The History of the Modern Periodic Table

History of the Periodic Table Dmitri Mendeleev – first to organize elements according to their properties Mendeleev ordered the elements according to increasing atomic mass Predicted the existence and properties of elements not yet discovered

Henry Mosely British Scientist 1911 Re-ordered the periodic table in order of increasing atomic number instead of mass. Problems with the Mendeleev table disappeared.

History of the Periodic Table Periodic Law: The physical & chemical properties of the elements are periodic functions of their atomic numbers.

History of the Periodic Table Periodic Table: arrangement of elements in order of their atomic numbers so that elements with similar properties fall in the same column.

Periodic Table Geography

Valence Electrons Electrons available to be lost, gained, or shared in the formation of chemical compounds Electrons that are in the outermost electron shell Atoms are most stable when they have 8 valence electrons

The horizontal rows of the periodic table are called PERIODS.

The vertical columns of the periodic table are called GROUPS, or FAMILIES. The elements in any group of the periodic table have similar physical and chemical properties!

Alkali Metals (yellow)

Alkali Metals 1 st column on the periodic table (Group 1) not including hydrogen. Very reactive metals, always combined with something else in nature (like in salt). Soft enough to cut with a butter knife

Alkaline Earth Metals (Blue)

Alkaline Earth Metals Second column on the periodic table. (Group 2) Reactive metals that are always combined with nonmetals in nature. Several of these elements are important mineral nutrients (such as Mg and Ca

Transition Metals (orange)

Transition Metals Elements in groups 3-12 Less reactive harder metals Includes metals used in jewelry and construction. Metals used “as metal.”

Halogens (green)

Halogens Elements in group 17 Very reactive, volatile, diatomic, nonmetals Always found combined with other elements in nature. Used as disinfectants and to strengthen teeth.

Noble Gases (Red)

The Noble Gases Elements in group 18 VERY unreactive, monatomic gases Do not combine with other elements Used in lighted “neon” signs Have a full valence shell.

The Odd Ones

Hydrogen Hydrogen belongs to a family of its own. Hydrogen is a diatomic, reactive gas. Hydrogen is promising as an alternative fuel source for automobiles

Boron Family Elements in group 13 Aluminum metal was once rare and expensive, not a “disposable metal.”

Carbon Family Elements in group 14 Contains elements important to life and computers. Carbon is the basis for an entire branch of chemistry. Silicon and Germanium are important semiconductors.

Nitrogen Family Elements in group 15 Nitrogen makes up over ¾ of the atmosphere. Nitrogen and phosphorus are both important in living things. Most of the world’s nitrogen is not available to living things. The red stuff on the tip of matches is phosphorus.

Metalloids Along the stair step line of the periodic table Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Polonium Have characteristics of both metals and nonmetals

The periodic table is the most important tool in the chemist’s toolbox!

Periodic Trends

Atomic Radii Decrease

Atomic Radii Decrease from left to right because as electrons are added to a sublevel, they are gradually pulled closer to the more highly charged nucleus.

Atomic Radii Increase as you go down each group

Atomic Radii

Ionization Energy Energy required to remove one electron from a neutral atom of an element. Increases left to right across the periodic table. Decreases from top to bottom down a group.

Ionization Energies Increase Ionization Energies Decrease

Electron Affinity energy change that occurs when a neutral atom gains an electron Increases from left to right across each period Decreases from top to bottom down each group Electron Affinity Decreases

Electronegativity measure of an atom’s ability to attract electrons in a chemical compound Increases from left to right across a period Decreases from top to bottom down a group Electronegativity Decreases