The Atomic Structure of Atoms 

Democritus: Hypothesizing the Atom Around 460 B.C., Democritus first developed the idea of atoms as the smallest possible bit of matter. The word “atom” came from the Greek word atomos meaning indivisible Greek philosophers laid the ground work for the modern atomic theory

Dalton: The Atomic Theory John Dalton, in the early 1800’s, developed the “atomic theory” from observations gathered from many experiments. Fun Fact: Dalton was a school teacher and chemist!

Dalton’s Atomic Theory: 1. All elements are composed of atoms. Atoms cannot be divided or destroyed. (Now we know atoms can be divided) 2. Atoms of the same element are exactly alike. Atoms of different elements are different. (Now we know that atoms of the same element that are not exactly alike are called isotopes – they have a diff. # of neutrons) 3. The atoms of two or more elements can join together to form compounds.

J.J. Thomson: 1856-1940 Discovered the electron. He was awarded with the Nobel Prize in Physics in 1906.     

Lord Ernest Rutherford: 1871-1937 Ernest Rutherford was once a student of JJ Thomson Discovered that most of the atom is made up of "empty space” where the electrons move He discovered and named both the nucleus  and protons

James Chadwick: 1891-1974 James Chadwick was a student of Rutherford Discovered the neutron He found neutrons to have essentially the same mass as protons He was awarded the Nobel Prize in physics in 1935

Niels Bohr: early 1900’s Discovered electrons traveled in energy levels around the nucleus.  The lowest energy level is closest to the nucleus and holds up to 2 electrons. Higher energy levels are father from the nucleus and can contain more electrons

REVIEW: Early Atomic Chemists Democritus Named the atom Dalton Atomic Theory Thomson Discovered electron Rutherford Named the nucleus, proton, and described the “empty space” where electrons travel Chadwick Discovered neutron Bohr Discovered electron energy levels

Parts of an Atom Locations Subatomic Particles Nucleus Electron Cloud Protons Neutrons Electrons

Nucleus Is the positively charged, central part of an atom. Contains protons and neutrons. Contains almost ALL of the atom’s mass

Inside the Nucleus Protons are positively (+) charged particles Neutrons are uncharged particles (Ø) “neutrons are neutral”

Outside the Nucleus Electrons are negatively (-) charged particles located in the electron cloud. The electron cloud is arranged in energy levels and travels around the atom’s nucleus.

Neutral Atoms An atom has an overall neutral charge when: the # of electrons (-) = the # of protons (+) Remember, neutrons are neutral!

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