History of Atomic Theory (Lesson 3) Flashcards
What did the Greek call an atom?
A tomos - meaning indivisible
Order of Atomic History
Dalton Thompson Rutherford Bohr Quantum
Dalton’s Atomic Theory
- First complete attempt to describe all matter in terms of atoms and their properties
- Based his theory on the law of conservation of mass and law of constant composition
- All matter is made of atoms (which are indivisible)
- All atoms of a given element are identical in mass and properties
- Compounds are combinations of 2 or more types of atoms
- A chemical reaction is a rearrangement of atoms
Cons to Dalton’s Atomic Theory
It didn’t recognize that atoms can now be broken down further in subatomic particles
Thompson’s Atomic Model
- Plum Pudding
- First model to describe atom composition
- Discovered atoms are divisible
- Discovered electron
- He determined that the ray emitted from cathode tube weren’t rays or waves but very small and light negatively charged particles
Thompson’s Experiment/Procedure
- Demonstrated with cathode ray tubes that atoms could be broken down into smaller particles.
- Showed that negatively charged particles could be ejected from atoms, leaving them positively charged
- Therefore negative particles are embedded in a positively charged matter
- Applied High voltage to partially evacuated tube called a cathode-ray tube
- The ray (beam of electrons) T. said that atoms are neutral and have positively charged components too (they released negative entities)
- Assumed that atom = positive diffuse cloud with random pieces of electrons in it.
Rutherford’s Atomic Model
- Discovered the proton
- Described atom as a tight and dense positive core (nucleus) which almost all mass is concentrated
- This nucleus is then circled by electrons
Rutherford’s Experiment/Procedure
- Radioactive source hit a thin sheet of gold with alpha particles (+ charge, 4 atom so 2 neutrons 2 protons)
- The alpha particles should travel with few deflections
- However many alpha particles were deflected at large angles and reflected never hitting the detector
- A center of concentrated positive charge that contains most of the atoms mass was the cause for deflection
Bohr’s Atomic Model
- Stated that a Hydrogen atom electron moves around the nucleus in a specific circulatory orbit
- Introduced energy levels (electrons)
Cons to Bohr’s Atomic Model
-Quantum science discovered that electrons don’t move in circular paths
Quantum Theory
- Electrons were not particles or waves but had some properties of both and some of neither
- Introduction of an Electron Cloud
- Now atoms can be separated into protons, neutrons, and electrons
What is an electron cloud?
the area around the nucleus where the probability of finding an electron is the highest
What is the Heisenberg Uncertainty Principle?
-states that you can’t know the exact speed and position of an object
- everything on earth behaves like a particle and wave at the same time
- Electrons and atoms have big enough wavelengths that can be measured but doesn’t have a position while a particle doesn’t have a wavelength (their exact speed and position at a point in time is unknown)
What was Louis Debroglie’s contribution to the Atomic History?
- He discovered that particles can act like waves and waves can act like particles
- So electron’s can better be described as waves vs particles
- Electron energy can better be analyzed by their wave length rather than mass & velocity
What was Erwin Schrodinger’s contribution to the Atomic History?
-developed a mathematical equation to show where an electron was located around the central nucleus
(electron cloud model)
