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450
Continuum Model
The ancient Greeks believed that all matter was made up of only four fundamental elements:earth, fire, air and water. This was the basis of the continuum model, which predicted that regardless of the number of times you halve a piece of matter, it can always be broken down into even smaller pieces. -
Period: 460 to 370
Solid-ball Model
Greek philosopher Democritus suggested that matter was not continuous but made up of tiny, solid and unbreakable particles. He was the first to use the term 'atomos' meaning "indivisible". -
Plum Pudding Model
British scientist Joseph John Thompson discovered the electron and its negative charge in 1897. However, Thompson knew that there must also be a source of positive charge in the atom to make the atom charge neutral. Therefore, in 1904 he proposed the plum pudding model. In this model, an atom is thought of as a round ball of positive charge with negatively charged electrons embedded in it (like plums or sultanas in a plum pudding). -
Dynamide Model
Hungarian scientist Philipp Lenard described atoms as mostly empty spaces filled with fast-moving 'dynamides'. These were neutrally charged particles made up of a heavy positive particle struck to a light negative particle. -
Neclear Model
New Zealand scientist Ernest Rutherford performed an experimental where he fired a beam of positively charged alpha particles at gold foil. He found that while most alpha particles went through the foil, a small number were deflected. This led to the development of a nuclear model of the atom in which most of the mass believed to be contained in a small positive nucleus surround by a large space occupied by negative electrons. -
Planetary Model
Danish scientist Niels Bohr modified Rutherford's model and proposed that electrons can only travel along certain pathways around the nucleus, called orbits. As a result, this model is sometimes called the planetary model. This model explained why different elements produce different-coloured light when heated. This observation is due to the electrons moving from higher to lower orbits and emitting coloured light in the process. -
Planetary Model With Neutrons
English scientist James Chadwick discovered the neutron, showing that the nucleus was not just a mass of positive charge but a cluster of positively charged protons and charge-neutral neutrons. -
Period: to
Electron Cloud Model
Today, scientists have concluded that the position of an electron in an atom can never be known exactly. This means that it is impossible for electrons to revolve around the nucleus in specific orbits as suggested by Niels Bohr. Instead, the electrons form clouds around the nucleus. Scientists can predict the shape of these clouds but never the exact location of the electrons within them.
