P4 Atoms & Radiation

How much smaller is the atomic nucleus, compared to the whole atom?

10 000 times smaller

What is the basic structure of an atom?

a positively charged nucleus composed of both protons and neutrons surrounded by electrons

What happens when electrons gain energy by absorbing electromagnetic radiation?

They move to a higher energy level (further from the nucleus)

What happens when electrons lose energy by releasing electromagnetic radiation?

They move to a lower energy level (closer to the nucleus)

How are the number of protons and electrons related in an atom?

same number of protons and electrons

How do atoms turn into positive ions?

by losing electrons

What is the atomic number of an atom?

the number of protons in an atom

What is the mass number of an atom?

the total number of protons and neutrons in an atom

What are isotopes?

atoms which have the same number of protons but a different number of neutrons

𝗕𝗲𝗳𝗼𝗿𝗲 the discovery of electrons, what was the model of the atom? (2)

Atoms were tiny spheres that could not be divided.

Each element was made of a different type of sphere.

𝗔𝗳𝘁𝗲𝗿 the discovery of electrons, what was the model of the atom?

Plum pudding model: atoms are balls of positive charge, with negative electrons embedded in them

What is the nuclear model of the atom?

The atom has a nucleus which contains most of the mass and is charged

What was Bohr's contribution to the model of the atom? (2)

Electrons orbit the nucleus at specific distances (called energy levels)

His theoretical calculations agreed with experimental observations

What was Chadwick's contribution to the model of the atom? (2)

He provided the evidence to show the existence of neutrons in the nucleus

This was about 20 years after the nucleus became an accepted scientific idea

Who calculated that electrons had fixed orbits?

Bohr

Who provided the evidence to show neutrons existed?

Chadwick

After the scattering experiment, how did ideas about the nucleus develop?

The nucleus' positive charge was carried by more than one particle, which were named protons

How was the alpha scattering experiment conducted?

Scientists fired a beam of alpha particles at a thin sheet of gold foil and recorded where they went

What were the results of the alpha scattering experiment? (4)

most went straight through
some were deflected
some bounced back
the plum pudding model couldnt explain these findings

In the alpha scattering experiment, a few alpha particles were deflected right back and some were deflected more than expected. What did the scientists deduce from this? (2)

Most of the atom's mass was concentrated in a central nucleus

The nucleus must be charged

In the alpha scattering experiment, most of the alpha particles passed straight through. What did the scientists deduce from this? (2)

Most of the atom is just empty space, rather than a solid sphere

The nucleus is very small relative to the size of the atom

What changes were made to the atomic model based on evidence from the alpha scattering experiment?

Most of the atom's mass was concentrated in a central nucleus, which is charged

What happens when new experimental evidence can't be explained by an existing scientific model?

The model may be changed or replaced

What do unstable isotopes tend to do? (2)

They give out radiation from the nucleus as they change to become more stable

This process is called radioactive decay

What is radioactive decay?

The nucleus gives out radiation as it changes to become more stable

What types of radiation can unstable nuclei release?

Alpha, beta, gamma, neutrons

What is alpha radiation?

two neutrons and two protons; it is the same as a helium nucleus

What is the symbol for alpha?

α

What is the mass and charge of alpha particles?

Relative mass: 4. Charge: +2

What is the ionising power of alpha radiation?

High

What is the range of alpha particles in air?

Low; a few centimetres

What materials stop alpha radiation?

Paper or skin (and anything thicker or denser than these)

What is beta radiation?

a high speed electron ejected from the nucleus as a neutron turns into a proton

What is the symbol for beta?

β

What is the relative mass and charge of beta particles?

RM: Neglegible
RC: -1

What is the ionising power of beta radiation?

Moderate

What is the range of beta radiation in air?

several metres

What materials stop beta radiation?

Thin sheet of aluminium (and anything thicker or denser than this)

What is gamma radiation?

electromagnetic radiation from the nucleus

What is the symbol for gamma?

γ

What is the mass and charge of gamma rays?

RM: 0
RC: 0

What is the ionising power of gamma radiation?

Low

What is the range of gamma radiation in air?

Very high: it is not stopped by air

What materials reduce gamma radiation? (2)

Several centimetres of lead or several metres of concrete

It isnt stopped completely

What is a use of alpha radiation sources?

Smoke alarms

What is a use of beta radiation sources?

Testing the thickness of sheets of metal

How are beta and gamma sources used as medical tracers?

A radioactive source is injected or swallowed, and the beta or gamma emitted is followed by a detector

How can radiation be measured?

With a Geiger-Muller tube and counter, which records the count-rate

What is the activity of a radioactive source? (2)

how many decays happen per second

it is measured in becquerels (Bq)

What is the half-life of a radioactive isotope?

the time taken for the number of radioactive nuclei in a sample to halve

What is contamination?

The presence of radioactive sources in/on an object

What is irradiation?

Exposure to radiation

What precautions are used to prevent contamination? (3)

Gloves

Tongs

Protective suits

What precautions are used to prevent irradiation? (2)

Keeping sources in lead-lined boxes

Staying behind barriers/in a different room

What is ionisation?

When atoms gain or lose electrons and become charged

What can ionisation of living cells lead to?

Mutations which can cause cancer or cell death

Which type of radiation is the most ionising?

Alpha

What is peer review?

when research is evaluated by other scientists (who are experts in that area of science) before it is published

Why is it important that findings of studies into radiation are published?

so that people have enough information about the risks and benefits to make informed choices