Define alpha particle .

An alpha particle is the nucleus of a helium atom , made up of two protons and two neutrons, and is positively charged .

What was the experimental setup of the alpha particle scattering experiment?

Alpha particles were fired at a thin gold foil , with a detector positioned around it to measure how many particles were deflected at different angles.

What did the observation that the majority of alpha particles passed straight through the gold foil suggest about the structure of the atom?

The atom is mainly empty space .

What did the deflection of some alpha particles through small angles of less than 10° suggest?

There is a positive nucleus at the centre of the atom, which repels the positively charged alpha particles.

What did the small number of alpha particles deflected through angles greater than 90° suggest about the nucleus?

The nucleus is extremely small and contains almost all of the atom's mass and charge .

Before the nucleus was discovered, atoms were thought to consist of a positive sphere of charge with electrons embedded within it, known as the .......... model.

Before the nucleus was discovered, atoms were thought to consist of a positive sphere of charge with electrons embedded within it, known as the plum pudding model.

True or False? Most alpha particles in Rutherford's scattering experiment were deflected through large angles.

False. The majority of alpha particles passed straight through the foil; only a very small number were deflected through angles greater than 90°, showing that the nucleus occupies a tiny fraction of the atom's volume.

Define nucleus (as part of an atom).

The nucleus is the central part of an atom, containing only the protons and neutrons ; the electrons orbit outside it.

What three types of particles make up the atoms of all elements?

Protons , neutrons and electrons .

Where in an atom are protons and neutrons found, and where are electrons found?

Protons and neutrons are found in the nucleus ; electrons orbit the nucleus.

Why is a stable atom electrically neutral?

A stable atom contains equal numbers of protons and electrons , which carry equal and opposite charge, so the overall charge is zero.

What is the approximate diameter of an atom, and of a nucleus?

The diameter of an atom is about 1 × 10 -10 m; the diameter of a nucleus is about 1 × 10 -15 m.

In the closest approach method, at the point of closest approach the alpha particle's kinetic energy has been entirely converted into electric .......... energy.

In the closest approach method, at the point of closest approach the alpha particle's kinetic energy has been entirely converted into electric potential energy.

What does an alpha particle being scattered straight back from the gold foil in the closest approach method indicate?

There is electrostatic repulsion between the positively charged alpha particle and the positively charged nucleus.

True or False? The nucleus of an atom contains protons, neutrons and electrons.

False. The nucleus contains only protons and neutrons ; the electrons orbit outside the nucleus, making up the rest of the atom.

A nuclide is a group of atoms containing the same number of protons and neutrons .

An isotope is an atom (of the same element) that has an equal number of protons but a different number of neutrons .

In AZX notation, what do the numbers A and Z represent?

A is the nucleon (mass) number : the total number of protons and neutrons. Z is the proton (atomic) number : the total number of protons.

Why are isotopes generally unstable?

Isotopes have an imbalance between the number of protons and neutrons , causing them to decay and emit radiation to reach a more stable form.

Why does a different number of neutrons change an atom's mass but not its chemical properties or charge?

Neutrons are uncharged but have mass, so extra neutrons increase an atom's mass without affecting its charge or chemical behaviour.

Chlorine's mass number is given as 35.5 because it is a .......... average of the mass numbers of its two naturally occurring isotopes.

Chlorine's mass number is given as 35.5 because it is a weighted average of the mass numbers of its two naturally occurring isotopes.

True or False? Isotopes of the same element have different numbers of electrons.

False. Isotopes have the same number of protons (and therefore the same number of electrons ); only the number of neutrons differs.

Define the strong nuclear force .

The strong nuclear force is the force that holds the nucleus together by binding quarks (and hence protons and neutrons) within it, overcoming the electrostatic repulsion between protons.

Why can't gravitational and electrostatic forces alone hold the nucleus together?

Gravity between nucleons is far too weak, while electrostatic repulsion between protons is far too strong; without another force, the nucleus would not hold together.

