Atomic Theory Flashcards
What was Democritus’ theory?
- Matter can be broken down to particles, but particles can’t be broken down.
- Particles are called atomos.
What was Democritus’ experiment?
Split rock into half and saw it had same properties.
What was Democritus’ model of the atom?
Solid Sphere
What was Aristotle’s theory?
All matter was made of the following elements: Earth Air Fire Water
What was Franklin’s theory?
Electricity was composed of negatively charged particles.
Atoms usually have a _______ charge
Neutral
Where does the word electricity come from?
Elektron meant amber in Greek.
What was Dalton’s theory?
- Matter is composed of small particles called atoms.
- Atoms of a given element are the same size and shape, but differ from other atoms of different elements(FALSE, exception are isotopes).
- Atoms can’t be subdivided, created, nor destroyed(False, due to nuclear reactions).
- Atoms can combine to form compounds with whole number ratios(Law of Multiple Proportions). Compounds combine in whole number ratios.
- In chemical reactions atoms are combined, seperated, or rearranged.
What was Dalton’s model of the atom?
Solid Sphere that was indivisible
What did Dalton accept to make his five statements?
- Two elemets can combine to form a compound.
2. Pure substances of a compound have the same composition by mass.
What was JJ Thomson’s theory?
- If atoms are neutral, they must be positivily charged particle in the atom.
- If atoms have mass, there should be other particles with a greater mass.
- There is a particle in atom that is negativly charged.
- This particle has mass.
What was Thomson’s model of the atom?
Known as the Plum pudding Atom.
Majority/Center is positive, while electrons are on the outside scattered.
What was the significance of Thomson’s theory?
First discovery of a sub-atomic particle (electrons).
Who confirmed Thomson’s theory?
Robert Millikan, did the oil drop experiment, which showed how tiny the electron was compared to the whole atom.
What was JJ Thomson’s experiment?
Conducted two significant experiments.
Used a Cathode Ray Tube, Alpha Particles, Magnet, and Paddlewheel.
In the first experiment shot the electrons(later named electrons) straight, but after it hit the magnet, curved towards positive side, indicating the particle had a negative charge.
In second experiment shot electrons straight, and turned the paddlewheel indicating the particles had mass.
What was Rutherford’s theory?
- Most of the atom was empty space.
- The nucleus is small, dense, and positive.
- Proposed electrons moved around the nucleus like the planets do to the sun, which was later disproved.
What was Rutherford’s experiment?
Shot positive alpha particles towards gold foil, by using lead with a hole in it to direct the alpha particles.
Noticed that most of the alpha particles went through the gold foil, but some deflected at different angles, which indicated that most of the atom was empty space, and when the alpha particle did deflect it hit the nucleus.
What was Chadwick’s theory?
- Credited witht he discovery of the neutron.
What was Chadwick’s experiment?
Bombared Be with alpha particles which emitted an energetic stream of radiation.
What was Rutherford’s model of the atom?
Nucleus is in the center(proton), while the electrons orbit in a definite ring.
Why did it take so long to discover the neutron?
- Neutron has no charge.
2. Great Depression
What was Bohr’s theory?
- Placed each electron at a specfic energy level.
- Electrons moved in defintie orbits around the nucleus.
- The energy levels are located at a specific distance from the nucleus.
- Electrons are located in energy levels outside of the nucleus.
- There is no change in energy when electron is in an energy level.
- Ground State is when th electron(s) is at it’s lowest possible energy state (when e- is stable).
- Delta E (Change in Energy) occurs ehen the electron changes energy levels.
- Electron’s absorb energy to move to a higher energy level, and release/emmit energy to move to a lower energy level.
What was Bohr’s model of the atom?
- Placed each electron at a specfic energy level.
- Lowest energy level is closest to nucleus.
- Electrons can move between energy levels.
- Electrons will never be found in between energy levels..
- Electrons are attracted to the positive nucleus but remain in orbits that revolve around the center nucleus.
- The orbit shells are called Principle Energy Levels (PEL’s), and are the regions where an electron can be found outside of the nucleus.
Who created the Wave-Mechanical Model?
Erwin Schrodinger
What is another name for the Wave-Mechanical Model?
Electron Cloud
What does the Wave-Mechanical Model state?
- Propesed that paricles have a dual-wave particle nature
- Electrons don’t travel in perfect orbits around the nucleus due to quantum mechanics.
- Electrons exist in a 3-D region around the nucleus.
- The probable location of the electron is called an orbital.
- Impossible to determine the exact location of an electron.
- The probable location depends on how much energy the electron has.
List in chronological order, all significant people or theories whom contributed to atomic theory.
- Democritus
- Aristotle
- Franklin
- Dalton
- Thomson
- Rutherford
- Bohr
- Wave-Mechanical Model
- Chadwick
Ground State vs Excited State
- In excited state the average distance between the nucleus and electron increases.
- Ground State is when th electron(s) is at it’s lowest possible energy state (when e- is stable).
- Excited State occurs when energy is absorbed by the electron, which makes it move up in energy levels.
- Atomic Excitation is when the electron absorbs energy, while Atomic De-xcitation is when the electron releases/emitts energy.
- Electron only absorbs require amount of energy, no more, no less.
Proton
Neutron
Electron
Proton - p, 1 amu, +1
Neutron - n, 1 amu, 0
Electron - B- or e-, 1/1826 amu, -1
Units of measurement
amu - Atomic Mass Unit(Dalton)
1 amu - 1/12 mass of C-12
1 C atom - 12 amu
What is atomic number?
Number of protons
Number of protons = __________
Why?
Number of electrons because usually atoms are neutral(exception are ions).