P1 - Atomic structure Flashcards
What did Democritus think about the model of the atom?
He thought all matter was made up of identical lumps called atomos.
When Democritus come up with his atom model theory?
5th century BC Greece
What did John Dalton think about the model of the atom?
That matter was made up of atoms that couldn’t be broken up, and that each element was made up of a different type of atom.
When did John Dalton come up with his atom model theory?
1804
What did J.J. Thomson think about the model of the atom?
He discovered particles called electrons that could be removed from atoms. He suggested that atoms where spheres of positive charge with negative electrons embedded in them, it was called the plum pudding model.
When did J.J. Thomson come up with the plum pudding model?
1904
What was the Alpha scattering experiment?
They fired a beam of alpha particles at thin gold foil. Based on the plum pudding model they expected the particles to pass straight through the gold sheet or be slightly deflected. Some particles did go straight through the sheet but some where deflected more than than expected and a few were deflected back the way they had come.
What did Ernest Rutherford and his students think about the model of the atom?
Because a few alpha particles were deflected back they realised most of the mass of the atom must be concentrated at the centre in a tiny nucleus. This nucleus must also have positive charge as it repelled the positive alpha particles. As nearly all passed through, most of the atom is empty space. They had discovered the first nuclear model of the atom.
When did Rutherford conduct the alpha scattering experiment?
1909
What was the nuclear model that developed from the alpha scattering experiment?
A positively charged nucleus surrounded by a cloud of negative electrons.
What did Niels Bohr say about the atom model?
Electrons orbiting the nucleus do so at certain distances called energy levels. Futher experiments caused him to change it to a nucleus made up of a group of protons.
When did Niels Bohr make his discoveries?
Early 1900 after Rutherford
What did James Chadwick do?
Proved the existence of the neutron which explained the imbalance between the atomic and mass numbers.
When did James Chadwick discover the neutron?
1932
Current model of the atom
In book
What is an isotope?
atoms with the same number of protons (atomic number) but a different number of neutrons (different mass number)
Outline the process of radioactive decay
Unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable
Name the three types of ionising radiation
gamma γ
alpha α
beta β
Where does ionising radiation come from?
Radioactive substances emit it from their nucleus
Other than radiation, what do radioactive substances emit?
Neutrons (when they decay) as they balance their atomic and mass numbers
What does ionisng radiation do?
It knocks electrons off atoms, creating positive ions. Ionising power of a radiation source is how easy it is to do this.
What are alpha particles?
Helium nuclei
What is alpha radiation?
When an alpha particle is emitted from the nucleus
What is an alpha particle made up of?
Two neutrons and two protons
