas still accepted today? ›Are Democritus' theories of atoms still relevant today? Well, yes, sort of. Democritus had no instruments to extend the reach of his senses, so all of his experiments were just "mind experiments." The ancient Greeks gave humanity tremendous gifts despite only having their minds to work with.
Which philosopher did not believe in atoms? ›
Democritus was an important philosopher, but he was less influential than another Greek philosopher named Aristotle, who lived about 100 years after Democritus. Aristotle rejected Democritus' idea of the atom. In fact, Aristotle thought the idea was ridiculous.
What was Aristotle's atomic theory called? ›Although today's modern "atomic theory" is based on the "atomos" theory; the "Earth, air, fire, and water" theory was the accepted theory for over 2000 years. This is because Aristotle proclaimed his support for the "Earth, air, fire and water" model!
What is the reason why Aristotle rejected the idea of atomism? ›Rejection in Aristotelianism
Aristotle considered the existence of a void, which was required by atomic theories, to violate physical principles. Change took place not by the rearrangement of atoms to make new structures, but by transformation of matter from what it was in potential to a new actuality.
There is no such thing as water atoms. Water molecules are made of hydrogen and oxygen atoms, in the definite proportion of two hydrogens for one oxygen. Hence, a molecule is the smallest subunit of a compound while an atom is the smallest subunit of an element.
Who first said that atoms exist? ›The Greek philosopher Democritus (460-370B. C.) conjectured that all things were composed of small, indivisible bits called "atoms," rendered from the Greek atomos meaning "indivisible." Democritus' atoms came in different sizes and could combine or separate.
How did Einstein prove the existence of the atom? ›Albert Einstein proved the existence of atoms by establishing equations showing and predicting the motion of particles in liquid. In 1827, the discovery of movement on particles by Robert Brown on a microscope was a scientific mystery.
Can a human split an atom? ›Scientists split atoms in order to study atoms and the smaller parts they break into. This is not a process that can be carried out at home. You can only do nuclear fission in a laboratory or nuclear plant that is properly equipped.
What is Dalton's atomic theory? ›Dalton's Atomic Theory (1804)
All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed.
To prove that atoms existed he conducted an experiment in which he divided a seashell into its smallest component parts. Democritus stated that atomism is the induction that all matter is made of basic building blocks that are unbreakable in nature. He used the terms Being and The Void to describe the world.
Did JJ Thomson think atoms were indivisible? ›In 1897, J. J. Thomson dramatically changed the modern view of the atom with his discovery of the electron. Thomson's work suggested that the atom was not an "indivisible" particle as John Dalton had suggested but a jigsaw puzzle made of smaller pieces.
What is universe atom theory? ›
Democritus taught the theory of atomism, which held the belief that indivisible and indestructible atoms are the basic components of all matter in the universe. Thus the word atom is derived from the Greek atomos meaning indivisible.
What are Dalton's 3 Rules of atomic theory? ›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.
Who disproved Democritus atomic theory? ›Although Democritus' theory was remarkable, it was rejected by Aristotle, one of the most influential philosophers of Ancient Greece; and the atomic theory was ignored for nearly 2,000 years.
Did Democritus discover the atom? ›One of the earliest records we have on the atom came from Democritus, an ancient Greek philosopher (others like Plato and Aristotle had similar trains of thought). Democritus had a thought experiment. The idea was if you took a material and divided it half, you would have a smaller but identical chunk.
How did Democritus change the atomic theory? ›What is Democritus known for? Democritus was a central figure in the development of the atomic theory of the universe. He theorized that all material bodies are made up of indivisibly small “atoms.” Aristotle famously rejected atomism in On Generation and Corruption.