2.2 The Atomic Structure Historical development of atomic models Model Structure CharacteristicDalton’s atomic model The atom wasproposed by John imagined as a smallDalton in 1805 indivisible ball similar to a very tiny ball.Thomson’s atomic J.J Thomson discoveredmodel proposed by J.J. electron, a negatively-Thomson in 1897 charged particle. The atom was described as a sphere of positive charge embedded with electrons.
Model Structure CharacteristicRutherford’s atomic Ernest Rutherfordmodel proposed by discovered proton,Ernest Rutherford a positively-chargedin 1911 particle in an atom. The central region of atom has a very small positively- charged nucleus, which contains almost all the mass of the atom.Bohr’s atomic The electrons in anmodel proposed by atom move in shellsNeils Bohr in 1913 around the nucleus which contains protons.
Model Structure CharacteristicChadwick’s atomic Chadwick provedmodel proposed the existence ofby James Chadwick neutrons, thein 1932 neutral particle in the nucleus. The nucleus of the atom contains protons & neutrons, and the nucleus is surrounded by electrons.
Subatomic particles in atom Proton Neutron Subatomic particles Electron
Properties of subatomic particles Proton, pRelative electric charge: +1Relative mass: 1 Nucleus Neutron, nRelative electric charge: 0Relative mass: 1 Electron, e Relative electric charge: -1 Relative mass: ≈ 0.0005
Proton number and nucleon number Proton number: The number of proton in its atom ** also shows the number of electrons in the atom Nucleon number: The total number of protons and neutrons in its atom ** also known as mass number
What is the relationship??Nucleon Proton Number of = +number number neutrons ORNucleon Number of Number of = +number protons neutrons
Reminder!!! Proton number √ Nucleon number √ Neutron number XNumber of neutron
Symbol of elementsNucleonnumber A Z X Symbol of elementProtonnumber
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