4. Atomic Structure (structure and development of the atom, nuclear equations, nuclear radiation properties) Flashcards
What did John Dalton do (1804)?
He believed that atoms were tiny spheres that could not be broken down
What did JJ Thompson do (1904-1905)?
Thompson discovered electrons, so he said atoms were a ball of positive charge with electrons scattered in the atom (plum pudding model)
What is Rutherford (1909)?
Rutherford and Marsen did the scattering experiment and realised most of the atom is empty space
What are the observations and conclusions of the alpha particle scattering experiment?
Most went straight through so most of the atom is empty space
Some deflected less than 90 degrees meaning that the nucleus is positively charged
Few deflected more than 90 degrees so most of the mass is in the nucleus
What are the subatomic particles charge and mass?
Electron: -1, 1/2000
Proton: +1, 1
Neutron: 0, 1
What are isotopes?
A different version of the same element with the same number of protons different numbetr of neutrons
What is radioactive decay?
when a nucleus decays, it is a random process
What are the 4 types of decay?
- Alpha decay
- Beta decay
- Gamma decay
- Neutron decay
What is radioactive substance?
Is an unstable nucleus which becomes stable from releasingly radiation
What is alpha radiation?
- An alpha particle is a helium nucleus
- An alpha particle has 2 protons and 2 neutrons
- When a nucleus emits (gets rid of) on an alpha, it loses 2 of its neutrons and 2 of its protons
- So mass number decreases by 4
- Atomic number decreases by 2
What happens to the mass number and atomic number in alpha decay?
- The mass number decreases by 4
- Atomic decreases by 2
What is beta decay?
when a beta particle is emitted from the nucleus when a neutron turns into a proton
What happens to the mass number and atomic number in beta decay?
- The mass number stays the same
- The atomic number increases by 1
What is gamma decay?
- Gamma rays are electromagnetic waves, with a short wave length and a high frequency
- Because rays are electromagnetic waves, they don’t have a mass or charge
- When a nucleus emits a gamma ray its mass and atomic number don’t change
When do gamma rays occur?
- When a nucleus is in its excited state
- When an excited nucleus emits a gamma ray it moves to a lower energy level
What is an alpha particles charge?
+2
What is a beta particles charge?
-1
What is a gamma particles charge?
0
What is an alpha particles range in air?
Few cms in air
What are beta particles range in air?
A metre
What are gamma particles range in air?
Infinite
What is alpha particles penetration stopped by?
Stopped by paper
What are beta particles penetration stopped by?
Stopped by a few mm of aluminium
What are gamma particles penetration stopped by?
Reduced by a few mm of lead
What are alpha particles ionisation?
High
What are beta particles particles ionisation?
Medium
What are gamma particles ionisation?
Low
What is ionising power?
Turning other atoms in ions by ‘knocking’ their electrons. Determined by charge and size
What is Ionisation?
Any process from where atoms are charged
What is a beta particle?
A beta particle is a fast moving electron