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. Atoms of different elements differ in size, mass, and other properties.

Around 400 B.C.E., the Greek philosopher Democritus introduced the idea of the atom as the basic building block matter. Democritus thought that atoms are tiny, uncuttable, solid particles that are surrounded by empty space and constantly moving at random.

Explain why Democritus was unable to experimentally verify his ideas. Democritus was unable to explain his ideas because he didn’t have the resources he need to prove the existence of atoms. Aristotle believed that there was no empty space, therefore atoms could not move through empty space.

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.

Democritus (Greek: Δημόκριτος) was an ancient Greek philosopher. He was born in Thrace, Greece, circa 460 BC. He was a rich citizen of Abdera, in Thrace, and a student of Leucippus, another Greek philosopher.

Democritus did not believe in God or the gods, believing the world to be governed entirely by natural laws. Some ancient sources claim he lived longer: the third century AD Greek biographer Diogenes Laërtius said Democritus lived for 109 years.

Dalton’s atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass.

Terms in this set (5)

• Elements are composed of extremely small particles called atoms that are indivisible and indestructible.
• All atoms of a given element are identical; they have the same size, mass, and chemical properties.
• Atoms of 1 element are different from the atoms of all other elements.

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.

Ernest Rutherford’s most famous experiment is the gold foil experiment. A beam of alpha particles was aimed at a piece of gold foil. Most alpha particles passed through the foil, but a few were scattered backward. This showed that most of the atom is empty space surrounding a tiny nucleus.

The salient features of this model are as follows: (i) The atom contains a central part called nucleus which is surrounded by electrons. (ii) The nucleus of an atom is positively charged. (iii) The size of the nucleus is very small as compared to the atomic size.

The main problem with Rutherford’s model was that he couldn’t explain why negatively charged electrons remain in orbit when they should instantly fall into the positively charged nucleus. This problem would be solved by Niels Bohr in 1913 (discussed in Chapter 10).

From the location and number of α-particles reaching the screen, Rutherford concluded the following: i) Almost 99% of the α-particles pass through the gold foil without any deflection. So atom must be having a lot of empty space in it. ii) Several α-particles get deflected at angles.

The gold foil experiment led to the conclusion that each atom in the foil was composed mostly of empty space because most alpha particles directed at the foil 1) An atom is mostly empty space with a dense, positively charged nucleus.

Most of the alpha particles did pass straight through the foil. The atom being mostly empty space. A small number of alpha particles were deflected by large angles (> 4°) as they passed through the foil. There is a concentration of positive charge in the atom.

Rutherford used gold for his scattering experiment because gold is the most malleable metal and he wanted the thinnest layer as possible. The gold sheet used was around 1000 atoms thick. Therefore, Rutherford selected a Gold foil in his alpha scatttering experiment.

These experiments led Rutherford to describe the atom as containing mostly empty space, with a very small, dense, positively charged nucleus at the center, which contained most of the mass of the atom, with the electrons orbiting the nucleus.

The atom was believed to consist of a positive material “pudding” with negative “plums” distributed throughout. Rutherford directed beams of alpha particles (which are the nuclei of helium atoms and hence positively charged) at thin gold foil to test this model and noted how the alpha particles scattered from the foil.

An Alpha Particle, Initially Very Far From The Gold Nucleus, Is Fired At 1.9 107 M/s Directly Toward The Nucleus, As In The Figure Below.

” Only a few particles bounced back because the nucleus is so small / atom is mostly empty space that few collided with a nucleus . If they bounced back it was because of alpha particle and nucleus are positive : repulsion if they bounced back it was because nucleus is massive / dense so alpha particles rebound . “