Atomic Stricture Flashcards
What is the radius of an atom
Radius of nucleus
What does this tell us
1x10-10
1/10000 smaller than the atom
This tells us that most of the atom is empty space
How are electrons structures
I’m energy shells electromagnetic radiation is able to give electrons energy to move to a higher energy level further away from the nucleus
Charge of an atom
Neutral
What is an isotope
Different forms of the same element with the same number of protons and electrons but different number of neutrons
Ions
Lost electrons - positive
Gained electrons - negative
History of the model of the atom
Spheres that couldn’t be divided any further
Electrons were discovered and the plum pudding model was theorised suggesting the atom is a ball of positive charge with electrons embedded as the atoms had a neutral charge electrons were evenly distributed under a positive dough
Rutherford’s experiment
Rutherford carried out an experiment where he fired alpha particles at a thin piece of gold foil
Most alpha particles passed straight through
Some were deflected
1 in 1000 were rebounded
This means
Majority of the atom is empty space
There must be a concentration of a charge
Charge must be positive majority of the atoms mass is in one place
Nuclear model
Niels Bohr adopted the nuclear model by suggesting electrons orbit the nucleus at specific distances
How atoms emit radiation
Atomic nuclei eg isotopes can be unstable they have an imbalance of protons and neutrons,
The nucleus gives out radiation as it changes to become more stable. This is radioactive decay and it’s a random process.
Radioactive decay
Unstable isotopes decay into other elements and give out radiation as they try to become more stable
Ionising radiation
Radiation that knocks off electrons creating positive ions
The ionising power of a radiation source is how easily it can do this
Three types of ionising radiation
Alpha
Alpha particle emitted from nucleus
Two neutrons and two protons
Alpha particles ionise atoms when they collide into them ( they knock electrons off them)
Don’t penetrate very far into materials
Only travel a few cm in air
Absorbed by paper
Because of size they are strongly ionising
Used in smoke detectors by ionising air particles and allowing a current to flow
If there’s smoke it binds to the ions and current stops
Beta
Fast moving electrons released by the nucleus
Moderately ionising
Moderately penetrating materials
Few metres in air
Absorbed by sheets of aluminium
For every beta particle emitted a neutron in the nucleus turns into a proton
Used to test thickness of sheets of metal
Gamma
Waves of electromagnetic radiation released by the nucleus
Penetrate far into materials
Long distance through air
Weakly ionising tend to pass through rather than collide with atoms
Absorbed by sheets of lead or concrete
Half life
Half life of a radioactive isotope is the time it takes for the number of nuclei in the isotope in a sample to halve
