LT#1: Atomic Structure Flashcards
How did Dalton prove that atoms exist?
He noticed the amounts of gases reacted in various whole number ratios.
Therefore must be different building blocks with definite and characteristic weights.
How does Dalton’s model describe atoms?
Small indestructible spheres called atoms and stated:
- All matter is made of atoms.
- Atoms of the same element have the same average mass, size and unique properties.
- Atoms cannot be converted into atoms of another element through chemical reactions.
- Atoms of different elements combine in specific proportions to form compounds.
How did Thompson prove that electrons exist and that they are negative?
Experimented with cathode ray tubes which create beams of small particles. He placed charged plates on either side of the beam to determine its charge.
Observed that the beams are deflected towards positively charged plates. The beam must contain negative particles because opposite charges attract.
Since atoms are neutral, they must contain negative particles that can be removed from a positive material.
Describe Thompson’s model
Atoms are positively charged spheres with embedded negative electrons (Plum Pudding Model).
How did Rutherford prove the nucleus exists and that it is positive?
Shot positively charged alpha particles from radioactive elements at a thin piece of gold foil.
Observed that most particles went straight through. Some deflected at large angles back towards the particle gun.
Since most alpha particles went straight through, atoms are made of mainly empty space. The ones that deflected back must have hit a dense positive structure because they were repelled off.
Describe Rutherford’s model
Atoms have a small dense positive nucleus with electrons travelling around it (planetary model). He concluded that the nucleus was made of individual particles (which he called protons) equal in charge to that of a negative electron.
Describe the inferences Bohr made based on Rutherford’s model
Because of opposite charge attraction, electrons should quickly spiral into the nucleus causing a nuclear explosion.
Since this is not often observed, electrons must behave differently than macroscopic objects because they are so small.
What scientific ideas did Bohr apply when describing the structure of atoms?
Applied the ideas of Max Plank (energy is only transferred in specific amounts) and Albert Einstein (light is packets of energy called photons) to mathematically predict where electrons are.
Also wanted to explain atomic emission spectra (atoms give off a unique colour pattern when heated).
What was Bohr able to predict mathematically?
Bohr was very successful at mathematically predicting the amounts of energy that electrons actually travel at around the nucleus.
His model also accurately predicts the colours of light that are given off when electrons change orbits, but only for atoms that have 1 electron.
How does Bohr describe how electrons travel around the nucleus?
- Electrons are only found in specific allowable energy levels that represent fixed, circular orbits around the nucleus.
- While in an orbit, electrons do not gain or lose energy.
- An electron changes orbits by emitting or absorbing a specific quantity of energy that is exactly equal to the difference in energy between the 2 orbits. See diagram below.
How did Rutherford prove the existence and charge of neutrons
He calculated the mass of protons that it would take to balance the negative charge of electrons in an atom.
He noticed actual atoms weighed significantly more than his calculations.
There must be another particle in the nucleus to account for the missing mass. These also must be neutral in charge so that they don’t upset the charge balance in atoms.
Describe the Bohr-Rutherford model
The nucleus of an atom contains protons and neutrons. Electrons travel around the nucleus in fixed circular orbits based on the amount of energy they possess.
What is Heisenberg’s Uncertainty Principle?
It is impossible to measure the position and the momentum of an object at the same time. The more accurately one property is measured the less accurate the other property can be determined.
How does the Uncertainty Principle disprove Bohr’s model?
Bohr’s model is incorrect because it assigns specific fixed paths (circular obits) and definite speeds (energy levels) simultaneously.
Describe how de Broglie’s work disproves Bohr’s model?
He describes all matter including electrons as waves. The wavelength of an electron moving at Bohr’s first energy level is too large to fit into the orbit Bohr described
