History of Atoms: Philosophers

History of Atoms

Early Greek Philosophers

• Empedocles believed that the four elements(Earth, Air, Fire, Water) were eternal and unchanging.
• Love mixes and combines, while strife separates and breaks apart.
• All things in the world are formed by different combinations and proportions of the four elements.
• Leucippus and Democritus thought all matter were composed of indivisible and indestructible units called uncuttable.
• Leucippus and Democritus suggested that atoms differ in size, shape, and arrangement.
• Leucippus and Democritus believed that atoms are in constant motion, colliding and interacting with each other.
• Leucippus and Democritus described void as empty space that allows atoms to move and interact.
• Aristotle thought that earth was cold and dry, water was cold and wet, air was hot and wet, fire was hot and dry.
• Aristotle believed that matter is continuous and infinitely divisible, rejecting the idea of atoms.
• Aristotle thought Elements could be transformed into one another by changing their qualities

The Fundamental Laws

• The Law of Conservation of Mass describes how the total mass of substance does not change during a chemical reaction.
• Matter cannot be created nor destroyed.
• The number of substance may change in form, but the total mass remains the same.
• The Law of Definite Proportion describes how a particular compound always contains the same element in the same proportions by mass, no matter what its source.
• Water is always 11.2% Hydrogen and 88.8% Oxygen.
• The Law of Multiple Proportion states that if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.
• Atoms of compounds are in ratio as whole number.
• In Carbon Monoxide (CO) 12g of carbon combines with 16g of oxygen.
• In Carbon Dioxide (CO2) 12g of carbon combines with 32g of oxygen.
• The mass of oxygen in CO2 (32 g) is exactly twice the mass of oxygen in CO (16 g) when combined with the same mass of carbon (12g).
• The ratio of oxygen in these two compounds is 16:32, which simplifies to a small whole number ratio of 1:2.
• In Water (H2O) 2g of hydrogen combine with 16g of oxygen.
• In Hydrogen Peroxide (H2O2) 2g of hydrogen combine with 32g of oxygen.
• The ratio of oxygen in these two compounds is 16:32, which simplifies to a simple whole number ratio of 1:2.

History of Atoms

• John Dalton's Atomic Theory outlines how all matter is composed of extremely small particles called atoms.
• Atoms of a given element are identical in size, mass, and other properties.
• Atoms cannot be subdivided, created, or destroyed.
• Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
• In chemical reactions, atoms are combined, separated, or rearranged.
• Joseph John Thomson proposed the "Plum Pudding" Model of the atom in 1897.
• Thomson's Cathode Ray Tube Experiment contributed to the discovery of electrons.
• Ernest Rutherford's Nuclear Model describes how the atom is the basic building block of matter.
• An atom has a tiny, dense, positively charged core called the nucleus.
• Electrons orbit the nucleus at a distance.
• Electrons are much smaller and lighter than the nucleus and occupy the vast majority of the atom's volume.
• The atom is mostly empty space.
• Neil Bohr's Planetary Model explains that light is absorbed when an electron jumps to a higher energy orbit and emitted when an electron falls into a lower energy orbit.
• Erwin Schrödinger's Quantum Mechanical Model describes wave particle nature of atom and Heisenberg's uncertainty principle.
• It also describes electron Orbital.
• James Chadwick discovered neutrons. These have symbol n, zero charge and Atomic Mass Unit 1.00865.
• Electrons have symbol e-, negative charge and Atomic Mass Unit 5.486 x 10-4.
• Protons have symbol p, positive charge and Atomic Mass Unit 1.007276.