11 PHYSICS

What is a model

Models are a way of representing a system/ object in order to explain observable phenomena. However, they don't necessarily represent all models

How was the model of the atom evolved throughout the years

Ancient Greeks - Democritus - Dalton - Thompson - Rutherford

What was discovered through Rutherford's model of the atom

- most of the mass of an atom is concentrated in the nucleus

- the nucleus is surrounded by electrons in mostly empty space

What is the charge of an electron?

Negatively charged

What do electrons do in relation to the nucleus?

Orbit the nucleus

How does the mass of an electron compare to protons and neutrons?

Much smaller in mass

What is the relationship between the number of electrons and protons in an atom?

The number of electrons equals the number of protons

Nucleus

the centre of the atom

What are protons and neutrons collectively known as

nucleons

What is the charge of a neutron?

neutral (no charge)

What is the charge of a proton?

positive charge

What symbol represents the atomic number and what does it show

Z, number of protons

What symbol represents the neutron number and what does it show

N, number of neutrons

What symbol represents the mass number and what does it show

A, number of nucleons

Isotopes

Isotopes of an element have the same atomic number but different mass numbers (same number of protons but different number of neutrons)

What force binds nucleons together in the nucleus?

The strong nuclear force

What is the range of the strong nuclear force?

Approximately 5 femtometers (5 x 10^-15 m)

Why do protons in the nucleus repel each other?

Due to electrostatic repulsion of like charges

How do neutrons contribute to nuclear stability?

They help to spread out protons, balancing electrostatic repulsion

What happens if there are too many or too few neutrons in a nucleus?

It results in an unstable nucleus

What is the relationship between nucleus size and neutron quantity?

Larger nuclei require more neutrons to space out protons

What is radioactive decay

When an unstable nuclide emit mass and/or energy to become more stable

What are the 4 common types of radioactive decay

alpha decay, beta positive decay, beta negative decay and gamma decay

What is an alpha decay

the release of an alpha particle from the nucleus (i.e. a helium - 4 nucleus; 2 protons, 2 neutrons)

What is gamma radiation

energy in the form of a photon

What is beta positive decay

the release of a positron from the nucleus when a proton transmutates into a neutron, a positron and an electron neutrino

What is beta negative decay

the release of an electron from the nucleus when a neutron transmutates into a proton, an electron and electron antineutrino

What is gamma decay

protons and neutrons shift/ settle into a more stable arrangement and release a gamma ray (i.e. a pocket of energy)

In context with the stable nuclides graph, where are beta negative decay emitters located

above stable isotope line

In context with the stable nuclides graph, where are beta positive decay emitters located

below stable isotope line

In context with the stable nuclides graph, where are alpha decay emitters located

larger isotopes beyond stable isotope line

What is the size and charge of an alpha particle

large, +2 (2p, 2n)

What is the size and charge of a beta particle

very small, -1 or +1 depending on which decay

What is the size and charge of a gamma particle

massless (photon of energy), no charge

What is the penetrating ability of an alpha particle

low - can be stopped by a paper or a few cm of air

What is the penetrating ability of a beta particle

high - can be stopped by a few cm of aluminium

What is the penetrating ability of a gamma particle

very high - can not be stopped by a metre of lead

What is the ionising ability of an alpha particle

high - large mass so high kinetic energy and more frequent interactions with target atoms

What is the ionising ability of a beta particle

low - small mass so less kinetic energy than alpha and less frequent interaction with target atom

What is the ionising ability of a gamma particle

very low - doesn't readily interact with matter as it is massless and has no charge

What is the ionising ability

removing electrons from atom

What does the sum of atomic numbers on the left hand side have to equal

the sum of the atomic numbers on the right hand side

What does the sum of mass numbers on the left hand side have to equal

the sum of the mass numbers on the right hand side

What happens when an unstable nuclide decays?

The daughter nuclide produced is usually unstable as well.

What occurs after an unstable nuclide decays?

A series of decays will occur until a stable nuclide is produced.

Can the rate of decay be measured?

The decay of an individual nuclide is a random event. However, in a large sample of radioactive nuclides, the rate of decay can be measured and it is dependent on the number of radioactive nuclides remaining

What is a half life

Half life is the time take :

- for half of the radioactive nuclides to decay

- for the activity to decrease by half

- for the mass of the sample to halve

How long do half lives take

Half lives can be as short as µs or ns, or as long as 10^6 or 10^8 years

What kind of graph is the half life graph

It is exponential

What is the formula for radioactive decay

N = No (1/2)^n

where:

n --> no. of half - lives

No -->the initial amount of substance

N --> The final amount of substance

What is binding energy

- the energy needed to keep all of its nucleons bound in the nucleus

- the energy required to completely separate its nucleons

- Whether or not an isotope is stable depends on its binding energy

Is the mass the same when nucleons are separated and bound together

When nucleons are separated, their total mass is greater than the mass of the nuclide when they are bound togetherT

Mass Defect

Difference in masses resulting from the energy needed to separate the nucleons.

