Please enable JavaScript.
Coggle requires JavaScript to display documents.
Atomic Structure - Coggle Diagram
Atomic Structure
History of the Atom
Dalton
Dalton's atomic model
- all matter composed of atoms
- while all atoms of an element were identical, different elements had atoms of differing size and mass
- Dalton found an atomic theory of matter could elegantly explain this common pattern in chemistry
- found in 1803
J.J. Thompson
plum pudding model
- Thompson's model showed an atom that had a positively charged medium or space, with negatively charged electrons indies the medium
- found in 1904
- Thompson's experiment with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons
Bohr
Bohr's discovery of electrons
- in 1913, Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities
- electrons should move around the nucleus but only in prescribed orbits
- when jumping from one orbit to another with lower energy a light jumping quantum is emitted
Rutherford
Rutherford's scattering experiment
- positively charged alpha particles were fired at thin gold foil.
- most alpha particles went straight through the foil, but a few were scattered in different directions
- in 1909, Rutherford designed an experiment to test the plum pudding model
Chadwick
Chadwick's discovery of neutrons
- by 1920, physicists knew that most of the mass of the atom was located in a nucleus as its centre, and that its central core contained protons
- in May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron
Radiation
Beta
- a Beta particle consists of an electron emitted when a neutron in the nucleus turns into a proton
- a Beta particles relative mass is effectively 0 and relative charge is -1
Gamma
- Gamma radiation is a high energy, high frequency wave
- Gamma radiation has no mass and no charge as it is a wave
Alpha
- an Alpha particle consists of 2 protons and 2 neutrons
- an Alpha particles relative mass is 4 and relative charge is +2
Radioactivity
- if an atom is radioactive it means it emits (gives out) ionising radiation or particles
- protons and neutrons are held together in the nucleus by strong nuclear forces, this 'binding energy' hold the nucleus together
- when the binding energy is strong enough the nucleus is stable, when it is not the nucleus is unstable
- unstable atoms will lose mass and energy to become stable.
Safety
Irradiation
Irradiation is the forces of exposing an object to ionising radiation. the irradiated object does not become radioactive
Contamination
Contamination is the unwanted presence of materials containing radioactive atoms on other materials.
- the type of radiation emitted affects the level of hazard
Radiation
- nuclear radiation is dangerous due to ionisation out of atoms, making them charged
- when atoms are living cells become ionised one of three things usually happen. - the cell dies, the cell repair itself, or the cell mutates incorrectly and can become cancerous
Activity - Half-life
The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half of its initial level.
The Atom
Diagram
Mass
Isotopes
An element's atomic number defines it. An element with 17 protons will always be chlorine.
However an element's mass numbers can vary, which means that it can have different numbers of neutrons. So although chlorine has a mass number of 35 which means it has 18 neutrons, it can also have a mass number of 37, which means it has 20 neutrons. The different types of chlorine are called isotopes.
Isotopes are forms of an element that have the same number of protons but different numbers of neutrons.
Charge
Ions
Forming Ions
An ion is an atom or group of atoms with a positive or negative charge. Ions form when atoms lose or gain electrons to obtain a full outer shell:
- metal atoms lose electrons to form positively charged ions
- non-metal atoms gain electrons to form negatively charged ions
Forming Positive Ions
Metal atoms lose electrons from their outer shell when they form ions:
- the ions formed are positive, with more protons than electrons
- the ions formed have full outer shells
For elements in groups 1, 2 and 3, the number of electrons lost is the same as the group number.
Forming Negative Ions
The outer shell of non-metal atoms gains electrons when they form ions:
- the ions formed are negative, because they have more electrons than protons
- the ions formed have full outer shells
For groups 6 and 7, the number of electrons gained is equal to (8 - group number).
The numbers of protons, neutrons and electrons in an ion can be calculated from its atomic number, mass number and ionic charge.Remember that:
- atomic number = protons
- mass number = protons + neutrons
- electrons = protons (if atom is neutral)
- positive ions have lost electrons
- negative ions have gained electrons
-