Parts of the Periodic Table Chemistry Parts of the Periodic Table

History of the Periodic Table As scientists discovered new elements and their properties, they began to group elements with similar properties together. By 1868, over 60 elements had been identified. By determining the relative mass of these elements compared to hydrogen scientists could determine the atomic mass (atomic weight) of the element

Dmitri Mendeleev (1834-1907) Made a card for each of the known elements with its properties and atomic mass. When he was finished, he realized the properties of the elements seemed to depend on the atomic mass of the element. By organizing the element cards in rows by increasing atomic mass, Mendeleev could place elements with similar properties in the same column.

Mendeleev’s Periodic Table Based on the theory that element properties periodically repeated as the atomic mass of the elements increased, Mendeleev created a practical periodic table

Mendeleev’s Periodic Table Using this “periodic law”, to arrange all the known elements, Mendeleev’s new table of elements had gaps Mendeleev realized these gaps represented undiscovered elements

Mendeleev’s Periodic Table Despite being able to predict the existence of several undiscovered elements, Mendeleev’s periodic table was not perfect. For a few elements, Mendeleev had to break the rule of increasing atomic mass to place elements in a column with similar properties.

Henry Moseley (1887-1915) Proposed the elements be arranged according to increasing atomic numbers instead of atomic mass. Supported the periodic law introduced by Mendeleev Solved the problems associated with Mendeleev’s periodic table

The Modern Periodic Table Since Moseley, a few changes have been made to make it easier to use and or display The modern periodic table can tell you a lot of information about an element if you know how to “read” it.

Metals, Non-Metals, Metalloids

Metals, Non-Metals, Metalloids Most metals are solid at room temperature, good conductors of heat and electricity, form positive ions, shiny, and are malleable and ductile. Most non-metals are gases at room temperature, poor conductors of heat and electricity (good insulators), form negative ions, and are brittle and dull Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, and Polonium are metalloids. They have some metallic properties and some non-metallic properties.

Groups (Families) Each vertical column (18 total) is given a group / family number. All the elements in a group / family have similar properties (like family members) Some groups / families have special names.

Group 1 – Alkali Metals Include Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium. Very reactive – never found as an element in nature.

Group 2 – Alkali Earth Metals Includes Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium. Slightly less reactive than group 1 metals – Rarely found as an element in nature.

Group 17 - Halogens Includes Fluorine, Chlorine, Bromine, Iodine, and Astatine Reactive non-metals – Rarely found in nature as elements.

Group 18 – Nobel Gases Includes Helium, Neon, Argon, Krypton, Xenon, and Radon Inert non-metal gases – do not form compounds in nature