C1.1.3 - Atomic Model

• Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells
• The number of subatomic particles in an atom can be calculated from the atom's atomic number and mass number
• Ideas about atoms have changed over time as scientists developed new atomic models based on experimental evidence
• John Dalton proposed in 1803 that all matter was made of tiny particles called atoms, which he imagined as tiny spheres that could not be divided
• J J Thomson discovered the electron nearly 100 years later and suggested the plum pudding model of the atom, where the atom is a ball of positive charge with negative electrons embedded in it
• Ernest Rutherford's experiment with alpha particles led to the nuclear model of the atom, where the mass is concentrated at the centre in the nucleus, which is positively charged
• In the nuclear model, the nucleus contains protons and neutrons, and has most of the mass of the atom
• Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells
• The number of subatomic particles in an atom can be calculated from the atom's atomic number and mass number
• Niels Bohr adapted Ernest Rutherford's nuclear model and suggested that electrons orbit the nucleus in shells at certain distances
• Protons are subatomic particles with a positive charge and a relative mass of 1, each proton has a small amount of positive charge
• In 1932, James Chadwick found evidence for the existence of neutrons in the nucleus with mass but no charge
• The atomic model was further developed to include neutrons, which is still used today