Over what separation is the strong nuclear force repulsive, and over what separation is it attractive?

The strong nuclear force is repulsive below about 0.5 fm and attractive up to about 3.0 fm.

At what separation does the strong nuclear force reach its maximum attractive value, and why is this significant?

At about 1.0 fm , which is the typical separation between nucleons in a nucleus.

Beyond a separation of about 3.0 fm, the strong nuclear force becomes .......... .

Beyond a separation of about 3.0 fm, the strong nuclear force becomes zero .

True or False? The strong nuclear force has a greater range than the electrostatic force.

False. The strong nuclear force acts only up to about 3.0 fm, a much shorter range than the electrostatic force.

What do the key features of the graph of nuclear radius R against nucleon number A show?

The gradient is steep near the origin and then gradually flattens, showing that nuclear radius increases with nucleon number, but A is not proportional to R .

What does the nuclear density equation show about how density varies with nucleon number A ?

The nucleon number A cancels out of the equation, so nuclear density is constant and independent of nucleon number and radius.

Since nuclear density is constant and independent of radius, this shows that nucleons are evenly .......... throughout the nucleus, regardless of its size.

Since nuclear density is constant and independent of radius, this shows that nucleons are evenly separated throughout the nucleus, regardless of its size.

True or False? Nuclear density increases as the nucleon number of a nucleus increases.

False. The nucleon number A cancels out of the density calculation, so nuclear density is constant for all nuclei, regardless of their size.

A LevelPhysicsOCRFlashcards6. Particles & Medical PhysicsThe Nuclear Atom

The Nuclear Atom (OCR A Level Physics): Flashcards

Exam code: H556

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FrontAlpha Particle Scattering Experiment
Define alpha particle.

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Cards in this collection (36)

