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John Dalton - Billiard Ball Model
In 1803, English chemist John Dalton built on Democritus’s idea of invisible particles. He suggested that different substances were made up of different particles that had specific masses and properties, and these are known as elements, using the 'Billiard Ball Model'. From here, Dalton assigned atomic weights to the 20 different elements that were known at the time (Dalton's table of elements, made in 1808), on a sheet of paper that we now know today as the periodic table. -
Joseph John Thomson - Plum Pudding Model
In 1897, physicist Joseph John Thomson discovered a new particle in the atom called the 'electron', which is the first particle in the atom to be discovered. Thomson's 'Plum Pudding Model' (created in 1904) consisted of a positive sphere, and negatively charged electrons spread out throughout the sphere. Thomson also stated that the positive charge of the sphere, and the negative charge of the atoms were of equal magnitude, canceling themselves out, so the atom has a neutralised effect. -
Ernest Rutherford - Nuclear Model
In 1909, Ernest Rutherford performed the Gold Foil Experiment to test if alpha particles would bounce back or scatter after being fired at a piece of gold foil. From Rutherford's observations (done in 1911), most of the particles had passed directly through the foil, and barely any of the particles had scattered or bounced back, and this was caused from a positive charge. These observations led to the Nuclear Model, in which a positively charged nucleus is located in the center of the atom. -
Niels Bohr - Planetary Model
In 1913, Danish physicist Niels Bohr had proposed the planetary model of the atom, in which electrons orbit around Rutherford's previously discovered nucleus, in different shells. Bohr had also proposed that each shell had a maximum number of electrons, before having to use another shell of electrons. Bohr had discovered this with the help of recent experiments, such as Rutherford's 'scattering' experiment, as well as a really complicated 'energy release' experiment of his own. -
Erwin Schrodinger - Quantum Mechanical Model
In 1926, Austrian physicist Erwin Schrodinger used a mathematical equation called 'Schrodinger's Wave Equation' to predict the probable location of an electron. This was made because, theoretically, any scientist can predict, and almost locate where a particle might be using these complicated wave equations. Using the wave equation, Schrodinger created the 'Quantum Mechanical Model', a model similar to a heatmap showing places most likely for an electron to be when measured at any one time. -
James Chadwick - James Chadwick Atomic Model
In 1932, English physicist James Chadwick had discovered the last element of the atom (after electrons and protons), the neutron. Unlike the proton and electron, the neutron doesn't have a charge, and it is a neutral element. Chadwick had discovered the neutron by creating radiation from a radioactive Beryllium isotope, and aimed this at Paraffin wax. Chadwick then measured the range of protons given off, and discovered a particle with the same mass as a proton, but it was 'strangely' uncharged.