Everything around us is matter, and matter is made up of molecules. Molecules are combinations of atoms of the same element or of different elements. Table, chair, bag, book, chalk and blackboard – everything we see is made up of atoms. This chapter covers the atomic theories of Dalton, Thomson and Rutherford, the sub-atomic particles, atomic number and mass number, isotopes and isobars, and valency.
1. The Atom – How Small Is It?
- Atoms are the smallest particles. They cannot be seen even through a microscope.
- An atom is thousand times smaller than the thickest human hair.
- An atom is the smallest particle of an element that retains its chemical properties.
- Atoms of the same element are identical, and atoms of different elements differ.
Nanometer: a unit used to measure small lengths. One nanometer = 1 × 10^-9 m.