Historical Development of Atom

CONTENTS

1. FROM ALCHEMY TO CHEMISTRY

2. THE GREEK’S IDEA ABOUT THE ATOM

3. THE MODERN SCIENTISTS’ IDEA OF THE ATOM

4. THE NUCLEAR MODEL IN FOCUS

5. THE MAIN IDEAS IN THE DISCOVERY OF THE ATOMIC STRUCTURE AND ITS

SUBATOMIC PARTICLE

FROM ALCHEMY TO CHEMISTRY

The word “alchemy” brings to mind witches stirring a

boiling pot, or sorcerers in smoky labs. Despite these

magical images, alchemy led to how science is

practiced today.

Alchemy was an early philosophical and spiritual field

of study. It combined chemistry with metalwork. But it

also explored how nature works. Alchemy brought

together physics, medicine, astrology, mysticism,

spiritualism, and art.

The goals of alchemy were:

• to find the “elixir of life.” It was thought that this

magical potion would bring wealth, health, and

eternal life;

• to find or make a substance called the

“philosopher’s stone.” Alchemists thought gold was

the purest form of matter. They believed if they

combined the “stone” with copper or iron it would

create gold; and

• to discover the relationship of humans to the

cosmos. With that knowledge, alchemists wanted to

improve the human spirit.

Alchemy was scientific, but it was also spiritual. Some who practiced it had good hearts. Alchemists

wanted to learn the secret of “purifying” copper or iron into gold. If they could accomplish this, they

thought they might be able to purify the human soul. At the same time, alchemists were often seen as

fakes. But many alchemists were in fact serious about their work. What they accomplished helped lay

the building blocks for modern chemistry and medicine.

THE CENTRAL SCIENCE

Alchemy began as a quest to know the world around us. That quest for knowledge required an

understanding of how chemicals worked. Alchemy itself died out during the 1700s with the rise of

modern science. Yet, the quest it began continues today in chemistry. Chemistry is sometimes called

“the central science.” It connects sciences like physics, geology, and biology. To understand the field of

chemistry, we must start at the beginning.

Alchemists contributed to many future uses of chemicals like metalwork, paints and cosmetics. These

contributions enriched the societies in which alchemists lived. They even helped advance civilization.

But alchemists often saw no difference between their work with chemicals and what we might call

magic. They borrowed symbols and words from the Bible and myths. Even the simplest formula read

like a magic spell. And although there were commonly used practices, alchemists had no standards that

they all used.

FROM ALCHEMY TO CHEMISTRY

Chemistry Timeline

Ancient Alchemy 3000 B.C. to 800 A.D.

• c. 3000 B.C. – Egyptians formulate the theory of the Ogdoad, or the “primordial forces”, from which

all was formed. These were the elements of chaos that existed before the creation of the sun

• c. 1900 B.C. – Hermes Trismegistus, semi-mythical Egyptian king, who is supposed to have founded

of the art of alchemy

• c. 450 B.C. – Empedocles asserts that all things are composed of four primal elements – earth, air,

fire, and water, whereby two active and opposing forces, love and hate, or affinity and antipathy, act

upon these elements, combining and separating them into infinitely varied forms

• c. 440 B.C. – Democritus propose the idea of the atom, an indivisible particle that all matter is

made of • c. 360 B.C. – Plato coins term ‘elements’ and postulates that the minute particle of each

element had a special geometric shape – tetrahedron for fire; octahedron for air; icosahedron for

water; and cube for earth)

• c. 350 B.C. – Aristotle articulates his theory of the Five Elements, fire, water, earth, air, and ether

• 0 A.D. – Common Era after the Birth of Christ Begins

• c. 300 – Zosimos of Panopolis writes some of the oldest known books on alchemy

Classical Alchemy 800 A.D. to 1661

• c. 815 – Abu Musa Jabir ibn Hayyan isolates numerous acids, including hydrochloric acid, nitric

acid, citric acid, acetic acid, tartaric acid, and aqua regia

• c. 900 – Abū Bakr Muhammad ibn Zakarīya al-Rāzi publishes several treatises on chemistry,

including some of the earliest descriptions of controlled distillation and extraction methods

