History of Atomic Theory Flashcards
What is the first theory of the atomic model proposed by ancient Greeks?
Matter cannot be divided forever: that there is a tiniest unit that can’t be divided anymore.
This theory emphasizes the indivisibility of matter.
What were the four elements believed to make up all matter according to ancient Greek theories?
- Earth
- Water
- Air
- Fire
This concept was widely accepted before modern atomic theory emerged.
Who proposed a modern atomic model based on experiments in the early 1800s?
John Dalton
Dalton’s model marked a significant shift from philosophical reasoning to empirical evidence.
What did Dalton say about atoms?
- Atoms are small
- Indestructible
- Indivisible particles
- All matter is made up of atoms
Dalton compared atoms to billiard balls to illustrate their indivisible nature.
What significant addition to the atomic model did J.J. Thomson make in 1900?
The negatively charged electron
Thomson’s discovery of the electron altered the perception of atomic structure.
What model did J.J. Thomson propose?
Plum Pudding Model
This model suggested that electrons were distributed within a positively charged ‘soup’.
What major discovery did Ernest Rutherford make in 1910?
Atoms are mostly empty space, and the nucleus is positive.
Rutherford’s gold foil experiment revealed the nuclear structure of the atom.
What did Rutherford’s experiment with alpha particles demonstrate?
- Most particles passed through the gold foil
- Some particles were deflected or bounced back
This indicated the presence of a dense, positively charged nucleus.
What model did Niels Bohr propose in 1913?
Electrons orbit the nucleus in energy shells.
Bohr’s model introduced the concept of quantized energy levels for electrons.
What did James Chadwick discover in 1932?
The existence of neutrons.
Chadwick’s discovery completed the understanding of atomic structure by identifying the neutron.
Fill in the blank: Dalton’s atomic theory states that all matter is made up of _______.
[atoms]
True or False: The Plum Pudding Model suggested that electrons are located in a positively charged matrix.
True
What did Rutherford conclude about the nucleus of an atom?
The nucleus is positive and holds most of an atom’s mass.
This conclusion was pivotal in the development of modern atomic theory.
