Unit 2: Atomic Theory and Structure

Question 1

What is the smallest unit of matter?

Answer 1

An atom

Question 2

What three parts are atoms made up of?

Answer 2

Protons (+), Neutrons (neutral), and Electrons (-)

Question 3

Where are the protons and neutrons located?

Answer 3

The center (the nucleus).

Question 4

Where are the electrons located?

Answer 4

Outside of the nucleus in the electron cloud.

Question 5

Democritus (465 / 400 BC)

Answer 5

• First to believe in the idea of atoms
• Not based on scientific method
  His theory:
  
  • The universe is consisted of atoms and the void that they exist in
  • Atoms are very tiny
  • Atoms cannot be destroyed, and are different sizes, temperatures and shapes
  • There are an infinite number of atoms and all are always moving
    Model: Simple sphere

Question 6

John Dalton (1803)

Answer 6

5 part atomic theory:
- All elements are made of atoms
- Atoms of an element are identical
- Atoms of different elements are different
- Atoms combine in simple whole number ratios to make compounds
- Atoms may rearrange in chemical reactions but are not changed in the reaction
Model: Simple sphere

Question 7

JJ Thomson (1897)

Answer 7

• Used gas discharge tube to discover electrons
• Used rays and electric fields to find mass-to-charge ratio which is how he discovered the electrons
  Model: electrons floating in an atom with a negative charge, the space/void in the atom has a positive charge (Plum Pudding Model)

Question 8

Robert Millikan (1909)

Answer 8

• Found the unit charge of an electron
• Used the oil drop test to come to this conclusion
  Models: No new contributions

Question 9

Ernest Rutherford (1911)

Answer 9

• Fired alpha particles (basically just nuclei) at a very thin gold foil made of just a few atoms and when they passed through learned that atoms have a nucleus
  Model: a sphere representing the nucleus with smaller spheres orbiting the center

Question 10

Niels Bohr (1922)

Answer 10

• Used light to discover that different atoms have different amounts of energy
• Different number of electrons in each orbit
  Model: A proton as the nucleus with electrons revolving around it, each orbit has a certain amount of energy.

Question 11

Quantum Mechanical Model

Answer 11

A mathematical model that predicts the electron locations and paths within an electron cloud.
Resulted from de Broglie, Schrödinger, and Heisenberg.
Their studies proposed electrons acting as particles or waves, which is how this model originated.

Question 12

Electron Cloud

Answer 12

places where electrons are likely to be found

Question 13

Heisenberg uncertainty principle

Answer 13

It is impossible to know both the momentum and the position of a particle at the same time

Question 14

James Chadwick (1932)

Answer 14

• the atomic mass of most elements is double the number of protons
• discovered neutrons in 1932