John Dalton’s atomic theory (1803) key points
-All matter consists of indivisible atoms
-Atoms of the same element are identical
-Different elements have different types of atoms
John Dalton’s main contributions
He proposed that all matter is made of indivisible atoms and that atoms of the same element are identical
JJ Thomson’s discovery
-Discovered electrons using cathode ray tubes
-proposed the “plum pudding model”
-proved atoms are divisible
In the plum pudding model, atoms are described as:
-Positively charged
-electrons embedded throughout
Earnest Rutherford’s gold foil experiment (1909)
-Shot positive alpha particles at gold foil
Results:
-most particles passed through
-some bounced back (were deflected at large angles, indicating the presence of a dense, positively charged nucleus at the centre of the atom.)
-> this led to the discovery of the nucleus
Rutherford’s nuclear model (1911)
-Features a dense, positive nucleus
-Electrons orbit like planets
Niels Bohr’s model (1913)
-Improved Rutherford’s model
Key concepts:
-electrons in fixed energy levels
-quantum jumps between levels
-energy released as light
James Chadwick’s discovery (1932)
-discovered the neutron
-explained isotopes
-completed basic atomic structure
James Chadwick significance
-explained the “missing mass” in atomic nuclei
-led to more accurate atomic models with protons and neutrons in the nucleus
-enabled better predictions of isotopes and nuclear stability
Relative Atomic Mass
the average of all the different relative isotopic masses of an atom of a particular element
-weighted to account for the relative abundance of each isotope
Relative Isotopic Mass
the mass of an atom of a particular isotope of an element, on the carbon scale
Relative abundance
the proportion of a naturally occurring sample that you would expect to be a that particular isotope
Mass Spectrometry
measures the relative molecular mass of atoms or molecules
-can be used to identify the presence and relative abundance of isotopes in a sample of an element
Mass Spectrometry
1) ionisation
2) acceleration
3) deflection
4) detection
Ionisation
gas particles are bombarded with a stream of high energy electrons (or ultraviolet light), which removes electrons leaving the atom with an overall positive charge
Acceleration and Separation
the positive ions are accelerated by an electric field to produce a high-speed ion beam, which is then directed into a strong magnetic field (this ensures all ions have the same kinetic energy)
Deflection
the individual ions become deflected by the magnetic field and move into circular paths of different radius depending on their mass and charge (mass to charge ration (m/z))
-ions with a lower mass experience more deflection by the magnetic field and so travel a smaller radius
-the greater the charge the greater the deflection
Detection
counts the number of each of the ions m/z ratio
