Evolution of the atomic model Atomic Theory Evolution of the atomic model

Objectives: Describe the historical development of atomic theory Identify modern model of the atom Objectives:

An atom of one element cannot be changed into an atom of another element All atoms of the same element are exactly alike All elements consist of atoms that cannot be divided Early 1800’s John Dalton

J.J. Thomson Created the “plum pudding” model Electrons were scattered throughout a ball of positive charge Discovered electrons – tiny negatively charged particles Created the “plum pudding” model J.J. Thomson

Ernest Rutherford Gold Foil Experiment Shot a beam of positively charged particles at a sheet of gold foil Found some were deflected at extreme angles Proved the existence of a dense positive core Ernest Rutherford

We now have …– early 1900’s Electrons – negatively charged particles outside of the nucleus Nucleus – densely packed positive charged mass at center of atom Protons – positively charged particles in the nucleus

Neils Bohr Each electron has a specific energy Electrons orbit the nucleus in fixed paths This is the model that we draw in class

Cloud Model Electrons do not orbit like planets They move rapidly in a cloud-like region Electrons at different energy levels are likely to be found in different places

Modern model of the atom At the center of the atom is the nucleus, containing protons and neutrons. 1 Surrounding the nucleus is the electron cloud 2 Most of the atom’s volume is empty space 3 Most of the atom’s mass is in the nucleus 4