P1:Matter Flashcards
(27 cards)
What did the early atomic model look like before Thomson?
Dalton’s mode-atoms were thought to be tiny, indivisible spheres
Who proposed the “plum pudding” model and when?
J.J. Thomson, in 1897
What did the plum pudding model suggest about the atom?
The atom was a sphere of positive charge with negatively charged electrons embedded in it, like plums in a pudding.
What discovery led to the plum pudding model?
J.J. Thomsons discovery of electrons
What experiment challenged the plum pudding model?
The alpha particle scattering experiment by Geiger and Marsden under Rutherford’s direction.
What happen in the Rutherford’s model and the Geiger-Marsden experiment?
Most alpha particles passed through the gold foil, but some were deflected and a few bounced back.
FWhat did Rutherford conclude from the scattering experiment?
Atoms have a small, dense, positively charged nucleus where most of the mass is concentrated.
How did Rutherford’s model differ from Thomson’s?
-From the plum pudding model, the expected the particles to pass straight through the gold sheet or only slightly deflected.
-But although most of the particles did go straight through the sheet some where deflected more than they had expected and a few delflected back the way thy had come.
What problem did Rutherford’s model have?
It couldn’t explain why electrons didn’t spiral into the nucleus due to attraction
Who improved Rutherford’s model and how?
Bohr proposed that electrons exist in fixed energy levels (shells) around the nucleus, rather than moving randomly.
Why was Bohr’s model accepted?
Bohr’s model identified more clearly where electrons could be found
How has the atomic model changed over time?
The model changed from Dalton’s solid sphere, to Thomson’s plum pudding model, to Rutherford’s nuclear model, and finally to Bohr’s model with electrons in fixed energy levels (shells) around the nucleus, rather than moving randomly.
How is an atom structured in terms of charge ?
-An atom consists of a positively charged nucleus at its center.
-The nucleus contains protons and neutrons, which account for almost all of the atom’s mass.
-The electrons are negatively charged and orbit the nucleus at relatively large distances.
What is the diameter of an atom?
Approximately 1 × 10⁻¹⁰ m
What is the definition of density?
Density is the mass per unit volume of a substance.
Why do solids, liquids, and gases have different densities?
-Solids: Particles are closely packed — high density.
-Liquids: Particles are close but can move — medium density.
-Gases: Particles are far apart — low density.
What is the equation for density?
Density = mass / volume
What is the average density of an object?
It determines whether it floats or sinks .
What happens to mass when a substance changes state?
It remains the same
What effect does heating have on a system?
-Increases the internal energy of the system.
-Can raise temperature or cause a change of state.
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1 kg of a substance by 1°C.
What is specific latent heat?
The amount of energy required to change the state of 1 kilogram of a substance without changing its temperature
How is specific latent heat different from specific heat capacity?
Specific Heat Capacity: Energy to change temperature.
Specific Latent Heat: Energy to change state, without temperature change.
How do you calculate the change in internal energy due to temperature change? (specific heat capacity)
Energychange=mass×SHC×temperaturechange(Q=mcΔT)