• c. 1220 – Robert Grosseteste publishes several Aristotelian commentaries where he lays out an

early framework for the scientific method

• c. 1267 – Roger Bacon publishes Opus Maius, proposing the scientific method and results of his

experiments with gunpowder

• c. 1530 – Paracelsus developes the study of iatrochemistry, a subdiscipline of alchemy dedicated to

extending the life

• 1597 – Andreas Libavius publishes Alchemia, a prototype chemistry textbook • 1605 – Sir Francis

Bacon publishes The Proficience and Advancement of Learning, containing an outline of the scientific

method

• 1605 – Michał Sędziwój publishes the alchemical treatise A New Light of Alchemy, proposing the

existence of the "food of life" within air

• 1615 – Jean Beguin publishes the early chemistry textbook, Tyrocinium Chymicum, with the first-

ever chemical equation

• 1637 – René Descartes publishes Discours de la Méthode, containing an outline of the scientific

method

• 1648 – Publication of the Johann Baptista van Helmont’s book Ortus Medicinae a major transitional

work between alchemy and chemistry, and which also influences Robert Boyle. The book shows the

results of experiments and establishes an early version of the Law of Conservation of Mass

FROM ALCHEMY TO CHEMISTRY

The Modern Chemistry Era 1661 to Present

• 1661 – Robert Boyle publishes The Sceptical Chymist, a treatise on the distinction between

chemistry and alchemy

• 1662 – Robert Boyle proposes Boyle's Law on the behavior of gases

• 1754 – Joseph Black isolates carbon dioxide

• 1758 – Joseph Black formulates the concept of latent heat to explain the thermochemistry of

phase changes

• 1773-1774 – Carl Wilhelm Scheele and Joseph Priestly independantly isolate oxygen

• 1778 – Antoine Lavoisier recognizes and names oxygen, and recognizes its importance and

role in combustion

• 1787 – Antoine Lavoisier publishes Méthode de Nomenclature Chimique, the first modern

system of chemical nomenclature

• 1787 – Jacques Charles proposes a corollary to Boyle’s Law, which he names Charles's Law,

describing the relationship between temperature and volume of a gas

• 1789 – Antoine Lavoisier publishes the first modern chemistry textbook, Traité Élémentaire

de Chimie

• 1797 – Joseph Proust proposes Law of Definite Proportions, which states that elements

always combine in small, whole number ratios to form compounds

• 1800 – Alessandro Volta makes the first chemical battery

• 1803 – John Dalton proposes Dalton's Law, which describes relationship between the

components in a mixture of gases and the relative pressure each contributes to that of the

overall mixture

• 1805 – Joseph Louis Gay-Lussac discovers that water is composed of two parts hydrogen

and one part oxygen

• 1807-1808 – Sir Humphry Davy uses electrolysis to isolate numerous elements, including

potassium, sodium, calcium, strontium, barium, chlorine and the first discovery of aluminum

• 1808 – John Dalton publishes New System of Chemical Philosophy, which contains first

modern scientific description of the atomic theory

• 1808 – Jöns Jakob Berzelius publishes Lärboki Kemien in which he proposes modern

chemical symbols and notation, and of the concept of relative atomic weight

• 1811 – Amedeo Avogadro proposes Avogadro's law, that equal volumes of gases contain

equal numbers of particles

• 1825 – Michael Faraday isolates benzene

• 1828 – Friedrich Wöhler synthesizes urea, thereby establishing that organic compounds

could be produced from inorganic starting materials, disproving the theory of “vital life force”

• 1840 – Germain Hess proposes Hess's Law, an early statement of the Law of conservation of

energy

• 1847 – Hermann Kolbe obtains acetic acid from completely inorganic sources • 1848 – Lord

