The Development of Atomic Theory

10.1 The Nature of Matter Matter is a term used to describe anything that has mass and takes up space. Greek philosophers Democritus and Leucippus proposed that matter is made of tiny particles called atoms. Atoms were an idea that few believed. The first evidence was called Brownian motion for Robert Brown, who first noticed the jerky motion of tiny particles.(1827)

Atom from the Greek word atomos that means indivisible Democritus Atom from the Greek word atomos that means indivisible

Democritus Proposed that all atoms are small hard particles made of a single material Different shapes and sizes Atoms are always moving They form different materials by joining together

John Dalton(1803) All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike (1803) The solid sphere model - like a sour ball

An early model In 1897 English physicist J. J. Thomson discovered that electricity passing through a gas caused the gas to give off particles that were too small to be atoms. These negative particles were eventually called “electrons.”

Plum –Pudding Model-Chocolate Chip Cookie Model The atom is mostly positively charged material. Electrons are small, negatively charged particles located throughout the positive material. Proved atoms can be divided into smaller parts

Ernest Rutherford Designed an experiment to test Thomson’s theory. Proposed that in the center of the atom is a tiny dense positively charged region called the nucleus. Tootsie roll pop

Rutherford’s Gold Foil Experiment He aimed a beam of small positively charged particles at a sheet of gold foil.The particles were larger than protons.

The nuclear model In 1911, Ernest Rutherford, Hans Geiger, and Ernest Marsden did a clever experiment to test Thomson’s model. We now know that every atom has a tiny nucleus, which contains more than 99% of the atom’s mass.

Bohr’s Model of the Atom Electrons travel in definite paths around the nucleus. These paths are located in levels at certain distances from the nucleus Gob stopper model

Bohr Model A Planetary Model of the Atom                                                                                 

Erwin Schrodinger and Werner Heisenberg Ferrero Rocher Model They explained the nature of electrons in an atom

Electrons and the Periodic Table Order of filling levels

Energy levels These levels are divided into smaller regions called orbitals. These regions are designated by the following letters s,p,d and f

Orbitals s- can hold 2 electrons p- can hold 6 electrons d- can hold 10 electrons f- can hold 14 electrons

Orbitals The Atomic Orbitals Atom in a Box Real-Time Visualization of the Quantum Mechanical Atomic Orbitals The orbital images on this page represent the shape of the atomic orbitals. The clouds you see are the probability distribution of an electron bound to a Hydrogen nucleus.                                               

The Modern Atomic Theory Electrons do not travel in definite paths as Bohr had suggested The exact path of a moving electron cannot be predicted. Electron clouds are regions inside the atom where electrons are likely to be found

10.1 Atoms A single atom is the smallest particle that retains the chemical identity of the element.

10.1 Molecules A molecule is a group of two or more atoms joined together chemically.