Unit 3: Chemistry. Development of the Atomic Theory. The History of the Atom
Unit 3: Chemistry. Development of the Atomic Theory. Atom: smallest particle into which an element can be divided and still be the same substance. Often called the “building block of matter” Theory: a unifying explanation for a broad range of hypotheses and observations that have been supported by testing
Unit 3: Chemistry. Development of the Atomic Theory. Ancient Greek philosopher He proposed that all atoms are small, hard particles that are “uncuttable” and always moving Formed into different shapes and sizes. Form different materials by joining together. Word “atom” comes from the word indivisible Democritus 440 BC
Disagreed with Democritus Unit 3: Chemistry. Development of the Atomic Theory. Aristotle 384-322 BC Greek philosopher Disagreed with Democritus
Atoms join in set ratios with other atoms to make new substances. Unit 3: Chemistry. Development of the Atomic Theory. His theory stated… All substances are made of atoms, which cannot be created, divided, or destroyed. Atoms of the same element are exactly alike and atoms of different elements are different. Atoms join in set ratios with other atoms to make new substances. John Dalton 1803
Unit 3: Chemistry. Development of the Atomic Theory. Conducted Cathode Ray experiment Known for the “plum-pudding model” There are small, negatively charged particles called electrons scattered throughout positively charge material inside the atom. J.J. Thomson 1897 Model: is a representation of an object or system
Unit 3: Chemistry. Development of the Atomic Theory. J.J. Thomson 1897 Cathode Ray Experiment Electron: negatively charged particles found in all atoms
Unit 3: Chemistry. Development of the Atomic Theory. Thomson’s student from New Zealand Conducted the gold foil experiment where positively charged particles were aimed at foil. Atom has a small, dense, positively charged nucleus. Most of an atom’s mass is in the nucleus Ernest Rutherford 1911
Unit 3: Chemistry. Development of the Atomic Theory. Niels Bohr 1913 Danish scientist living the early 1900’s Electrons travel around the nucleus in definite paths. Electrons jump from a path in one level to a path in another level.
Unit 3: Chemistry. Development of the Atomic Theory. Schrodinger and Heisenberg 1913 Current Model Twentieth century scientists There are regions inside the atom where electrons are likely to be found called electron clouds. Electron paths cannot be predicted.