Unit 2 - Atomic Concepts - History of the Atom Flashcards
What did Aristotle state in 384 BC? (2)
- Matter is composed of 4 elements
- Matter is continuous, not atomistic
What term Leucippus and Democritus create in 450 BC?
Atomos
What did Leucippus and Democritus picture atoms as?
Pictured atoms as round and smooth
Definition of Atomos
- Point at which
- Matter can no longer be subdivided
What did Lavoisier state in the early 1700s?
Substances can be made up of 2 or more elements
Fun Fact: Lavoisier stated that matter cannot be created or destroyed
Law of Definite Proportions
Compound - Same unique elements are in definite proportions
Law of Multiple Proportions (2)
- Elements can join in different ways
- Each way creates a unique substance with its own properties
What is Dalton’s Theory? (4)
- All matter is composed of atoms
- All atoms in an element are the same and different from atoms in another element
- Compounds - Combined atoms of unique elements in fixed proportions
- Chemical reaction = rearrangement of atoms
What did they find out in the 20th century about the “Indivisible Atom”?
Made up of subatomic particles
What did JJ Thomson determine in 1897? (7)
- Discovered that electron
- Used the Cathode Ray Tube
- Electrons have a high charge - mass ratio
- Atoms are divisible
- Protons = Electrons
- Since matter is neutral
- Positive charges is evenly spread out, and negative charges are in bits
Plum Pudding Model?
Imagine a big, soft, spongy dessert like a plum pudding (or, in modern terms, a chocolate chip cookie). In this model, the pudding or cookie dough represents the positive charge, which is spread evenly throughout the atom. The chocolate chips (or plums) are the electrons, which are negatively charged particles scattered throughout this positive charge. The electrons are the “bits” within the atom.
This was Thomson’s idea of how the atom was structured before the discovery of the nucleus, which later models revealed was not quite right.
What did Rutherford discover? (5)
- Used the Gold Foil Experiment
- Discovered the atom’s nucleus
- Atom’s mass is concentrated in small + charges
- Electron is the farthest away from atom
- Atoms are mostly empty space
What was Bohr’s contribution to chemistry? (4)
- Created the Planetary Model
- Electrons revolve around nucleus
- In Circular Orbits
- In Shells
Definition of Orbitals (3)
- 3D Space Outside Nucleus
- Found in Shells
- Orbitals are where electrons have a high probability being found
What is the Wave Mechanical Model (4)
- Replaced Bohr Model
- Also known as the Electron Cloud Model
- Electrons found in 3D Orbitals
- Each energy level contains one or more orbitals