Define alpha particle.
An alpha particle is the nucleus of a helium atom, made up of two protons and two neutrons, and is positively charged.
What was the experimental setup of the alpha particle scattering experiment?
Alpha particles were fired at a thin gold foil, with a detector positioned around it to measure how many particles were deflected at different angles.
What did the observation that the majority of alpha particles passed straight through the gold foil suggest about the structure of the atom?
The atom is mainly empty space.
What did the deflection of some alpha particles through small angles of less than 10° suggest?
There is a positive nucleus at the centre of the atom, which repels the positively charged alpha particles.
What did the small number of alpha particles deflected through angles greater than 90° suggest about the nucleus?
The nucleus is extremely small and contains almost all of the atom's mass and charge.
Before the nucleus was discovered, atoms were thought to consist of a positive sphere of charge with electrons embedded within it, known as the .......... model.
Before the nucleus was discovered, atoms were thought to consist of a positive sphere of charge with electrons embedded within it, known as the plum pudding model.
True or False?
Most alpha particles in Rutherford's scattering experiment were deflected through large angles.
False.
The majority of alpha particles passed straight through the foil; only a very small number were deflected through angles greater than 90°, showing that the nucleus occupies a tiny fraction of the atom's volume.
Define nucleus (as part of an atom).
The nucleus is the central part of an atom, containing only the protons and neutrons; the electrons orbit outside it.
What three types of particles make up the atoms of all elements?
Protons, neutrons and electrons.
Where in an atom are protons and neutrons found, and where are electrons found?
Protons and neutrons are found in the nucleus; electrons orbit the nucleus.
Why is a stable atom electrically neutral?
A stable atom contains equal numbers of protons and electrons, which carry equal and opposite charge, so the overall charge is zero.
What is the approximate diameter of an atom, and of a nucleus?
The diameter of an atom is about 1 × 10^-10 m; the diameter of a nucleus is about 1 × 10^-15 m.
In the closest approach method, at the point of closest approach the alpha particle's kinetic energy has been entirely converted into electric .......... energy.
In the closest approach method, at the point of closest approach the alpha particle's kinetic energy has been entirely converted into electric potential energy.
What does an alpha particle being scattered straight back from the gold foil in the closest approach method indicate?
There is electrostatic repulsion between the positively charged alpha particle and the positively charged nucleus.
True or False?
The nucleus of an atom contains protons, neutrons and electrons.
False.
The nucleus contains only protons and neutrons; the electrons orbit outside the nucleus, making up the rest of the atom.
Define nuclide.
A nuclide is a group of atoms containing the same number of protons and neutrons.
Define isotope.
An isotope is an atom (of the same element) that has an equal number of protons but a different number of neutrons.
In AZX notation, what do the numbers A and Z represent?
A is the nucleon (mass) number: the total number of protons and neutrons. Z is the proton (atomic) number: the total number of protons.
Why are isotopes generally unstable?
Isotopes have an imbalance between the number of protons and neutrons, causing them to decay and emit radiation to reach a more stable form.
Why does a different number of neutrons change an atom's mass but not its chemical properties or charge?
Neutrons are uncharged but have mass, so extra neutrons increase an atom's mass without affecting its charge or chemical behaviour.
Chlorine's mass number is given as 35.5 because it is a .......... average of the mass numbers of its two naturally occurring isotopes.
Chlorine's mass number is given as 35.5 because it is a weighted average of the mass numbers of its two naturally occurring isotopes.
True or False?
Isotopes of the same element have different numbers of electrons.
False.
Isotopes have the same number of protons (and therefore the same number of electrons); only the number of neutrons differs.
Define the strong nuclear force.
The strong nuclear force is the force that holds the nucleus together by binding quarks (and hence protons and neutrons) within it, overcoming the electrostatic repulsion between protons.
Why can't gravitational and electrostatic forces alone hold the nucleus together?
Gravity between nucleons is far too weak, while electrostatic repulsion between protons is far too strong; without another force, the nucleus would not hold together.
Over what separation is the strong nuclear force repulsive, and over what separation is it attractive?
The strong nuclear force is repulsive below about 0.5 fm and attractive up to about 3.0 fm.
At what separation does the strong nuclear force reach its maximum attractive value, and why is this significant?
At about 1.0 fm, which is the typical separation between nucleons in a nucleus.
Beyond a separation of about 3.0 fm, the strong nuclear force becomes ...........
Beyond a separation of about 3.0 fm, the strong nuclear force becomes zero.
True or False?
The strong nuclear force has a greater range than the electrostatic force.
False.
The strong nuclear force acts only up to about 3.0 fm, a much shorter range than the electrostatic force.
What is another name for the strong nuclear force?
The strong interaction.
Define R₀ in the equation for nuclear radius.
R₀ is the constant of proportionality in $R = R_{0} A^{1 / 3}$ , equal to 1.2 fm (1.2 × 10^-15 m) — approximately the radius of a proton.
What equation relates nuclear radius R to nucleon number A?
$R = R_{0} A^{1 / 3}$ where R₀ is a constant of proportionality (1.2 fm).
What do the key features of the graph of nuclear radius R against nucleon number A show?
The gradient is steep near the origin and then gradually flattens, showing that nuclear radius increases with nucleon number, but A is not proportional to R.
What does the nuclear density equation show about how density varies with nucleon number A?
The nucleon number A cancels out of the equation, so nuclear density is constant and independent of nucleon number and radius.
Since nuclear density is constant and independent of radius, this shows that nucleons are evenly .......... throughout the nucleus, regardless of its size.
Since nuclear density is constant and independent of radius, this shows that nucleons are evenly separated throughout the nucleus, regardless of its size.
What is the order of magnitude of a typical nuclear radius?
Around 10^-15 m (1 fm).
True or False?
Nuclear density increases as the nucleon number of a nucleus increases.
False.
The nucleon number A cancels out of the density calculation, so nuclear density is constant for all nuclei, regardless of their size.

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