The Particle Model (OCR GCSE Physics A (Gateway)): Flashcards
Exam code: J249
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Define plum pudding model.
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Cards in this collection (40)
Define plum pudding model.
The plum pudding model described the atom as a ball of positive charge with negatively charged electrons embedded within it.
What three observations were made when alpha particles were fired at thin gold foil in Rutherford's scattering experiment?
In Rutherford's scattering experiment:
Most alpha particles passed straight through the foil
Some alpha particles were deflected
A small number of alpha particles bounced back
True or False?
In the plum pudding model, the atom has a positively charged nucleus surrounded by orbiting electrons.
False.
The plum pudding model described the atom as electrons embedded in a ball of positive charge. A central nucleus with orbiting electrons was proposed in the later nuclear model.
Why did the results of Rutherford's alpha particle scattering experiment lead to the plum pudding model being replaced?
The plum pudding model could not explain why some alpha particles bounced back from the gold foil. This observation suggested atoms contain a small, dense, positively charged nucleus, which contradicted the uniform distribution of charge in the plum pudding model.
In Rutherford's scattering experiment, a few alpha particles .......... back from the gold foil, leading to the conclusion that atoms contain a small, dense .......... .
In Rutherford's scattering experiment, a few alpha particles bounced back from the gold foil, leading to the conclusion that atoms contain a small, dense nucleus.
What is the nuclear model of the atom?
The nuclear model describes the atom as having almost all its mass concentrated in a small, positively charged nucleus at its centre, with negatively charged electrons orbiting at a distance.
True or False?
In the Bohr model, the first energy level can hold up to two electrons.
True.
In the Bohr model, the first energy level holds up to 2 electrons, the second holds up to 8 and the third holds up to 8.
Why was the Bohr model accepted as an improvement over the nuclear model?
The Bohr model could explain the absorption and emission of electromagnetic radiation, which the nuclear model could not. Theoretical calculations using the Bohr model also agreed with experimental results.
What are the three subatomic particles found in an atom, and where are they located?
The three subatomic particles are protons and neutrons, which are found in the nucleus, and electrons, which orbit the nucleus.
In an atom, protons and neutrons are found in the .......... , while electrons are found .......... the nucleus.
In an atom, protons and neutrons are found in the nucleus, while electrons are found orbiting the nucleus.
True or False?
The nucleus of an atom contains most of the atom's mass.
True.
The nucleus contains nearly all of the atom's mass because it contains the protons and neutrons, which are much heavier than electrons.
What is an electron?
An electron is a negatively charged subatomic particle that orbits the nucleus of an atom.
The radius of an atom is approximately 1 × 10-10 m, but the radius of its .......... is over 10 000 times smaller.
The radius of an atom is approximately 1 × 10-10 m, but the radius of its nucleus is over 10 000 times smaller.
Why is most of an atom described as empty space?
Most of an atom is empty space because the nucleus is over 10 000 times smaller than the atom itself. The electrons orbiting the nucleus are very far from it relative to its size.
True or False?
Electrons have the same mass as protons.
False.
Electrons have a mass approximately 1/2000 of a proton or neutron. Their mass is effectively negligible compared to the particles in the nucleus.
What is the overall charge of an atom, and why?
An atom has no overall charge because the number of positive protons in the nucleus equals the number of negative electrons orbiting it, so the charges cancel out.
What are the charges of the three subatomic particles?
Protons have a positive charge, neutrons have no charge and electrons have a negative charge.
Define density.
Density is the mass per unit volume of a material.
Density is calculated using the equation ρ = m / V, where ρ is density, m is .......... and V is .......... .
Density is calculated using the equation ρ = m / V, where ρ is density, m is mass and V is volume.
Why can two objects of similar size have very different masses?
Two similarly sized objects can have very different masses because they are made from materials with different densities. A material with a higher density has more mass packed into the same volume.
True or False?
An object with a density greater than 1000 kg/m3 will sink in water.
True.
Water has a density of 1000 kg/m3. Any object with a density greater than this will sink in water.
A metal block has a mass of 500 g and a volume of 200 cm3. Calculate its density.
