A Brief History of Atomic Structure and Discoveries of Key Figures, Slides of Biology

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The History of Atomic

Structure

Democritus

Named the atomfrom the Greekword “atomos”meaning indivisible.  Wrote that atomswere the smallestunit of matter tokeep its identity.

J. J. Thomson

Discovered theelectron whilerunning electricitythrough a gas.  Discovered thatelectrons werenegative.  “Plum pudding”model of the atom.

Marie & Pierre

Curie

Provided evidencefor the existence ofprotons andneutrons.  Discovered radiumand polonium.  Marie Curie was thefirst female winnerof the Nobel prizeand the first doublewinner.

Niels Bohr

Developed the“solar system”model of the atom.  The nucleus in thecenter of the atomis made of protons(+) and neutrons.  Electrons (-) orbitthe nucleus like theplanets around thesun.

Electron

Cloud Model

The current modelof the atom.  Electrons do notorbit the nucleus inorderly paths.  Electrons movearound the nucleusat near the speedof light in a generalarea.  Research continues.

Protons

Found in thenucleus of theatom.  Have a charge of +  Have a mass of 1atomic mass unit(amu)

Neutrons

Found in thenucleus of theatom.  Mass of 1 amu  Neutrons have nocharge.

What makes one element different

from another?

 The number of protonsis always the same asthe atomic number.  The number ofelectrons is usually thesame as the atomicnumber.  To find the number ofneutrons: take theatomic mass, roundedto the nearest wholenumber, and subtractthe atomic number.

Finding the number of neutrons

The mass number of this isotope oflithium is 7. Notice that 7 is equal to the totalnumber of protonsand neutrons. If you remove the protons (atomicnumber), theneutrons are left.