ATOMIC STRUCTURE AND THE PERIODIC TABLE
Theoretical change with respect to Dalton’s atomic theory
1. In 1803, atomic theory was revived by John Dalton
a) matter is made up of tiny particles called atoms which cannot be created, destroyed or split b) all atoms of one element are identical:- same mass and same chemical properties c) a chemical reaction consists of rearranging atoms from one combination to another. d) When elements combine to form compounds, small whole numbers of atoms form molecules.
However this was proved to be not entirely correct. Atoms have been split as well as created i.e. nuclear reactions. Also there are isotopes, meaning that not all atoms of an element are identical.
Therefore theory was forced to CHANGE in regards to these observations contradicting to the theory put forward by Dalton.
The distribution of charge and mass in an atom
|Particle |Location |Mass |Charge | |Electron |Orbitals |1/1837 unit |-1 unit | |Proton |Nucleus |1 unit |+1 unit | |Neutron |Nucleus |1 unit |0 |
|Term |Definition | |Atomic/proton number |Number of protons in a nucleus of an atom | |Nucleon/mass number |Sum of the number of protons and neutrons in the nucleus of an | | |atom | |Nuclide |Any atomic species of which the proton number and nucleon number | | |are specified e.g. 126C and 94B are nuclides | |Isotopes |Nuclides of the same element or atoms of the same element with | | |different mass numbers | | |NB isotopes have the same chemical properties but different | | |physical properties | |Relative atomic mass |Mass of an atom based on a scale such that the C-12 isotope has a| | |mass of 12.00 units | | |relative atomic mass | | |= mass of 1 atom of an element x 12 | | |mass of 1 atom of carbon-12 |
Phenomenon of radioactivity
Radiation is the spontaneous decay of unstable atoms with the emission of either alpha, beta or gamma radiation.
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (two protons and two neutrons bound together into a particle identical to a helium nucleus) and transforms (or 'decays') into an atom with a mass number 4 less and atomic number 2 less. For example: [pic]
although this is typically written as: [pic]
Beta decay is a type of radioactive decay in which a fast moving electrons is emitted. The new atom has no change in mass number but an atomic number increases by 1. Gamma rays or gamma-ray (denoted as γ) are forms of electromagnetic radiation (EMR) or light emissions of a specific frequency produced from sub-atomic particle interaction, such as electron-positron annihilation and radioactive decay. There is no change in atomic or mass number of the atom.
Band of stability (n/p ratio)
Uses of radioisotopes
1. radiocarbon dating
2. smoke detectors
4. medical uses i.e. tracers or chemotherapy 5. irradiation...
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