Atomic Structure Flashcards
Explain the history of the atom
John dalton- Niel Bohr
1804 John Dalton agreed with democritus that matter was made up of tiny spheres that couldn’t be broken up
JJ Thomson discovered particles called electrons that could be removed from atoms. He suggested that atoms were a spheres of positive charge with negative electrons embedded inside of it- plum pudding model
1909 Rutherford fired a beam of positive alpha particles at a thin gold foil (alph particle scattering experiment. They expected most particles to pass though with some deflected however some were reflected and deflected more then expected. Scientist found out that most of the mass is concentrated in the nucleus. Atom is mostly smpty space
Nuclear model created from alpha particle scattering experiment. Electrons orbit the nucleus at certain energy levels-Niels Bohr
In 1932 Jame Chadsick proved the existence of the neutron explained the imbalances between atomic and mass numbers
Explain then current model of the atom
Nucleus is tiny and contains positive protons and neutral neutrons.
The mass is concentrated in the nucleus and its radius is 10,000 time smaller then the radius of the atom
Negative electrons orbit the nucleus at set energy levels. Radius of atom is 1x10^-10m
Number of protons= number of electrons
Electrons can enter of leave the outermost shell to form a positive or negative ion
What are isotopes
Atoms of the same elment with the same number of protons but different number of neutrons
What is radioactive decay
When unstable istopes give out radiation as they try to become stable.
Name the different types of radiation
Alpha,beta and gamma
What is ioning radiation and power
Radiation that knocks electrons krf atons, creating positive ions
The ionising power of a radiation source is how easily it can do this^
What are alpha particles and its properties
Two neutrons and two protons (helium nucleus)
Don’t penetrate far into material (absorbed by paper)
Travel a few cm in air
What are beta particles and its properties
Simple fast moving electron released by the nucleus.
Mass of 0 and a charge of -1
They are absorbed by aluminium (5mm)
Travel a metres in air
What are gamma particles and its properties
Waves of the electromagnetic radiation released by the nucleus.
They are absorbed by the nucleus (thick sheets of lead or metres of concrete)
Travel long distances in air
How do alpha/beta/gamma particles react in a nuclear equation
Alpha: 2 protons and neutrons atomic and mass number reduced
Uranium-238. _____> Thorium 234 + 4 helium
92 90. 2
Beta: Mass number 0 and atomic number -1. The atomic number increases by 1
Carbon 14________> Nitrogen 14 +. 0 electron
6. 7. -1
Gamma rays: Get rid of excess energy from a nucleus. No change to the atomic mass or atomjc number of the atom
How can radiation be measured
Meausred with a Geiger-Muller counter records the count rate of the number of radiation per second
What is half life
The time it takes for the amount of radiation to emitted by a source to galve
What can half lif be used for
To measure the rate at which a source decays- its activity is measured in becauerels (Bq)
Calcuate this equation:
The intual activity of a sample is 640bq. Calcuate the final activity as a percentage of the intial activity after two halve-lives
1) Find the activity of each have live 1 half-life= 640/2=320
2) Divide the final activity by the intial activity then mutiply by 100 to make a percentage
2 halve-lives = 320/2=160
160/640=ansX100= 25%
Uses of alpha,beta amd gamma particles
Alpha: used in smoke detectors- it ionises air particles causing a current to flow. If smoke is present, it binds ri the ions -cureent stops and alarm goes off
Beta: Emitters used to test thickness of sheets of metal, do no penetrate too far or little
Gamma: used to treat people with cancer- kills living cells and be used as a medical tracer
