Progression of Atomic Models: Dalton to Quantum Mechanical

Who is credited with the first atomic model?

Democritus (460-370 BC)

What did Democritus propose about matter?

Matter is made of tiny, solid, indivisible particles called atoms.

What are the different properties of matter according to Democritus?

They are due to differences in size, shape, and movement of atoms.

Which philosopher rejected Democritus' atomic theory?

Aristotle (384-322 BC)

What was Aristotle's view of matter?

He believed everything was composed of the four elements: earth, air, fire, and water.

What are the three basic laws uncovered by scientists during Dalton's time?

1. Law of Conservation of Mass: Matter cannot be created or destroyed. 2. Law of Definite Proportions: A chemical compound always contains the same proportions of elements by mass. 3. Law of Multiple Proportions: Elements combine in ratios of small whole numbers.

What did John Dalton formulate in the early 1800s?

The first modern atomic theory.

List the five points of Dalton's atomic theory.

1. All matter is composed of atoms. 2. All atoms of one element are identical. 3. Atoms of different elements are different. 4. Atoms combine to form compounds. 5. Atoms are indivisible.

What flaw exists in Dalton's second point about atoms?

Isotopes of an element are not identical; they differ in the number of neutrons.

What flaw exists in Dalton's fifth point about atoms?

Atoms are divisible into smaller particles (protons, neutrons, electrons) and can be broken down in nuclear reactions.

Who discovered the electron and when?

J.J. Thomson in 1887.

What is the plum pudding model?

A model where negative electrons are embedded in a uniform positively charged 'soup' of matter.

What significant discovery did Ernest Rutherford make in 1909?

He discovered the nucleus of the atom.

What was the outcome of Rutherford's Gold Foil Experiment?

Some alpha particles were deflected, indicating the presence of a dense, positively charged nucleus.

What conclusions did Rutherford draw from his Gold Foil Experiment?

1. The atom has a small, dense, positively charged nucleus. 2. Most of the atom is empty space.

Who discovered the neutron and with whom?

Ernest Rutherford discovered the neutron while working with James Chadwick.

What is the Bohr model of the atom?

A model where electrons are restricted to specific energies and follow paths called orbits around the nucleus.

What is the current model of the atom called?

The Quantum Mechanical Model.

What do we know about electron locations in the Quantum Mechanical Model?

Electrons exist in regions called orbitals, and their paths are random and cannot be predicted.

What is another name for the Quantum Mechanical Model?

The 'electron cloud' model.

Who contributed to the development of the Quantum Mechanical Model?

Scientists including de Broglie, Schrödinger, Pauli, and Heisenberg.

What is the significance of Dalton's atomic theory?

It revolutionized the understanding of matter and its smallest building block, the atom.

What did the Law of Conservation of Mass state?

Matter cannot be created or destroyed during a chemical reaction.

What does the Law of Definite Proportions state?

A chemical compound always contains the same proportions of elements by mass.

What does the Law of Multiple Proportions explain?

If two elements form multiple compounds, the ratios of the masses of the second element with a fixed mass of the first will be in small whole number ratios.

What was the main limitation of Democritus' ideas?

They could not be tested experimentally at the time.