Comparison of Atomic Theories & Models “Who?” Scientist(s) “What?” Contribution to Atomic Theory “How?” Experimental and Logic Evidence to Support Contribution Atom Model (See Reverse for Image) Dalton • 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 whole- number ratios to form compounds • Chemical reactions rearrange atoms Law of Definite Proportions Law of Conservation of Mass Law of Multiple Proportions Infinitesimally small speck with no internal structure. Thompson Electrons… • have mass • have mass that is really small • are negatively charged • are a part of every atom 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. Rutherford (and others) Atoms are mostly empty space. Atoms have very dense centers and will contain most of atom’s mass. 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 Gold Foil • Most alpha particles went through foil • Some particles bounced back • Electrons are negative and small, dense part must be positive 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 Dense center called nucleus where the positive protons are kept. Electrons are spread around it. Bohr 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. Quantum Mechanics Currently accepted model of the atom. Electrons in orbitals around the n ucleus. Probability fields where th ey 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.

Atomic Model Comparison Sheet

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Comparison of Atomic Theories & Models“Who?”

Scientist(s)“What?”

Contribution to Atomic Theory

“How?”Experimental and Logic Evidence to Support

Contribution

Atom Model (See Reverse forImage)

Dalton

• 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 whole-

number ratios to form compounds• Chemical reactions rearrange atoms

Law of Definite Proportions

Law of Conservation of Mass

Law of Multiple Proportions

Infinitesimally small speck with nointernal structure.

Thompson

Electrons…• have mass• have mass that is really small• are negatively charged• are a part of every atom

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 positivestuff holding together the smallelectrons.

Rutherford(and others)

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

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

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

positive

Neutron Logic:• Mass of atoms are greater than mass of protons and

electrons. Must be another particle with neutralcharge.

• Protons stay together and make a dense nucleus

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

Bohr

Spectroscopy studies showed that the electrons couldonly be in discrete orbits around the nucleus and that theycould 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 andneutrons were with electrons orbitingaround in a circular motion like

planets around the sun.

QuantumMechanics

Currently accepted model of the atom. Electrons inorbitals around the nucleus. Probability fields where theyreside 90% of the time.

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

Nucleus has protons & neutrons butelectrons exhibit wave like propertiesand do not circle the nucleus likeBohr thought.