By 1860, scientists had discovered 60 elements. Elements were divided into groups (similar properties) and periods (regular gradation). This chapter covers the modern periodic table, periodic trends, metallurgy, alloys and corrosion.
1. Modern Periodic Law
- Mendeleev's periodic table had discrepancies. The atomic mass of argon (39.95 amu) is greater than that of potassium (39.10 amu), but argon comes before potassium.
- Argon, an unreactive gas, cannot go in the group of the highly reactive lithium and sodium. The true basis turned out to be the number of protons.
- Henry Moseley, a British scientist, discovered atomic number in 1912. Atomic number = number of protons = number of electrons in the neutral atom.
Modern periodic law: "The physical and chemical properties of the elements are the periodic functions of their atomic numbers."