Kelvin establishes concept of absolute zero, the temperature at which all molecular motion

ceases

• 1849 – Louis Pasteur discovers chirality and in tartaric acid, starting the study of

stereochemistry

• 1855 – Benjamin Silliman, Jr. pioneers methods of petroleum cracking, which makes the

entire modern petrochemical industry possible

FROM ALCHEMY TO CHEMISTRY

• 1856 – William Henry Perkin synthesizes the first synthetic dye

• 1862 – Alexander Parkes exhibits Parkesine, one of the earliest synthetic polymers

• 1865 – Friedrich August Kekulé von Stradonitz establishes structure of benzene as a six carbon ring

• 1865 – Adolf von Baeyer begins work on indigo dye, a milestone in modern industrial organic chemistry

which revolutionizes the dye industry

• 1869 – Dmitri Mendeleev publishes the first modern periodic table

• 1883 – Svante Arrhenius developes ion theory to explain conductivity in electrolytes

• 1884 – Henry Louis Le Chatelier develops Le Chatelier's principle, which explains the response of

dynamic chemical equilibria to external stresses

• 1894-1898 – William Ramsay discovers the noble gases

• 1903 – Mikhail Semyonovich Tsvet invents chromatography

• 1905 – Fritz Haber and Carl Bosch develop the Haber process for making ammonia

• 1907 – Leo Hendrik Baekeland inventes bakelite, one of the first commercially successful plastics

• 1909 – Ernest Rutherford, Hans Geiger, and Ernest Marsden perform the Gold foil experiment, which

proves the nuclear model of the atom, with a small, dense, positive nucleus surrounded by a diffuse

electron cloud

• 1909 – Robert Millikan performs the Oil drop experiment, which confirms the existence of electron as

the quanta of electric charge, and determines charge/mass ratio of an electron

• 1909 – S. P. L. Sørensen invents the pH concept and develops methods for measuring acidity • 1912 –

William Henry Bragg and William Lawrence Bragg proposes Bragg's law and establishes the field of X-ray

crystallography

• 1913 – Niels Bohr introduces concepts of quantum mechanics to atomic structure by proposing what is

now known as the Bohr model of the atom

• 1913 – Frederick Soddy proposes the concept of isotopes, that elements with the same chemical

properties may have differing atomic weights

• 1916 – Gilbert N. Lewis publishes The Atom and the Molecule, the foundation of valence bond theory

• 1921 – Otto Stern and Walther Gerlach establish concept of quantum mechanical spin in subatomic

particles

• 1923 – Gilbert N. Lewis and Merle Randall publish Thermodynamics and the Free Energy of Chemical

Substances, first modern treatise on chemical thermodynamics

• 1923 – Gilbert N. Lewis develops the electron pair theory of acid/base reactions

• 1935 – Wallace Carothers leads a team of chemists at DuPont who invent nylon

• 1932 – Linus Pauling first describes the property of electronegativity as a means of predicting the dipole

moment of a chemical bond

• 1937 – Carlo Perrier and Emilio Segrè perform the first confirmed synthesis of technetium-97, the first

artificially produced element

• 1937 – Eugene Houdry develops a method of industrial scale catalytic cracking of petroleum, leading to

the development of the first modern oil refinery

• 1939 – Linus Pauling publishes The Nature of the Chemical Bond, one of the most important modern

chemical texts

• 1945-1946 – Felix Bloch and Edward Mills Purcell develop the process of Nuclear Magnetic Resonance,

an analytical technique important in elucidating structures of molecules, especially in organic chemistry

• 1952 – Robert Burns Woodward, Geoffrey Wilkinson, and Ernst Otto Fischer discover the structure of

ferrocene, one of the founding discoveries of the field of organometallic chemistry • 1962 – Neil Bartlett

synthesizes xenon hexafluoroplatinate, showing for the first time that the noble gases can form chemical

compounds

• 1985 – Harold Kroto, Robert Curl and Richard Smalley discover fullerenes, a class of large carbon

molecules superficially resembling the geodesic dome designed by architect R. Buckminster Fuller

• 1995 – Eric Cornell and Carl Wieman produce the first Bose–Einstein condensate, a substance that

displays quantum mechanical properties on the macroscopic scale

THE GREEK’S IDEA ABOUT THE ATOM

ARISTOTLE and PLATOAristotle was a very famous Greek philosopher whobelieved that matter could be divided into smaller andsmaller pieces forever. He held a very strong influence onpopular belief and his views on this were accepted for twothousand years. Aristotle and Plato favored the earth,

fire, air and water approach to the nature of matter.

