Atomic Model Comparison Sheet

Comparison of Atomic Theories & Models “Who?” Scientist(s)

Dalton

Thompson

Rutherford (and others)

“What?” Contribution to Atomic Theory • • •

Quantum Mechanics

Atom Model (See Reverse for Image)

Atoms cannot be broken down or destroyed All atoms of an element have the same properties Atoms of different elements have different phys. and chem. properties • Atoms of diff elements combine in simple wholenumber ratios to form compounds • Chemical reactions rearrange atoms Electrons… • have mass • have mass that is really small • are negatively charged • are a part of every atom

Law of Definite Proportions

Cathode Ray Tube • Paddle wheel set in motion • Mass of cathode plates didn’t change much • Went towards positive side of magnetic field • Happened using any metal and any gas

“Plum pudding” model with positive stuff holding together the small electrons.

Atoms are mostly empty space. Atoms have very dense centers and will contain most of atom’s mass.

Gold Foil • Most alpha particles went through foil • Some particles bounced back • Electrons are negative and small, dense part must be positive

Dense center called nucleus where the positive protons are kept. Electrons are spread around it.

Protons… • are positively charged • more massive than electrons Neutrons… • neutral particles in atom center about the same mass as protons • minimize electronic repulsion of protons

Bohr

“How?” Experimental and Logic Evidence to Support Contribution

Infinitesimally small speck with no internal structure.

Law of Conservation of Mass Law of Multiple Proportions

Neutron Logic: • Mass of atoms are greater than mass of protons and electrons. Must be another particle with neutral charge. • Protons stay together and make a dense nucleus

Spectroscopy studies showed that the electrons could only be in discrete orbits around the nucleus and that they could absorb a quantum of energy to get to the next level. When they dropped down in energy they released a photon of light.

Spectroscopy studies and mathematical calculations that perfectly described the Hydrogen Atom.

Dense center where the protons and neutrons were with electrons orbiting around in a circular motion like planets around the sun.

Currently accepted model of the atom. Electrons in orbitals around the nucleus. Probability fields where they reside 90% of the time.

Dual nature of light, photoelectric effect, Einstein & Planck’s studies.

Nucleus has protons & neutrons but electrons exhibit wave like properties and do not circle the nucleus like Bohr thought.