L(AtomicStructure).docVIP

1. Introduction to Materials Atoms An atom is the smallest piece of a substance that is still that substance. Virtually everything is made of atoms, but since there are only about 100 different atoms, how come there are millions of different substance in the world? The answer lies in the fact that atoms may form groups, called molecules, or structures called lattices in which they are held together by special forces called atomic bonds. Atomic history/ theory Solids, liquids and gases behave differently owing to the different arrangement of their particles. Ice, water and steam are each made from the same particles, but each have their own properties. Why do the particles behave as they do in each of these three states? What are the particles actually made of? Atomic theory attempts to explain the microscopic structure of materials. According to this theory, all matter is made of atoms. Atoms are so small that it was not until 1981 that their images could finally be seen using the newly invented scanning tunnelling microscope. Ideas about the atom had been refined over many centuries. These new images were very exciting to the scientific community at the time they were developed. 1. About 400 BC Greek philosopher Democritus first suggested that all substances consisted of tiny indivisible particles called atoms.[ atoms, cannot be divided, in Greek] 2. 1808 John Dalton’s atomic theory proposed that: All matter consisted of tiny particles called atoms Atoms could not be divided into smaller particles Atoms of the same element were alike Atoms combined in simple whole number ratios. 3. 1897 English scientist Sir J.J. Thomson’s discovery of the electron showed that atoms were not indivisible. Thomson’s model proposed that atoms were positively charged spheres with negatively charged particles called electrons embedded in them like the fruit in a plum pudding. 4. 1911 Ernest Rutherford proposed a nuc