He thought matter is like motion.

It cannot be divided in half forever.

The tortoise and hare would never finish the race if you could keep

dividing the distance to the finish line in half forever.

LEUCIPPUS AND DEMOCRITUS

Democritus was an ancient Greek philosopher who lived from 460 - 370 B.C.

His teacher was Leucippus.

What did Democritus and Leucippus conclude about cutting matter in half?

There was a limit to how far you could divide matter. You would eventually

end up with a piece of matter that could not be cut which he termed as

“atomos” – uncuttable and indestructible.

To Democritus, atoms were small, hard particles that were all made of the same

material but were different shapes and sizes. Atoms were infinite in number, always

moving and capable of joining together.

This theory was ignored and forgotten for more than 2000 years!!! Why?

The eminent philosophers of the time, Aristotle and Plato, had a more respected, (and

ultimately wrong) theory.

EMPEDOCLESAristotle was a very famous Greek philosopher whobelieved that matter could be divided into smaller andsmaller pieces forever. He held a very strong influence onpopular belief and his views on this were accepted for twothousand years. Aristotle and Plato favored the earth,

fire, air and water approach to the nature of matter.

THE MODERN SCIENTISTS’ IDEA OF THE ATOM

Dalton expressed his theory in a series of postulates. Like most great thinkers, he

integrated the ideas of others into his own.

1. All matter consists of atoms, tiny indivisible particles of an element that cannot be

created nor destroyed. (This is derived from the “eternal, indestructible atoms”

proposed by Democritus more than 2000 years earlier and reflects mass

conservation as stated by Lavoisier)

2. Atoms of one element cannot be converted into atoms of another element, In

chemical reactions, the atoms of the original substances recombine to form

different substances. (This rejects the belief in the magical transmutation of

elements that was widely held into the 17th century.)

3. Atoms of an element are identical in mass and other properties and are different

from atoms of any other element. (This contains Dalton’s major new ideas: unique

mass ad properties for the atoms of a given element.)

4. Compounds result from the chemical combination of a specific ration of atoms of

different elements. (This follows directly from the law of definite composition.)

JOHN DALTONTwo thousand years later a British chemist and schoolteacher brings back

Democritus’s idea of the atom. He performed many experiments to study how

elements join together to form new substances. He found that they combine in

specific ratios (remember the electrolysis of water) and he supposed it was

because the elements are made of atoms.

JOSEPH JOHN THOMSONIn 1897, the English scientist J.J. Thomson provided the first hint that an atom is

made of even smaller particles. He proposed a model of the atom called the

“Raisin Bread/Bun Model” that is sometimes called the “Plum Pudding” model.

Atoms were made from a positively charged substance with negatively charged

electrons scattered about, like raisins in a pudding.

Thomson concluded that the negative charges came from

within the atom. A particle smaller than an atom had to exist.

The atom was divisible!

Thomson studied the passage of an electric current

through a gas. As the current passed through the gas, it

gave off rays of negatively charged particles.

This surprised Thomson, because the atoms of the gas were

uncharged. Where had the negative charges come from?

Thomson called the negatively charged “corpuscles,” today known as electrons.

Since the gas was known to be neutral, having no charge, he reasoned that there must

be positively charged particles in the atom. But he could never find them.

THE MODERN SCIENTISTS’ IDEA OF THE ATOM

ERNEST RUTHERFORDIn 1908, the English physicist Ernest Rutherford was hard at work on an

experiment that seemed to have little to do with unraveling the mysteries of the

atomic structure.

