Download Theories and Structure of the Atom

Theories and Structure of the Atom
Dalton’s Atom (1805)

Dalton’s model of the atom was an indivisible sphere of matter.
Dalton’s Contributions:
 Conservation of Mass (In any reaction, mass before and after the reaction will be the same)
 Elements can combine in different proportions (Ex: H2O and H2)
Thompson’s Atomic Model (1897)
Thompson’s Contributions:
 J.J. Thompson discovered the idea of charge in an atom
 His models placed the electrons throughout the positively charged atom
 AKA raisin bun model
Rutherford’s Atomic Model (1911)
Rutherford conducted an experiment where positively charged alpha particles were fired at gold foil.
His observations included:
 Most alpha particles passed straight through the foil
 A few alpha particles bounced back
Rutherford’s Contributions to the atomic model
Since most of the alpha particles passed through the foil:
1. Most of the atom is empty space
Since some of the alpha particles bounced back:
2. Part of the atom is very dense and positive. (He called this the nucleus)
Rutherford’s Atomic Model (1911)
 The nucleus is a dense mass of protons and neutrons.
 Electrons exist outside the nucleus.
Bohr’s Atomic Model (1913)
Bohr’s Contributions:
 Discovered that electrons exist in electron levels.
 Using hydrogen gas, he was able to show how electrons have a certain amount of energy and
can “jump” from one level to the next.
Subatomic Particles
Particles
Charge
Mass (amu)
Protons
1
Neutrons
1
Electrons
Negligible
(1/2000)
Location