Tuesday, March 3 - Matter - The Periodic Table of Elements

Objective: Understand the Periodic Table of Elements and how elements are classified

As recently as the 1800s, scientists only knew of a few elements. In 1869, the Russian chemist Dmitri Mendeleev compared the various properties of individual elements – color, atomic mass, density, melting point and boiling point. He decided to arrange the elements based on increasing atomic mass (the mass of an atom). In 1913, Henry Moseley, as physicist arranged the elements according to increasing atomic number (the number of protons in an atom) instead of atomic mass. This became the periodic table we know today. Each element on the table has a label that includes the elements name and its properties.

Metals, Nonmetals and Metalloids

Elements are classified into three general categories: metals, nonmetals and metalloids. Metals are exactly what you think – shiny, malleable, conductive elements. Nonmentals are the opposite – dull, brittle and poor conductors. More than half of nonmetals are gases at room tempature. (Think hydrogen.) Mettaloids has some of the properties of metals. They are solid at room temperature and conduct heat and electricity better than nonmetals, but can be shiny or dull, malleable or brittle.

All the elements in a group of the periodic table share certain properties because they have the same number of electrons in the outermost energy level. Groups 1 and 2, along with Groups 13-18 are representative elements – or main group elements. Basically, their behavior is predictable. You know what they’re going to do.  Groups 3-12 are the transition elements – they’re less predictable and could react differently.

Explore the Periodic Table of Elements. Look at the groupings and the labels. Get comfortable with it.