Rutherford’s experiment involved firing a stream of tiny positively charged

particles at a thin sheet of gold foil (2000 atoms thick).

This could only mean that

the gold atoms in the

sheet were mostly open

space. Atoms were not a

pudding filled with a

positively charged

material. Rutherford

concluded that an atom

had a small, dense,

positively charged center

that repelled his positively

charged “bullets.”

He called the center of the

atom the “nucleus”

The nucleus is tiny

compared to the atom as

a whole.

Most of the positively charged “bullets” passed right through the

gold atoms in the sheet of gold foil without changing course at

all. Some of the positively charged “bullets,” however, did bounce

away from the gold sheet as if they had hit something solid. He

knew that positive charges repel positive charges.

Rutherford reasoned that all of an atom’s positively charged

particles were contained in the nucleus. The negatively charged

particles were scattered outside the nucleus around the atom’s

edge. His proposed model of the atom is called the “nuclear model”.

NEILS BOHRIn 1913, the Danish scientist Niels Bohr proposed an

improvement. In his model, he placed each electron in

a specific energy level.

According to Bohr’s atomic model, “Planetary Model”,

electrons move in definite orbits around the nucleus,

much like planets circle the sun. These orbits, or

energy levels, are located at certain distances from

the nucleus.

THE NUCLEAR MODEL IN FOCUS

RUTHERFORD’SNUCLEAR MODEL OF AN ATOM

Mostly empty space

Small, positive nucleus

Contained protons

Negative electrons scattered around the

outside

Subatomic Particles Location

ElectronsOutside nucleus

(energy levels)

Protons Nucleus

Neutrons Nucleus

THE MAIN IDEAS IN THE DISCOVERY OF THE ATOMIC STRUCTURE

AND ITS SUBATOMIC PARTICLEThe idea of atom, “atomism”, was first proposed by the ancient Greek philosopher

Democritus. His idea was ignored for about 2000 years because the idea of eminent philosophers,

Aristotle and Plato, was favored due to their influence on public belief.

Democritus was justified by John Dalton by adopting his idea and proposed the

atomic theory. The first model of the atom, the “Solid Sphere Model”, was proposed by Dalton. He

opened the revolution on the study of atom. There were more atomic theories proposed and the

development of the atomic structure persisted.

Consequently, Joseph John Thomson discovered the electron by working in an

experiment involving the use of cathode ray tube. With this, he was able to propose his own model

of the atom, the “Plum Pudding Model” or the “Raisin Bun/Bread Model”.

After the discovery of electron, the nucleus was discovered by Ernest Rutherford

through the gold-foil experiment which involved firing a stream of tiny positively charged particles at

a thin sheet of gold foil (2000 atoms thick). His model of the atom is called “Nuclear Model”.James Chadwick discovered the neutron using evidence collected by Irene Joliot-Curie, who

discovered that when beryllium was bombarded with positively charged alpha particles a beam with a highpenetrating power was created. James Chadwick discovered that this beam was not deflected by eitherelectric or magnetic fields, meaning it contained neutral particles- neutrons. Neutrons were found to havethe same mass as protons which accounted for more of the mass of the atom and allowed the masses (theknownmass of an atom and the knownmass of its particles) to match.

The common understanding of an atom was now a nucleus containing positively chargedprotons and neutral neutrons (making up nearly all of the atom's mass) with the rest of the atom (most of it-considering the relative size of the nucleus, which was found to have a radius of10000 times less than theatom itself) being space in which negatively charged electrons (with a mass so small it is insignificantcompared to that of the nucleus) "orbit" the nucleus on energy levels corresponding to the amount of energythe electrons hold.

REFERENCES:

• https://www.ambrosevideo.com/resources/documents/Timeline%20for%20Core%20Ch

emistry.pdf

• https://school.bighistoryproject.com/media/khan/articles/U3_From_Alchemy_to_Chemi

stry_2014_810Lindd.pdf

• https://sites.google.com/site/historyofanatom/james-chadwick

• http://www.chymist.com/History%20Alchemy.pdf