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- Slide: 1
- john Dalton published his ideas about atoms in 1803. He thought that all matter was made of tiny particles called atoms, which he imagined as tiny spheres that could not be divided.
- discovery of da atom
- alpha particles In 1909 Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, positively charged
- Nearly 100 years later, J J Thomson carried out experiments and discovered the electron.
- This evidence led Rutherford to suggest a new model for the atom, called the nuclear model. In the nuclear model:the mass of an atom is concentrated at its centre, the nucleusthe nucleus is positively charged
- Slide: 2
- Atoms are very, very small. They are too small to be seen, but imaging of atoms by really powerful microscopes is possible. Despite their small size, scientists have managed to find out a great deal about them.atoms have a radius of about 0.1 nm (1 × 10−10 m)the nucleus is less than 1/10 000 of that of the atom (less than 1 × 10−14 m)For comparison, the radius of a typical human hair is about 1 × 10−4 m.If you could count all of atoms in a dot of ink you would find that the number is greater than the population of the world.
- size of da atom
- Slide: 3
- When we write the symbol for an atom, we can place its mass number at the top left and its atomic number at the bottom left.One way to remember the order of these numbers is the word ma: mass number then atomic numberThis is the chemical symbol for sodium• Mass number = 23• Atomic number = 11Number of protons in a sodium nucleus = 11 (the atomic number)Number of electrons orbiting a sodium nucleus = 11. (the atom is neutral)Number of neutrons in a sodium nucleus = 23 – 11 = 12. (mass number - atomic number)
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