Atomic Structure Flashcards
What is the radius of an atom?
1x10^-10 m
Charges of the subatomic particles
proton= +1
neutron= 0
electron= -1
Masses of the subatomic particles
proton= 1
neutron= 1
electron= 0
What happens to electrons when something absorbs electromagnetic radiation?
the electrons are moved to a higher energy level, further from the nucleus
What happens to electrons when something emits electromagnetic radiation?
the electron drops to a lower energy level, closer to to the nucleus
Positive ion
when an atom has LOST an electron
Negative ion
when an atom has GAINED an electron
What do all atoms of an element have the same of?
proton number (atomic number)
Mass Number
number of protons and neutrons in a nucleus
Atomic Number
Number of protons
Isotopes
atoms of an element that have the same number of protons, so are from the same element, but they have a different number of neutrons
Plum pudding model
the atom is a ball of positive charge with negative electrons embedded in it.
Gold Foil Experiment: Results
most passed straight through
some were deflected so they must have been repelled by the same charge that the alpha particle carried
the repelling charge must have been heavier than the alpha or it would have passed straight through
Gold Foil: Conclusions
mass of the atom in in a central, positively charged nucleus
the electrons surround the nucleus
Role of Neils Bohr
adapted the model by suggesting that electrons orbit the nucleus at set distances
The results of the later experiments
the positive charge of the nucleus can be divided into a whole number of smaller particles, each with the same amount of positive charge, commonly known as protons
Role of James Chadwick
1932
carried out a number of experiments which provided evidence that in the nucleus there was also a particle called the neutron
Which type of nuclei, decay, and why?
Unstable nuclei give out radiation to become more stable
Activity
the rate at which something decays
What is activity measured in?
Becquerels
One Becquerel=
One decay per second, one count rate per second
Count rate
the number of decays per second
3 types of nuclear decay
alpha, beta, gamma
Alpha
- 2 protons, 2 neutrons
-strong ionising power
-absorbed by a few cm of air/paper
-can cause damage to living cells
Beta
- high-speed electron, ejected from the nucleus which turns into a proton and electron, of which the electron is emitted
- reasonable ionising power
-absorbed by a few mm of aluminium
-can cause damage to cells if absorbed
-can penetrate into organs
Gamma
- Electromagnetic radiation
-poor ionising power
-absorbed by many cm of lead/many m of concrete - can pass through cells without being absorbed
Radioactive contamination
unwanted presence of materials containing radioactive atoms on other materials
Irradiation
The process of exposing an object to nuclear radiation
Deliberate/Accidental
Does not cause the object to become radioactive
Ways of protecting from unwanted radiation
use sources with the lowest activity for the shortest time
wear appropriate clothing, e.g. lead apron
no handling sources with bare hands
Hazards of contamination
Food contaminated with an alpha source would be more hazardous than if it had gamma radiation
An area contaminated with alpha would not be dangerous unless it was entered, due to the low penetration of alpha radiation
However, if it was contaminated with a source of gamma radiation, this would irradiate people nearby
Half-Life
-the time it takes for half the nuclei to decay
-time taken for the half-life to fall to 50%
Alpha in the nuclear equation
Mass is reduced by 4
The atomic number is reduced by 2
Beta in the nuclear equation
mass remains the same
the atomic number is increased by 1
