Ch.4 Flashcards
List the four statements of Dalton’s atomic theory
- atoms, which are indivisible (incorrect can be divided into electrons, protons, neutrons)
- Atoms of same element are identical. Atoms in one element are different from the atoms in another element (incorrect, atoms of same element have same atomic number; Dalton didn’t know about isotopes)
- Atoms of different elements can physically mix together or chemically combine in simple whole-number ratios to form compounds.
- Chemical reactions occur when atoms are separated from each other, joined, or rearranged in a different combination.
Cathode ray Tube experiment
Passed cathode ray (electrons) through gases at low pressure from anode to cathode.
Positive disk attracted cathode ray and negative disk repelled.
Cathode Ray Tube Conclusions
all atoms contain neg charged electrons
Plum Pudding Model
- Developed by JJ Thomson in 1904.
- electrons inside of a positive charged solid sphere.
- reveals the existence of “electrons”
The Gold Foil experiment
Rutherford and his co-workers used alpha particles directed at thin piece of gold
particles should have passed + slight deflection but didnt, instead most alpha particles went straight through
what are alpha particles
two protons and two neutrons (helium atoms)
Gold Foil Experiment Conclusions
- atom is mostly empty space
Rutherford’s Nuclear Model
- Used alpha particles beam to direct to a thin gold.
- Find: lack of deflection for majority of area except a small region that concentrated in a small, positively charged region
Bohr Model of the Atom
Electrons orbits that have a set size and energy.
The energy of the orbit is related to its size.
Radiation is absorbed/emitted when an electron moves orbits.
The nucleus protons and neutrons.
Oil drop experiment
suspended negatively charged oil droplets between two charged plates, then he changed voltage on plates to see hwo this affected droplets’ rate of fall
Millikan Experiment conclusion
Uses charge to calculate electron’s mass.
who was first to suggest existnece of atoms and reason that atoms are indivisible/indestructable
greek philospher democritus
why was democritus’s ideas wrong?
didnt explain chemical behavior, lacked experimental support
who used experimental methods to transform democritus’s ideas on atoms into a scientific theory?
John Dalton
How was John Dalton able to study atoms even though he could’t observe them directly? What evidence did he use to formulate atomic theory?
observed thta when atoms mix they maintain their own identity unless they combine in a chem reaction
How was democritus’s idea of atom diff from dalton?
Democritus hypothesised that everything was made of indivisible particles but Dalton knew the number of varieties those particles came in
what instrument can be used to observe individual atoms?
scanning electron microscopes
(beam of electrons focused on sample; can move atoms around)
J. J. Thomson
discovered electrons (Cathode ray experiment)
Robert A. Millikan
find quantity of electron’s charge (oil drop experiment)
What did James Chadwick do?
confirmed existence of neutrons
What did Eugen Goldstein do?
found protons
Plum Pudding Model vs. Rutherford’s Model: diff
presence of a nucleus in Rutherford’s model, while the plum pudding model lacks a nucleus.
Rutherford’s Model vs. Bohr’s Model: diff
Bohr’s introduction of quantized energy levels for electrons, while Rutherford’s model does not include this feature.
Plum Pudding Model vs. Bohr’s Model: diff
absence of quantized energy levels in the plum pudding model
Plum Pudding Model and Rutherford’s Model: sim
acknowledge the presence of negative electron
Rutherford’s Model and Bohr’s Model: sim
existence of a central, positively charged nucleus within the atom. electrons orbiting around this nucleus.
Plum Pudding Model and Bohr’s Model: sim
electrons as negatively charged
Common to All Three Models
- has negative electrons moving in atom
- balance of positive and negative charges in atom