Using the equation ρ = m / V:
ρ = 500 / 200 = 2.5 g/cm3
The equation for density is ρ = m / V. Rearrange this equation to find mass and volume.
To find mass, rearrange to:\nm = ρ × V\n\nTo find volume, rearrange to:\nV = m / ρ
True or False?
If mass is measured in grams and volume in cm3, the density will be in kg/m3.
False.
If mass is in grams and volume in cm3, the density will be in g/cm3. To get density in kg/m3, mass must be in kg and volume in m3.
A paving slab has a mass of 73 kg and dimensions 0.04 m × 0.5 m × 0.85 m. Calculate its density.
First calculate the volume:
V = 0.04 × 0.5 × 0.85 = 0.017 m3
Then use the density equation:
ρ = 73 / 0.017 = 4300 kg/m3 (2 s.f.)
Why are the densities of solids and liquids roughly the same?
In both solids and liquids, the molecules are tightly packed together. In a liquid, molecules have enough energy to push past each other, but the spacing between them is similar to a solid.
True or False?
Gases have a density approximately 1/1000 of the density of solids or liquids.
True.
In a gas, molecules are widely separated, so the same mass occupies a much larger volume, giving a density about 1/1000 of solids or liquids.
What is the key difference between how particles are arranged in a solid compared to a liquid?
In both states, particles are tightly packed. The key difference is that in a liquid, particles have enough energy to move past each other, while in a solid they are held in fixed positions.
At room temperature, the distance between molecules in a gas is roughly .......... times (in each direction) the distance between molecules in a solid or liquid.
At room temperature, the distance between molecules in a gas is roughly ten times (in each direction) the distance between molecules in a solid or liquid.
True or False?
In a liquid, the molecules are widely separated and move freely.
False.
In a liquid, molecules are tightly packed but have enough energy to push past each other. It is in a gas that molecules are widely separated.
What is the approximate density of air at sea level and room temperature?
The density of air at sea level and room temperature is approximately 1.3 kg/m3. This is roughly 1000 times less than the density of water (1000 kg/m3), because gas molecules are widely spaced apart.
How is the volume of an irregularly shaped object measured in the density experiment?
The volume of an irregularly shaped object is measured using a displacement technique. The object is lowered into a eureka can full of water, and the displaced water is collected and measured in a measuring cylinder.
True or False?
To find the density of a liquid, you should pour the liquid directly into the measuring cylinder while it is on the balance.
False.
You should first measure the mass of the empty measuring cylinder, then fill it with liquid and measure the total mass. The mass of the liquid is found by subtracting the empty mass from the total.
To find the mass of a liquid, subtract the mass of the .......... measuring cylinder from the mass of the measuring cylinder .......... the liquid.
To find the mass of a liquid, subtract the mass of the empty measuring cylinder from the mass of the measuring cylinder containing the liquid.
How is the volume of a regularly shaped object determined in the density experiment?
The volume of a regularly shaped object is calculated from its dimensions (e.g. length, width, height or radius), measured with a ruler, Vernier calipers or micrometer depending on the object's size.
The table below shows three instruments used to measure length in the density experiment. State the resolution of each:
Instrument
Resolution
30 cm ruler
Vernier calipers
Micrometer
The table below shows three instruments used to measure length in the density experiment:
Instrument
Resolution
30 cm ruler
1 mm
Vernier calipers
0.01 mm
Micrometer
0.001 mm
What is a systematic error?
A systematic error is an error that causes all measurements to be shifted in the same direction (all too high or all too low). An example is not zeroing the digital balance before use.
True or False?
Vernier calipers have a higher resolution than a 30 cm ruler.
True.
Vernier calipers have a resolution of 0.01 mm, while a 30 cm ruler has a resolution of 1 mm. A micrometer has an even higher resolution of 0.001 mm.
Why should the digital balance be set to zero before measuring mass?
Setting the digital balance to zero before measuring removes systematic errors. Any residual mass on the balance would shift all readings in the same direction, giving inaccurate density values.
True or False?
Repeat measurements are taken when determining density to reduce systematic errors.
False.
Repeat measurements reduce random errors, not systematic errors. Systematic errors are reduced by correctly calibrating equipment, such as zeroing the balance before use.
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