The Periodic Table

History of the Periodic Table Johann Wolfgang Döbereiner – In 1829 he observed many elements could be grouped into triads (groups of three) based on their chemical properties. Alexandre-Emile Béguyer de Chancourtois – First to arrange the elements in order of atomic weights in 1862 John Newlands – Similar physical and chemical properties recurred at intervals of eight (Law of Ocatves)

History of the Periodic Table **Dmitri Mendeleev – First to be recognized as using the trends in the periodic table to predict the properties of missing elements. Trends were based off of atomic weight due to the fact that the atomic number had not yet been discovered. Lord Rayleigh – Discovered the element argon and the phenomenon of ‘Rayleigh Scattering’ (the reason our sky is blue!!) William Ramsey – Discovered noble gases Henry Moseley – Provided a basis of sorting chemical elements on the periodic table based on their physics.

Properties of the Periodic Table As of June 2011, the current table contains 118 confirmed elements Elements are presented by increasing atomic number (also the number of protons) Broken into periods (horizontal) and groups (vertical) Properties will vary when moving vertically through the groups.

Properties of the Periodic Table Groups: Vertical ‘columns’ Considered the most important method of classifying elements In some groups, elements have very similar properties and exhibit clear trends

Properties of the Periodic Table Periods: Horizontal ‘rows’ Similar properties in the ‘d’-block (transition metals), lanthinide series, and actinide series

Families of the Periodic Table Alkali Metals: Group 1 elements Naturally occurring Highly reactive under standard conditions Alkaline-Earth Metals: Group 2 elements Reactive under standard conditions

Families of the Periodic Table Transition Metals: Groups 3-12 Elements in the ‘d’-block and ‘f’-block All metals Halogens: Group 17 elements Only group that contains all three states of matter

Families of the Periodic Table Inert Gases (Noble Gases): Group 18 elements Colorless, odorless Very low chemical reactivity Outer shell is full of electrons!! Not likely to react….

Periodic Trends Electronegativity: Electron Affinity: Tendency of an atom to attract electrons to itself Electron Affinity: Amount of energy released when an electron is added to a neutral atom and forms a negative ion Ionization Energy: Energy required to remove an electron Atomic Radius: Distance between the nucleus and the edge of the electron cloud

Valence Electrons For main group elements, valence electrons are found in the outermost shell Electrons in the atom that can participate in the formation of chemical bonds