Energy Conversion

The energy needed to separate the nucleons is converted to mass.

What is the formula to calculate mass defect

Change in mass = sum of mass of nucleons - mass of nuclides

What is Einstein's mass - energy equivalence

E = mc^2

E --> binding energy in J

Change in m --> mass defect in kg

c --> speed of light in a vacuum in ms^-

Why do we use the atomic mass unit and what is it equivalent to

Masses on the atomic and subatomic scales are extremely small so instead we use atomic mass units. 1u is the equivalent of 1/12 of the mass of a carbon - 12 nuclide

Why do we use electrovolt

Energies on atomic scales are extremely small. Instead, we use electrovolt, eV

What is an electrovolt

the energy require to move an electron through a potential difference

What is the formula for total nucleon mass M(t)

atomic number (Z) x proton mass m(p) + neutron number (N) x neutron mass m(n)

What is the formula for mass defect

Total nucleon mass m(t) - nuclear mass m(n)

What is the formula for binding energy

E = change in mass x c^2

How to change the binding energy in J to eV

divide it by 1.602 x 10^-19

How to convert from eV to MeV

divide it by 10^6

How does binding energy relate to mass number?

Binding energy increases with mass number.

Does high binding energy guarantee isotope stability?

No, a high binding energy does not guarantee an isotope will be stable.

What characteristic do stable isotopes have regarding binding energy?

Stable isotopes have a higher binding energy per nucleon.

What happens to binding energy per nucleon during nuclide decay?

Every time a nuclide undergoes a decay, the binding energy per nucleon increases.

What does it mean by "artificial"

not natural, man made

What is a transmutation

the process by which a nuclide changes, by nuclear interactions, into an isotope of another element

What are the 2 types of transmutations and examples

Natural - Radioactive decay

Artificial - Fission (splitting apart) and fusion (joining together

What is nuclear fission

The process by which a neutron bombards a large nucleus, forming two or more smaller daughter nuclides, as well as releasing neutrons and energy

What can product neutrons do in nuclear fission?

They can bombard other nuclides, starting a chain reaction.

What is a controlled nuclear fission?

Nuclear reactors.

What is an uncontrolled nuclear fission?

Nuclear bomb.

What is the binding energy of daughter nuclides compared to the original nuclide?

Daughter nuclides have a higher binding energy per nucleon.

What usually happens to daughter nuclides?

They are usually unstable and will undergo radioactive decay.

What is nuclear fusion

The process by which two smaller nuclides combine together to form one heavier nuclide (and often other subatomic particles)

How does the two positive nuclides overcome electrostatic repulsion

In order to overcome electrostatic repulsion between the two positive nuclides so that they are close enough for the strong nuclear force can act on them, very high energies are needed

What are some examples of high energies

high temperature and/ or high pressure

What are some examples of uncontrolled nuclear fusion

- the sun and stars

- hydrogen bomb (H- bomb)

What are some examples of controlled nuclear fusion

not yet achievable on Earth

What is the binding energy per nucleon of products from fusion compared to reactants?

Higher

What happens to elements larger than iron in terms of fusion?

They won't fuse as the binding energy per nucleon decreases.

What must happen for fusion of elements larger than iron to occur?

Energy must be added.

In what event does the energy needed for fusion of elements larger than iron occur?

In a supernova.

How do you calculate the energy from fission and fusion

The difference in mass between reactants and products x 931.5 - finds energy in MeV

Which releases more energy per kg - fusion or fission

fusion

Which produces more energy per event - fusion or fission

fission

What is the formula to calculate the energy produced

E (energy in Joules)/ m (mass in kg)

What is matter composed of

small particles

What kind of motions are particles in

constant random

What kind of movements does solids have

vibration

What kind of movements does liquid have

rotation and some translation

What kind of movements does gas have

translation and some rotation

How can you describe collision between particles

perfectly elastic- no loss of kinetic energy

What is kinetic energy

the energy of motion

What is temperature

a measure of the average kinetic energy of particles in a substance usually expressed on a comparative scale

What is thermal energy

the total kinetic energy of particles in a system

Which has more thermal energy: a bath of warm water or a cup of boiling water

A bath of warm water