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460 BCE
Democritus (460 BCE - 370 BCE)
Democritus was born in Abdera, Greece. He studied natural philosphy, as well as geometry. Democritus is known as the father of modern atomic thought. He proposed the idea that matter could not be divided into smaller pieces and that it was composed of small particles called "atomos". According to him, atoms are solid but invisible, and also indestructible. He also said that they differ in size, shape, mass, and position. -
5 BCE
Leucippus
Known as the founder of atonism in ancient Greek philosiphy. There is not a lot of information about his life, but it is believed that he lived through the 5th century BCE. It is said that he was a student of Zeno of Elea. His relationship with Democritus is a subject of controversy. Leucippus is named as the originator of the theory that the universe consists of two different elements, which he called ‘the full’ and ‘the empty’. Both of this elements were said to be infinite -
John Dalton (1766 - 1844)
John Dalton was born into a quaker family in England. He worked as a teacher and was really interested in meteorology, which led to his view of atomism. He started calculating atomic weights and later in 1808, he came with his Atomic Theory, which said that elements consisted of tiny particles called atoms and that an element is one of a kind, because all atoms of an element are identical. He also said that compounds were formed by combining atoms. John Dalton also discovered color blindness. -
Eugene Goldstein (1850 - 1930)
A German physicist known for his work on electrical phenomena in gases and on cathode rays. In 1876 he discovered that these rays could cast sharp shadows, and that they were emitted perpendicular to the cathode surface. He is also known for discovering canal rays, in 1886. His interest was mainly in electrical discharges in moderate to high vacuums. Goldstein contributed a lot with his studies of cathode rays, later used for important experiments. -
J.J. Thomson (1856 - 1940)
He was born in a suburb of Manchester. Thompson was interested in the atomic structure. He was elected Fellow of the Royal Society in 1884. J.J. Thompson discovered electrons and noticed that an atom can be divided. He concluded that atoms are made of positive cores and negatively charged particles in it. Thompson made the Plum Pudding atomic model, in 1897, before the discovery of the atomic nucleus. Today, Thomson's discoveries have helped us have a better understanding of the atom. -
Ernest Rutherford (1871 - 1937)
Ernest Rutherford proposed the nuclear structure of the atom, in 1911. He also discovered alpha and beta rays, and proposed the laws of radioactive decay. He received the Nobel Prize of Chemistry in 1908. He discovered protons and the nucleus. He demonstrated that atoms have a (+) particles in the center and that they are mainly empty space. -
Niels Bohr (1885 - 1962)
Niels Bohr improved Rutherford's atomic model. He proposed that electrons moved around the nucleus in specific layers. He combined Rutherford's description of the nucleus and Planck's theory of the quanta to explain what really happens on an atom and to build the structure of it. Bohr's model shows the atom with a small and positively charged nucleus surrounded by a specific number of electron shells -
James Chadwick (1891 - 1974)
James Chadwick was an English physicist who discovered the neutron in 1932. He created a particular radiation by bombarding beryllium atoms with alpha particles. With the help of Rutherford's model, he discovered particles with no charge, and he called them neutrons.
