The Modern Periodic Table

In nature, as well as in things that humankind invents, you may notice some repeating patterns. The seasons repeat their pattern of fall, winter, spring, and summer. The tides repeat their pattern of rising and falling. Tuesday follows Monday,

December follows November, and so on. A pattern of repeating order is called periodicity.  In the mid-1800s, Dmitri Mendeleev, a Russian chemist, noticed a repeating pattern of chemical properties in the elements that order of increasing atomic mass to form something that fairly closely resembles the modern periodic table. He was even able to predict the properties of some of the then-unknown elements.  Later, the elements were rearranged in order of increasing atomic number, the number of protons in the nucleus of the atom. Figure 1.1 shows the modern periodic table.