Atomic Structure Flashcards
What is an Isotope?
> They are atoms with the same number of protons but different number of neutrons.
What happens to unstable isotopes?
> They tend to decay into other elements and give out radiation as the try to become stable.(Radioactive Decay).
How do we know if EM radiation is absorbed?
When electrons move to a higher orbit (further from the nucleus)
How do we know if EM radiation is Emitted?
When the electrons falls to a lower orbit (closer to the nucleus)
What happens if an electron gains enough energy
It can leave the atom to form a positive ion.
What did Dalton propose?
Dalton said everything was made of tiny spheres (atoms) that could not be divided.
What did JJ Thompson do?
> The overall charge of an atom is neutral, so
the negative electrons were dispersed
through the positive “pudding” to cancel
out the charges.
What were the observations of the alpha particle scattering experiment?
Most 𝛼 particles went straight through:
->So most of atom is empty space
Some 𝛼 particles were slightly deflected:
>So nucleus must be charged, deflecting positive 𝛼
> Few 𝛼 particles were deflected by >90°:
- So nucleus contained most of the mass
What did Rutherford Propose?
> There is a positive nucleus at the
centre of the atom, and negative electrons
existing in a cloud around the nucleus
Later on what was introduced?
> Positive charge of nucleus could be subdivided into smaller particles, each with the same
amount of charge – the proton
->20 years after the ‘nucleus’ was an accepted scientific idea, James Chadwick provided
evidence to prove neutrons existed (don’t need specifics)
What is radioactive decay?
Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable.
What is Alpha particles and its characteristics?
Alpha α (a helium nucleus)
Highly ionising
Weakly penetrating
(~5cm of air)
What is Beta particles and its characteristics?
o Beta Minus β (electron)
Medium ionising
Medium penetration
(~50cm of air, sheet of paper)
What is Gamma radiation and its characteristics?
Gamma γ (radiation)
Low ionising
Highly penetration
(very far in air, few cm of lead)
What is the nuclear equation for Alpha Particle?
—4
A
2
What is the nuclear equation for Beta Particle?
—0
B Not minus 0, but is -1.
-1
Why don’t gamma rays change the charge of their nucleus?
> They have no charge.
What is Half-Life
The half-life of an isotope is the time taken for half the nuclei in a sample to decay or the
time taken for the activity or count rate of a sample to decay by half.
What happens in a short half life
o The source presents less of a risk, as it does not remain strongly radioactive
o This means initially it is very radioactive, but quickly dies down
o So presents less of a long-term risk
What happens in a Long half-life
> The source remains weakly radioactive for a long period of time.
o It is suitable because it will not need to be replenished, and its weak activity means it won’t be harmful to anyone.
Explain why contamination of the inside of the human body by a radioactive material that emits alpha radiation is highly dangerous.
alpha radiation is highly ionising
causing an increased risk of cancer
until the radioactive material is removed / excreted
Why is it safe to use a source of alpha radiation in a house?
beta and gamma radiation will penetrate smoke
no change (in the count rate) would be detected
Explain the ideal properties of a radioactive source for use in medical diagnosis
alpha radiation is not very penetrating
The smoke alarm would not work with a radiation source that emits beta or gamma radiation.
Explain why.
* short half-life or half-life of a few hours
* less damage to cells / tissues / organs body
* low ionising power
* less damage to cells / tissues / organs / body
* highly penetrating
* it can be detected outside the body
* emits gamma radiation
