Chapter 3 Scientist

Niels Bohr

Studied electrons and nuclei, proposed fixed circular orbits for electrons.

Where are electrons located in Bohr's model?

In fixed circular orbits around the nucleus.

What did Bohr learn about electron orbits?

Electrons orbit at specific allowed distances with quantized angular momentum.

Bohr's discovery about particles and energy levels

Each particle corresponds to a specific energy level.

James Chadwick

Discovered the neutron, studied its properties.

Where is the neutron located?

In the nucleus of an atom.

What is unique about the neutron?

It has no electrical charge and a mass similar to that of a proton.

Marie Curie

Discovered radioactivity as an atomic property; named polonium and radium.

What did Curie's research reveal about radiation strength?

It depends only on the quantity of uranium or thorium, not the chemical form.

John Dalton's First Postulate

Matter is composed of exceedingly small, indivisible particles called atoms.

Dalton's Second Postulate

All atoms of a given element are identical in mass and properties.

Dalton's Third Postulate

Atoms of different elements combine in simple, whole-number ratios to form compounds.

Dalton's Fourth Postulate

Chemical reactions involve rearrangement of atoms; they are neither created nor destroyed.

Louis de Broglie's Contribution

Studied wave-particle duality, especially for electrons.

What did de Broglie say about electron energy?

An electron's energy determines its wavelength.

Werner Heisenberg's Uncertainty Principle

It's impossible to know both the exact position and momentum of an electron simultaneously.

Dimitri Mendeleev

Organized elements into the Periodic Table based on their properties.

How did Mendeleev use atomic structure?

He predicted undiscovered elements' properties by leaving gaps in his table.

Robert Millikan

Studied the electron and measured its charge using the oil drop experiment.

What is the charge of a single electron?

Approximately $1.6 \times 10^{-19}$ coulombs.

Describe the Oil Drop Experiment setup.

Anatomizer sprayed oil into a chamber; drops fell through a hole between plates.

What did Millikan determine about the oil drops?

He measured their mass and calculated the charge of an electron.

Ernest Rutherford's Contribution

Studied protons, electrons, and alpha particles, proposed a nuclear atom structure.

What did Rutherford learn from the Gold Foil Experiment?

Most of the atom is empty space with a dense nucleus containing positive charge.

J.J. Thomson's Discovery

Discovered the electron and proposed the existence of positive ions.

What did Thomson conclude from the Cathode Ray Experiment?

Cathode rays are negatively charged electrons.

Joseph Proust's Law

Law of Definite Proportions: Elements combine in fixed ratios by mass.

What did Proust study in his experiments?

Analyzed metallic oxides, sulfides, and carbonates.

Antoine Lavoisier's Contribution

Credited with the Law of Conservation of Mass.

What does the Law of Conservation of Mass state?

Mass cannot be created or destroyed.

How did Lavoisier die?

Executed by guillotine during the French Revolution.

What element did Lavoisier discover in combustion?

Named oxygen and recognized hydrogen as an element in water.

What aspect of atoms did Curie emphasize?

Radioactivity is an atomic property.

What relation did Chadwick find between neutrons and protons?

Neutrons have a mass similar to protons.

What major atomic structure did Dalton suggest?

Atoms are indivisible and fundamental components of matter.

What did Heisenberg's discovery imply for electron behavior?

Electrons have inherent uncertainty in their position and momentum.